Optics Seminar

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Previous Lectures

QUEST Center event
Yoad Michael, Bar Ilan
24/05/2017 - 12:00 - 13:00

The Raman spectrum of a sample provides information about the sample's molecular content, with each individual molecule contributing its own typical "fingerprint" spectrum. However, the sensitivity of Raman Scattering as a spectroscopic method is limited by the relatively weak Raman gain of the target molecule. Coherent Anti-Stokes Raman Spectroscopy (CARS) was developed to increase the measured Raman signal by exciting the sample with two light sources: the pump and an idler with a frequency difference from the pump that matches a vibrational energy gap of the molecule being probed. However, this method introduced noise due to the non-resonant background from surrounding materials (e.g solvents) which obscures the spectrum of the target Raman molecule. Several methods used for reducing the non-resonant background, such as epi-CARS, polarization-CARS and pulse shaping techniques can surpass the non-resonant signal to some extent, but not completely reduce to the shot-noise level, resulting in low sensitivity for possible spectroscopic and imaging applications. 

The nonlinear interaction in CARS is Four-wave mixing (FWM), which converts two pump photons into signal and idler photons that obey specific relative phase relations, and experience two-mode quadrature squeezing, as previously researched in our group. We approach the problem by performing a doubly-stimulated CARS process, allowing us to exploit the unique correlation properties of the FWM light for measuring the phase shift introduced by the non-resonant FWM process, and effectively converting the standard intensity measurement into an interferometric phase measurement.  Our proposed method completely rejects the non-resonant background below the shot-noise limit and enhances the effective Raman signal. 

Prof. Adrian Stern, Ben Gurion University
17/05/2017 - 12:00 - 13:00

The theory of Compressive Sensing, a.k.a. Compressed Sampling (CS), was introduced a little more than a decade ago and it has generated a great deal of attention in a variety of areas, including applied mathematics, computer science, physics,  engineering and, in fact, almost every field that involves data sensing. The  CS theory offers a much more economical sensing framework, in terms of number of samples, compared to the traditional Shannon-Nyquist paradigm. The CS theory has found natural application for optical sensing and imaging due the large dimensionality of optical data.  By employing CS principles for optical imaging and sensing it is possible to reduce the overall acquisition time, the amount of data stored and transmitted, and the size and weight of the system. In this talk we overview the opportunities opened by compressive sensing to overcome optical sensing and imaging design limitations. Examples form our decade activity in the field will be given, including compressive 2D and 3D imaging, 4D spectral-volumetric imaging, hyperspectral and ultraspectral imaging, motion tracking and more.

 

 

Adrian Stern-short biography

 

Adrian Stern received his B.Sc., M. Sc. (cum laude) and PhD degrees from Ben-Gurion University of the Negev, Israel, in 1988,1997 and 2003 respectively, all in  Electrical and Computer Engineering. Currently he is a Full Professor at Electro-Optical Engineering Department at Ben-Gurion University in Israel where he serves as department head. During the years 2002-2004 he was a postdoc fellow at University of Connecticut. During 2007-2008 he served as senior research and algorithm specialist for GE Molecular Imaging, Israel. In 2014-2015, during his sabbatical leave, he was a visitor scholar and professor at Massachusetts Institute of Technology (MIT).

His current research interests include compressive imaging and optical sensing, 3D imaging, computational imaging, remote sensing,  phase-space optics.  

Dr. Stern has published almost 160 technical articles in leading peer reviewed journals and conference proceeding, more than quarter of them being invited papers.

Dr. Stern is a Fellow of SPIE, member of IEEE, OSA. He served an associate editor for Optics Express journal for six years, and served as guest Editor for IEEE/OSA Journal on Display Technology. He has edited the first book on Optical Compressive Sensing and Imaging published by CRC Press in 2016.

 

QUEST Center event
Prof. Ömer Ilday, Bilkent University, Turkey
10/05/2017 - 12:00 - 13:00

Looking at how structure and functionality arise in Nature, the role of emergent phenomena is evident and ubiquitous, from pattern formation in a sand pile, all the way up, in complexity, to the primate brain. In contrast, we rarely see deliberate use of these principles in human-made systems. Could we incorporate the same principles of operation and adaptability of, say, a bacterium, in a way that complements traditional engineering? 

We propose that superior technological functionalities that are difficult or impossible to achieve with linear and near-thermal-equilibrium systems can be obtained by exploiting nonlinear dynamics far from equilibrium. I will begin by briefly describing our main experimental tool, the mode-locked laser, which generates intensely powerful pulses that we use to deliver the energy that drives our systems far from equilibrium. It is telling that mode-locking, itself a self-organized, emergent phenomenon with great technological applications, has provided much of our early guidance about controlling such systems. I will then exemplify how we orchestrate the complex dynamics of physically very different systems, whereby we exert control over spatial scales that vary from the sub-micron to the atomic and vastly improve or introduce unprecedented new capabilities, addressing long-standing engineering problems in each case. 

QUEST Center event
Hanan Herzig Sheinfux (Moti Segev's group), Technion
03/05/2017 - 12:00 - 13:00

Anderson localization is a cornerstone of our understanding of the interaction of light with disorder. But in the deep subwavelength regime, all photonic transport effects, including Anderson localization, become trivialized and effective medium theory should take over.

This talk will present work on subwavelength disordered multilayer structures – stacks of dielectric layers, where each is layer has an average thickness of lambda/40 (experimentally) or lambda/1000 (theoretically). But rather than being a weak effect, localization in this regime dominates transport completely and induces a rich regime of transport where disorder can sometimes increase transmission rather than reduce it. Furthermore, changing a single layer by 2 nm is shown to have a measurable effect on transport in visible wavelengths.

Prof. Dr. Xing ZHU, School of Physics, Peking University and National Center for Nanoscience and Technology
26/04/2017 - 12:00 - 13:00

(I) Surface plasmon polaritons (SPPs) have shorter wavelengths and stronger field enhancement, confined to the dielectric-metal interface, in comparison with light and have been widely used in nano-optics, resonance sensing and imaging, including surface plasmon focusing. However, the low conversion efficiency and high propagation loss of SPPs limit its use. Controlling the propagation direction of SPPs by using nanostructures on metal surfaces is important. The manipulating of the focusing and polarization in plasmonic nanostructures is the key problems. In this lecture, we will introduce the principle and experimental of Near-field Optics, and then report the recent progress in the following aspects at Plasmonic-SNOM group, Peking University:

* Surface Plasmons in Metal

Magnetic Fano Resonance; Toroidal Dipolar Resonance; Active Control of Graphene-Based Unidirectional Surface Plasmon Launcher

* Surface Plasmons in 2D materials

Plasmonic hot electron induced structural phase transition in MoS2 monolayer; Graphene quantum dots doping of monolayer MoS2; Active Plasmonic Tuning of MoS2 Absorption and Luminescence

* Plasmonic circular polarization and Focusing surface plasmon polaritons in Archimedes’ nanostructure

(II) Nanotechnology becomes a worldwide important area. To face the challenge, China has established several key institutions around the country. One of the most important one is the National Center for Nanoscience and Technology, which is a highly interdisciplinary research institute, with the initial members of Peking University, Tsinghua University and Chinese Academy of Sciences. After 10 years of construction and running, the Center becomes the best nanotechnology research center of the country, with young scientists of physics, chemistry, biology, information, material science and medical-pharmaceuticals. We will show you the recent activities of this dynamic center.

About the Speaker:

Prof. Xing ZHU (朱星) is the leader of the Plasmonics-SNOM group of School of Physics, Peking University. He obtained Ph.D. of Natural Science at University of Saarland, Germany in 1986 and M.Sc. at University of Toronto, Canada in 1983. He has been working with scanning probe microscopy with special interests in near-field optical microscopy, the structure analysis of nanomaterials, basic theory of surface plasmon polariton and the application of Plasmonics. He was the Chair of 2nd APNFO (1999), the Chair of 10th NFO-international conference for Near-field Optics (2010). He is the council member of Chinese Physical Society, the council member of Association for Asia-Pacific Physical Societies, Member of IUPAP, Commission C2 and Expert of ISO TC229 Nanotechnologies.

Prof. Zhu is also The Deputy Direction of National Center for Nanoscience and Technology, representing Peking University.

QUEST Center event
Mikhail N. Kiselev, International Center for Theoretical Physics, Trieste, Italy
19/04/2017 - 12:00 - 13:00

 

We propose a universal approach to Landau-Zener (LZ) problem in a multilevel system. The problem is formulated in terms of generators of
SU(N) algebra and maps the Hamiltonian onto the effective anisotropic pseudospin (N-1)/2 model. The vector Bloch equation for the density matrix describing the temporal evolution of the multilevel crossing problem is derived and solved analytically for two generic cases: i) three-level crossing problem representing a minimal model for a LZ interferometer and ii) four-level crossing problem corresponding to a minimal model of coupled interferometers. It is shown that the analytic solution of the Bloch equation is in excellent quantitative agreement with the numerical solution of the Schroedinger equation for the 3- and 4- level crossing problems. The solution demonstrates oscillation patterns which radically differ from the standard patterns for the two-level Landau- Zener problem: "beats",  when the dwell time in the interferometer is smaller compared to a  tunnel time and "steps" in the opposite limit. The possibilities of the experimental realization of LZ interferometers in the system of in two-well traps in optical lattices for ultra-cold gases are discussed. 
QUEST Center event
Prof. Carmel Rotschild, Technion
29/03/2017 - 12:00 - 13:00

Nimrod Kruger­, Matej Kurtulik, Assaf Manor, Tamilarasan Sabapathy and Carmel Rotschild

Department of Mechanical Engineering, Technion − Israel Institute of Technology, Haifa 32000, Israel

The radiance of thermal emission, as described by Planck’s law, depends only on the emissivity and temperature of a body, and increases monotonically with temperature rise at any emitted wavelength. Nonthermal radiation, such as photoluminescence (PL), is a fundamental light–matter interaction that conventionally involves the absorption of an energetic photon, thermalization, and the emission of a red-shifted photon. In this quantum process, radiation is governed by the photon rate conservation and thermodynamically described by the chemical potential. Until recently, the role of rate conservation when thermal excitation is significant had not been studied in any nonthermal radiation, leaving open many questions; for example, what is the overall emission rate if a high quantum efficiency PL material is heated to a temperature where it thermally emits a rate of 50photons/sec at its bend edge, while in parallel, the PL is excited at a rate of 100photons/sec? Here we experimentally demonstrate that the answer is an overall rate of 100 blue-shifted photons/sec. In contrast to thermal emission, the PL rate is conserved if the temperature increases, while each photon is blue-shifted. A further rise in temperature leads to an abrupt transition to thermal emission where the photon rate increases sharply[1]. We also demonstrated how endothermic-PL generates orders of magnitude more energetic photons than thermal emission at similar temperatures. These findings show that PL is an ideal optical heat pump, and can harvest thermal losses in photovoltaics with theoretical maximal efficiency of 70%. Solutions of the rate equations for non-ideal quantum efficiency, experimentally measured absorption spectrum and available cavities for photon recycling predict a practical device that aims to reach 48% efficiency[2].

 


[1] A. Manor, L. L. Martin and C. Rotschild, Conservation of photon rate in endothermic-photoluminescence and its transition to thermal emission. OPTICA, Vol. 2, 6, 585  (2015). (IF-5.2, 4 citations)

[2] A. Manor, N. Kruger, T. Sabaphati and C. Rotschild, Thermally-Enhanced Photoluminescence for Heat Harvesting in Photovoltaics, Nat. Commun. DOI:10.1038/ncomms13167 (2016). Also Optics & Photonics news December (2016)

QUEST Center event
Prof. Baruch Fischer, Technion
15/03/2017 - 12:00 - 13:00

I will first briefly describe our work on Many-Body Photonics, that shows the role of noise and entropy in optics and lasers. An important example of this study reveals that mode-locking, which is one of the most important laser effects, is nothing but a first order phase transition. I then discuss several classical condensation phenomena in lasers, and finally describe recent experimental and theoretical results on  photon gas thermalization and lasing without an overall inversion that are unusual in lasers, and reach the possibility to observe quantum photon Bose-Einstein condensation (BEC) in standard fiber cavities at a room temperature. All these effects are done with regular erbium-doped fibers.

Gadi Eisenstein, Electrical Engineering Department and Russel Berrie Nanotechnology Institute
22/02/2017 - 12:00 - 13:00

InAs/InP base quantum dots constitute the gain medium of the most advanced semiconductor lasers and amplifiers. Their superb properties stem from fundamental reasons and major advances in material growth and nano fabrication.

This talk highlights the dynamical properties of these lasers which have three important time scales:

  • Several ps which determines the temperature insensitive modulation characteristics where record speeds have been demonstrated.
  • 1-2 ps which determines the carrier relaxation dynamics into the quantum dots and the gain nonlinearities.
  • Sub 2 fs which is shorter than the coherence time at room temperature and allows for quantum coherent interactions using practical optical amplifiers.

A series of experiments and various models for each of the time scales will be presented and the impact of further developments in quantum dot technologies will be discussed.

QUEST Center event
Prof. Nir Davidson, Weizmann Institute of Science
15/02/2017 - 11:45 - 13:00

I will present the effect of thermal atomic motion on slow light using electromagnetically induced transparency (EIT). A direct consequence of the diffusion of atoms is the coherent diffusion of a stored image throughout the storage duration. The complex amplitude undergoes diffusion and therefore interference occurs. Specifically, high-order Gaussian transverse-modes are topologically stable and self-similar upon storage. During the slow propagation of the probe in the medium, the combined light-matter excitation exhibits both diffraction and diffusion-like behavior

 

Alexander Kaiser, University of Innsbruck, Austria
01/02/2017 - 14:00

Optical absorption of individual molecular ions and clusters can be measured by tagging with helium or other rare gas atoms. In case a resonance is hit by the laser frequency, the molecular ion is electronically excited, and the large amount of internal energy leads to boiling off helium. The signal that can be measured is the ratio in intensity between mass spectra with and without illumination, and extrapolation can be used to accurately approximate the gas phase spectrum. These experiments require the preparation of van-der-Waals bound complexes at very low temperatures. C60+ could finally and unambiguously be confirmed as a carrier of diffuse interstellar bands by the Maier group using a trap with helium buffer gas cooling [1]. Alternatively, the cold complexes can also be produced in helium nano-droplets, where an atomically resolved phase transition could be measured in the Scheier group [2]. A record shall be given from the viewpoint of an interested observer of these experiments and of theoretical approaches and ongoing calculations for such systems. 

 

[1] Campbell, E. K., Holz, M., Gerlich, D. & Maier, J. P. Laboratory confirmation of C60+ as the carrier of two diffuse interstellar bands. Nature 523, 322-323, doi:10.1038/nature14566 (2015).

[2] M. Kuhn, M. Renzler, J. Postler, S. Ralser, S. Spieler, M. Simpson, H. Linnartz, A. G. G. M. Tielens, J. Cami, A. Mauracher, Y. Wang, M. Alcamí, F. Martín, M. K. Beyer, R. Wester, A. Lindinger, P. Scheier, Nature Communication, 2016, DOI: 10.1038/ncomms13550

QUEST Center event
Prof. Ron Folman, Ben Gurion University
18/01/2017 - 12:00 - 13:00


Matter-wave interferometry provides an excellent tool to investigate the effect of the environment on coherence. I will present several interferometry experiments done with a BEC on an atom chip and in which different effects of the environment have been investigated. First, I will discuss effects of fluctuations in the nearby environment probed with atoms trapped in a lattice very close to the surface. Then I will present the effect of gravity probed by clock interferometry, which connects to the interplay of QM and GR and “clock complementarity”. Finally, I will discuss Stern-Gerlach interferometry and describe it in the context of time irreversibility.
 

Dr. Kobi Lasri, VGEN - Spectra-Physics
11/01/2017 - 12:00 - 13:00

Pulsed fiber lasers have created new opportunities in commercial micromachining applications requiring superior processing speeds for small, precise features. Specifically, the growing demand for mobile device manufacturing and renewable energy related applications have paved the way for IR and Green fiber based lasers to become a key enabling technology, harnessing their typical characteristics such as high flexibility and efficiency combined with low maintenance and cost. In this talk we review the recent advances in Spectra-Physics’ V-Gen pulsed fiber laser technology offering state-of-the-art pulse energies, peak powers, and flexibility for modern micromachining applications, including touch panel displays, Li-ion battery, solar cell, semiconductor, and PCB processing.

 

Avi Zadok, Bar Ilan University
04/01/2017 - 12:00 - 13:00

Optical fibers support guided acoustic modes. These modes are stimulated by optical waves, and induce scattering and modulation of light. These interactions are referred to as guided acoustic waves Brillouin scattering (GAWBS) [1]. Here we describe a new application of GAWBS in fiber sensing, and extend the study of the effect to multi-core fibers (MCFs).

Optical sensors typically rely on absorption, index or scattering. These require spatial overlap between light and the test substance. Standard fibers do not provide such overlap. Hence, chemical sensors rely on photonic crystal fibers, or structural modifications. The transverse profiles of acoustic modes reach the outer cladding boundary. Acoustic oscillations are therefore affected by dissipation to the surrounding medium. We employ GAWBS in sensing of liquids outside unmodified, standard fibers [2]. Acoustic waves are stimulated and monitored from within the core. The mechanical impedance of water and ethanol is measured with 1% accuracy. The method can distinguish between aqueous solutions of different salinity [2].

MCFs are often designed to exhibit weak coupling among cores. Nevertheless, we show that acoustic modes lead to opto-mechanical inter-core cross-talk in MCFs. Analytic expressions are derived for the magnitude and spectrum of inter-core, cross-phase modulation (XPM) that is induced by GAWBS. The spectrum consists of a series of narrowband resonances. The effect is experimentally observed in a commercially-available, seven-core fiber. Agreement between analysis and measurement is excellent. On resonance, the magnitude of opto-mechanical XPM is comparable with the intra-core Kerr effect.

Last, we employ GAWBS in a new electro-opto-mechanical radio-frequency oscillator. An optical pump stimulates guided acoustic modes, which modulate the phase of a co-propagating optical probe. The probe modulation is detected and fed back to drive the pump modulation. With sufficient feedback, stable, single-mode oscillations at acoustic resonance frequencies are achieved. No electrical filtering is required.

References

[1] R. M. Shelby, M. D. Levenson, and P. W. Bayer, "Guided acoustic-wave Brillouin scattering," Phys. Rev. B 31, 5244-5252 (1985).

[2] Y. Antman, A. Clain, Y. London and A. Zadok, "Optomechanical sensing of liquids outside standard fibers using forward stimulated Brillouin scattering," Optica 3, 510-516 (2016).

QUEST Center event
Ronen Shriki, Weizmann Institute
28/12/2016 - 12:00 - 13:00

In recent years there have been extensive efforts to solve hard computational problems by realizing physical systems that can simulate specific problems. Here we present a new method in which a modified degenerate cavity (MDC) is used to solve hard computational tasks. The MDC possesses a huge number of degrees of freedom (300,000 modes in our system) that can be coupled and controlled. Specifically, the MDC allows direct access to both the x-space and k-space components of the lasing mode. Placing constraints on these components can be mapped to different computational minimization problems. Due to mode competition, the laser selects the mode with minimal loss and finds an optimal solution.  Details of our experimental system will be presented, as well as recent results demonstrating the ability to use the MDC for simulating XY spin systems and finding their ground state, for phase retrieval, for imaging through scattering medium and more. 

QUEST Center event
Prof. Robert E. Continetti, Department of Chemistry and Biochemistry, University of California, San Diego
14/12/2016 - 12:00 - 13:00

Linear electrostatic traps are a powerful experimental tool with applications ranging from experimental studies of the molecular reaction dynamics of four-atom systems using photoelectron-photofragment coincidence (PPC) studies to massive (micron-sized) particles. Examples of applications to molecular reaction dynamics will be provided by our recent study of the dissociative photodetachment of the F¯(H2O) anion. In concert with state-of-the-art theory, these benchmark studies are providing a foundation for a first-principles understanding of ever-more complex chemical phenomena. To illustrate applications to nanoparticles, a new nanoparticle accelerator/decelerator capable of preparing single mass- and charge-selected nanoparticles for impact studies on surfaces will be discussed.

This work was supported by the U.S. Department of Energy Office of Science, Office of Basic Energy Sciences under Award Number DE-FG03-98ER14879 and the NSF Division of Chemistry under grant CHE-1229690.

QUEST Center event
Eliahu Cohen, University of Bristol
30/11/2016 - 12:00 - 13:00

Quantum mechanics exhibits several peculiar properties, differentiating it from classical mechanics. One of the most intriguing is that variables might not have definite values. A complete quantum description provides only probabilities for obtaining various eigenvalues of a quantum variable. The eigenvalues and corresponding probabilities specify the expectation value of a physical observable, but they are known to be statistical properties of large ensembles. In contrast to this paradigm, we demonstrate a unique method allowing to measure the expectation value of a physical variable on a single particle, namely, the polarization of a single protected photon. This is the first realization of quantum protective measurements [1,2], which are based on a combination of weak measurements and the quantum Zeno effect. Before discussing these issues, I will review the notion of weak measurements [3-5] and discuss their realization by presenting our previous experiment [6], where we measured two non-commuting observables, on one and the same photon, using sequential weak measurements. I will conclude by discussing a few applications of these methods, both in metrology and in the study of foundational questions.

References
[1] Y. Aharonov, L. Vaidman, Measurement of the Schrӧdinger wave of a single particle, Phys. Lett. A 178, 38 (1993).
[2] Y. Aharonov, E. Cohen, Protective measurement, Post-selection and the Heisenberg representation, in Protective measurement and quantum reality: Towards a new understanding of quantum mechanics, Shan Gao (Ed.), Cambridge University Press (2014), arXiv: 1403.1084.
[3] Y. Aharonov, D.Z. Albert, L. Vaidman, How the result of a measurement of a component of the spin of a spin-1/2 particle can turn out to be 100, Phys. Rev. Lett. 60, 1351 (1988).
[4] Y. Aharonov, E. Cohen, A.C. Elitzur, Foundations and applications of weak quantum measurements, Phys. Rev. A 89, 052105 (2014).
[5] Y. Aharonov, E. Cohen, A.C. Elitzur, Can a future choice affect a past measurement's outcome?, Ann. Phys. 355, 258-268 (2015).
[6] F. Piacentini M.P. Levi, A. Avella, E. Cohen, R. Lussana, F. Villa, A. Tosi, F. Zappa, M. Gramegna, G. Brida, I.P. Degiovanni, M. Genovese, Measuring incompatible observables of a single photon, Phys. Rev. Lett.. 117, 170402 (2016).

David Petiteau, Bar Ilan University
23/11/2016 - 12:00 - 13:00

The metamaterials community has been heavily excited since the publication of two articles by Pendry and Leonhardt in 2006, in which exotic devices, such as invisibility cloaks were proposed to be implemented by space transformation. Indeed, the form invariance of the Maxwell equations allow for an equivalence between a deformed geometry and a material with specific properties. Since then, several experimental studies have shown the feasibility of such transformed devices. The form invariance was also found in other physical domains and the space transformations were applied to many physcial phenomena such acoustic wave propagation, elasto-dynamic wave and surface wave propagation. We present in this work the space transformation applied to the heat equation. Throughout our study, we focus on the transformations leading to thermal invisibility cloaks and thermal concentrators. Those transformed devices are made of anisotropic heterogeneous materials which make them difficult to practically design. Therefore, we make use of the two-scale homogenization theory , allowing to approach the behavior of those devices with an alternate set of isotropic materials. We systematically try to evaluate quantitatively the performance of our approximate devices by defining an effectiveness criterion to achieve high level of mthermal metamaterials engineering. Finally, we present a model of a 50-layer carpet cloak, whose first results are to be expected.

QUEST Center event
Barak Dayan, Weizmann Institute of Science
16/11/2016 - 12:00 - 13:00

The most convenient way to send a quantum state from one quantum system to another, remote, one is by using single photons.

So far there have been very few demonstrations of such 'photonic quantum links', and those can be categorized into three types, one of them demonstrated in our group. I will review these three approaches and present the corresponding experimental demonstrations, from other labs worldwide, and from ours.

QUEST Center event
Avi Pe'er, BIU
09/11/2016 - 12:00 - 13:00

 

The discovery of gravitational waves in LIGO (Light Interferometer Gravitational-waves Observatory) was ground-breaking. Suddenly, experimental astro-physics has not just eyes, but also ears to listen to events that shake the sky, yet occur in complete electromagnetic darkness, such as collisions of black-holes. I will overview the recent observation of a violent black-hole collision 1.3 billion light-years away, and provide an overview of this truly amazing device that relies on optical interferometry to detect miniscule ripples in space-time with relative sensitivity of 10-22 ! I will discuss the plans to enhance the LIGO sensitivity even further using quantum squeezed light.
Prof. Ofer Levi, Toronto
01/11/2016 - 12:00 - 13:00

Advances in medicine and technology are opening a new era of portable healthcare. Together with health apps, wearable/portable health monitoring systems are targeting medical diagnosis or health and wellness. The development of Wearable Health Monitoring Systems (WHMS) has been motivated mainly by increasing healthcare costs and by an aging world population. Optical techniques are widely used in clinical settings and in biomedical research to interrogate bio-molecular interactions and to evaluate tissue dynamics. Miniature integrated optical systems for sensing and imaging can be portable, enabling long-term imaging studies in living tissues.  Fluorescent dyes are frequently used to mark biological samples, and track tissues, cells and individual molecules. In the lab, fluorescence is used to understand physiology and develop new cures to common diseases. In the clinic, fluorescence is used to diagnose health conditions and to evaluate treatments. Translating fluorescence imaging to portable healthcare systems will help us take better care of ourselves.

This seminar will review fundamental properties of fluorescence, tissue absorption and scattering and show how these can be used to track vital signs and provide wellness indicators during a physical activity. We will review examples of portable imaging systems in rapid disease diagnosis, and in health monitoring.

Biography

Dr. Ofer Levi is an Associate Professor in the Institute of Biomaterials and Biomedical Engineering and the Edward S. Rogers Sr. Department of Electrical and Computer Engineering at the University of Toronto, currently on a Sabbatical leave at Stanford University. Dr. Levi received his Ph.D. in Physics from the Hebrew University of Jerusalem, Israel in 2000, and worked in 2000-2007 as a Postdoctoral Fellow and as a Research Associate at the Departments of Applied Physics and Electrical Engineering, Stanford University, CA.  He serves as an Associate Editor in Biomedical Optics Express (OSA) and is a member of OSA, IEEE-Photonics, and SPIE.  His recent research areas include biomedical imaging systems and optical bio-sensors based on semiconductor devices and nano-structures, and their application to bio-medical diagnostics, in vivo imaging, and study of bio-molecular interactions.  More details can be found at http://biophotonics.utoronto.ca/

Prof. Lev Deych, Queens College of CUNY, New York
05/10/2016 - 12:00 - 13:00

During the last decade significant experimental efforts were devoted to developing detectors of nanosized -objects using whispering-gallery-mode resonances. The ultimate goal of these efforts is to achieve detection and determination of the size of a single protein. In this talk I will present recent developments concerning theoretical description of particle-induced modifications of whispering-gallery-modes both in strong and weak coupling regimes. Comparison of the theory with experimental data and ways to improve sensitivity of detection will be discussed.

Natan T. Shaked, Department of Biomedical Engineering, Tel Aviv University
15/06/2016 - 12:00

We present multimodal wide-field optical interferometric microscopy techniques for label-free 3-D imaging of live cells during fast flow. Using cell micro-manipulation approaches, multiple cells are trapped and rapidity rotated, while acquired using optical interferometry. The interferometric projections are rapidly processed into the 3-D refractive-index profile of the cells. The potential of these new techniques is for label-free image analysis and sorting of cells, to substitute current cell sorting devices which are based on external labeling that eventually damages the cell sample. We show possible applications to in-vitro fertilization and cancer diagnosis.
 
Prof. Natan T. Shaked is an Associate Professor in the Department of Biomedical Engineering at Tel Aviv University, Israel. Between April 2011-July 2015, he was a Senior Lecturer (Assistant Professor) in the same department. Previously, Prof. Shaked was a Visiting Assistant Professor in the Department of Biomedical Engineering at Duke University, Durham, North Carolina, USA. Prof. Shaked heads the The Biomedical Optical Microscopy, Nanoscopy and Interferometry Research Group, a large experimental group performing a multidisciplinary research involving optical engineering, imaging and sensing in biological systems, optical therapy, and biophysics. Prof. Shaked raised more than 4 Million USD for research, including recent winning in the personal ERC grant (>1.9 Million Euro). He is the author of more than 50 refereed journal papers and more than 80 conference papers.

Avraham Klein, Hebrew Univeristy
01/06/2016 - 12:00

Many quantum systems share interesting features with wave propagation in disordered media, such as apparently diffusive dynamics with an underlying coherent structure. The interplay of these properties is interesting both from a fundamental standpoint and for applications.  

I will discuss one such problem: the statistical properties of an N-photon packet in a random elastically scattering medium. I will describe how information about the quantum state of the packet is encoded in the photon speckle pattern, how it can be measured, and why such measurements become exponentially sensitive with N. Finally I will discuss how state information is hidden in long-ranged correlations of the photon speckles.

Patrice Bertet, Quantronics Group, SPEC, CEA, CNRS, Université Paris-Saclay
25/05/2016 - 12:00

The detection and characterization of paramagnetic species by electron-spin resonance (ESR) spectroscopy has numerous applications in chemistry, biology, and materials science [1]. Most ESR spectrometers rely on the inductive detection of the small microwave signals emitted by the spins during their Larmor precession into a microwave resonator in which they are embedded. Using the tools offered by circuit Quantum Electrodynamics (QED), namely high quality factor superconducting micro-resonators and Josephson parametric amplifiers that operate at the quantum limit when cooled at 20mK [2], we report an increase of the sensitivity of inductively detected ESR by 4 orders of magnitude over the state-of-the-art, enabling the detection of 1700 Bismuth donor spins in silicon with a signal-to-noise ratio of 1 in a single echo [3]. We also demonstrate that the energy relaxation time of the spins is limited by spontaneous emission of microwave photons into the measurement line via the resonator [4], which opens the way to on-demand spin initialization via the Purcell effect. Finally we report recent results demonstrating that squeezed microwave signals can be used to enhance ESR sensitivity even further [5]

[1] A. Schweiger and G. Jeschke, Principles of Pulse Electron Magnetic Resonance (Oxford University Press, 2001)

[2] X. Zhou et al., Physical Review B 89, 214517 (2014).

[3] A. Bienfait et al., Nature Nanotechnology 11, 253 (2016)
[4] A. Bienfait et al., Nature 531, 74 (2016)
[5] A. Bienfait et al., in preparation (2016)

Denis Borodin
04/05/2016 - 12:00

The effect of Parametric Down Conversion (PDC) has been used widely as a source of non-classical states of electromagnetic radiation, such as entangled photons, squeezed light, single photons. The extension of quantum optics into the x-ray regime would open new possibilities for research. Despite the fact, that PDC in X-ray regime has been proposed about 45 years ago, no evidence of non-classical states of light in this regime has been reported yet. The main challenge is Compton scattering. Typically it is many orders of magnitude larger than PDC and completely outweighs the signal from PDC. Perhaps, even more serious problem is that Compton scattering limits the input flux to a level at which Compton scattering starts saturating the detectors.

I will describe an experiment demonstrating the possibility to generate collinear x-ray photon pairs with highly suppressed background. By choosing angles near 90 degrees between the detectors and the pump beam, where the pump polarization is in the scattering plane, we improve the signal-to-noise ratio by nearly three orders of magnitude. We measure about two coincidence counts per second with a bandwidth of 1.5 keV at the full width at half maximum.

Andre Stefanov
13/04/2016 - 12:00

Broadband energy-time entangled photon pairs are produced by pumping a non-linear crystal with a cw laser. Because of their quantum nature, they exhibit at the same time narrowband and short time features. Indeed the sum energy of both photons is equal to the well defined energy of the pump photon, whereas the correlation time between the two photons is of the order of few tens of femtoseconds. Those properties can be used for measurements beyond the capabilities of classical devices.
 
Here we make use of those features to study the temporal properties of photons through various media. The propagation of the entangled two-photon quantum states is described by a temporal wavefunction which is comparable for certain aspects to the one of coherent ultrashort laser pulses. However, because this light is in a continuous way regime, femtosecond timing can be performed without relying on ultrashort laser pulses of high intensities. As application, we show a proof of principle experiment where ultrafast optical coincidences of the photon pairs allow selecting only the ballistic photons for imaging through a scattering medium. Using techniques from the ultrafast optics, we are able to manipulate the two-photon wave function with the help of a pulse shaper and reconstruct the dispersion properties of a sample. Ultimately the precise temporal control of the two photon wavefunction can lead to the implementation of proposals for two-photon spectroscopy with entangled photons, allowing to reveal new properties of the investigated molecules.
 
Finally we present how the same shaping method of the wavefunction allows to encode high dimensional quantum information in the spectrum of the photons and to realize quantum information protocols.

Yossi Mandel, Faculty of Life Science, Optometry Track and Bar-Ilan's Institute for Nanotechnology and Advanced Materials (BINA), Bar-Ilan University
30/03/2016 - 12:00

In outer retinal degeneration, such as Retinitis Pigmentosa or Age related Macular Degeneration, the retinal photoreceptors degenerate while the inner retinal neurons are relatively preserved. Stimulation of these neurons by various technologies was shown to elicit visual percepts. Nevertheless, the visual acuity obtained by current retinal prosthesis is still very poor, probably due to a combination of technical and neural effects. An alternative emerging technology is the transplantation of photoreceptors differentiated from stem cells. Although this is a promising approach, the complexity of the photoreceptor differentiation process, pathology of the host retinal pigment epithelium and inadequate integration of the photoreceptors into the host retina, make this approach very challenging. In this lecture I will present our experience with both photovoltaic retinal prosthesis and with generation of photoreceptors from human embryonic stem cells, as potential technologies for restoration of sight. I will also introduce our novel head mounted DMD based projection system for natural and prosthetic visual stimulation in behaving animals.

Yaakov Shaked
16/03/2016 - 12:00

Squeezed states of light are a major quantum resource in quantum optics. Their unique non-classical correlations (photon-number correlation and phase anti-correlation beyond the shot-noise limit) are a key to many quantum information applications, such as continuous variable quantum computing, quantum communication and key-distribution, teleportation, and sub-shot-noise interferometry.
Quadrature squeezing or squeezed light can span a full bandwidth of pair frequency modes that contribute together to the collective quadratures of the squeezed oscillation. The frequency separation between the modes of a pair can be anywhere between zero (degenerate squeezing) to an optical octave, and the number of simultaneous pairs is generally unlimited (an octave-spanning spectrum was demonstrated). In most experiments however, only the very special case of (nearly) degenerate squeezing is used, or just a single pair. While broad bandwidth is a welcomed resource in many other fields, the use of squeezed states is limited to narrow, almost DC, bandwidth. This is primarily due to the inherently limited bandwidth of optical homodyne measurement, which is the major tool to measure and manipulate squeezed states, and to the incompatibility of standard mode locking methods to parametric oscillators, which are the major tool for generating strong squeezing. 
In this talk I will present both a new homodyne measurement and a new generation scheme suitable for ultra-broadband squeezing; I will present a novel homodyne method for measuring optical bandwidth squeezing, demonstrating a measurement of more than 3dB squeezing over ~50THz bandwidth.  And I will present an intriguing new method for active mode-locking in a parametric oscillator, allowing the generation of broadband strongly squeezed light.

 

Guy Ron, HUJI
09/03/2016 - 16:20

Trapped radioactive atoms and ions have become a standard tool of the trade

for precision studies of beyond SM physics.  decay studies, in particular,

oer the possibility of detecting deviations from standard model predictions

of the weak interaction which signal new physics. These 'precision frontier'

searches are complementary to the high energy searches performed by the

LHC and other high energy/high luminosity facilities.

I will present a general overview of magneto-optical and optical traps and

their use for weak interaction studies. I will further present both the Berkeley

21Na trapping experiment and the new Hebrew University 17-25Ne trapping program, recent experimental results, and future plans.

1
 

Dr. Igor Rahinov, The Open University of Israel
02/03/2016 - 12:20

Understanding the atomic scale motion of chemical reactions occurring on metal surfaces has become an important topic of research, one that is motivated by its technological implications for heterogeneous catalysis. The importance of heterogeneous catalysis for humankind can hardly be overestimated. Its application range from pollution abatement to food industry. Unfortunately, even today, in most cases we are lacking detailed molecular level understanding of these processes.  Studies carried out under ultra-high vacuum conditions, with clean surfaces and with molecules in well-defined internal state distributions provide a wealth of information based on which a detailed microscopic view of the process can be constructed. In my talk I will refer to recent studies of  diatomics collisions with single crystal coinage metals studied by combination of molecular beams and laser spectroscopy, exemplifying how detailed studies of vibrational energy transfer, rotational and translational inelasticity can provide detailed insights into the dynamics of gas surface encounters. I will also cover another aspect of our work aiming towards gas-phase fabrication (chemical vapor deposition and flame assisted synthesis) of model functional surfaces and expanding the studies of gas surface interactions beyond single crystals to complex model catalysts.

Avi Peer
20/01/2016 - 12:00

Optical oscillators present a powerful optimization mechanism. The inherent competition for the gain resources between possible modes of oscillation entails the prevalence of the most efficient single mode. We harness this 'ultrafast' coherent feedback to optimize an optical  field in time, and show that when an optical oscillator based on a molecular gain medium is synchronously-pumped by ultrashort pulses, a temporally coherent multimode field can develop that optimally dumps a general, dynamically-evolving vibrational wave-packet, into a single vibrational target state. Measuring the emitted field opens a new window to visualization and control of fast molecular dynamics. The realization of such a coherent oscillator with hot alkali dimers appears within experimental reach.

Guy Bartal, Technion
13/01/2016 - 12:00

The ability to shape and focus optical waves to dimensions smaller than their wavelength has intrigued the scientific community both for its physical challenges and its potential applications. Resonant elements, , have provided deep-subwavelength control at long wavelength in the form of Metamaterials, while at optical frequencies light could be focused to specific points by nano-antenna and Nanofocusing elements, breaking the so-called diffraction limit. Alternatively,  achieving similar focusing dimensions by scaling the diffraction limit rather than breaking it allows flexible and dynamic control over the type and shape of the focusing without specifically patterning the medium, hence can provide super-resolution capabilities for bio-imaging, nanolithography and spectroscopy. We use the high refractive index of Silicon to scale the diffraction limit by  many-fold compression of the wavelength thereby achieving resolution at the order  of 10-s of nanometers at visible light. - Comparable to that of single-molecule microscopy techniques. Utilizing this scaled diffraction limit, we present phase-resolved near-field observations of propagating-waves bright and dark focusing below 70 nm at 671nm illumination (λ/10), and direct observation of short-wavelength Super-Oscillations in planar 2D Hybrid Silicon-plasmon waveguides.

Ofir Gabizon, University of Wuppertal
30/12/2015 - 12:00

After a two year shut down The Large Hadron Collider is finally back in business, 
and at a higher energy than ever before. First results from this year have just been published,
and next year much more data will be collected. The high energy frontier is just around the corner.
In the talk I will introduce the field of particles physics, and the experimental tools used to study it.
I will talk about the Large Hadron Collider, which has become the main device in particle physics 
to study the high energy frontier (Energies beyond 100GeV) . I will review the physics programme and goals behind it.
I will also show recent results which include possible hints for a new particle decaying to two photons (with an approximate mass of 750 GeV), which future data will support or refute.

I will end with hopes for the future.

Yonatan Israel, The Weizmann Institute
23/12/2015 - 12:00

Optical microscopy is a powerful tool, as it has been the workhorse of physical,
biological and medical research for over five centuries. Nevertheless, it is known 
that microscopy has some limitations. In this talk, I will show that two such major 
limitations can be overcome, namely improving the sensitivity and the resolution 
of standard optical microscopy, using quantum optical principles.

Conventionally, standard microscopy uses classical sources of light and simple 
cameras. By employing quantum light and quantum correlation
measurements, one can achieve sub-shot-noise imaging sensitivities and 
super-resolution beyond the diffraction limit, respectively.

Dr. Yoav Shechtman, Stanford University
16/12/2015 - 12:00

Super-resolution fluorescence microscopy has revolutionized the field of cellular imaging in recent years. Methods based on sequential localization of point emitters (e.g. PALM, STORM) enable imaging and spatial tracking at ~10-40 nm resolution, using visible light. Moreover, three dimensional (3D) tracking and imaging is made possible by various techniques, prominent among them being point-spread-function (PSF) engineering. The PSF of a microscope, namely, the shape that a point source creates in the image plane, can be modified to encode the depth (z position) of the source. This is achieved by shaping the wavefront of the light emitted from the sample, using a phase mask in the pupil (Fourier) plane of the microscope.
In this talk, I will describe how our search for the optimal PSF for 3D localization, using tools from information theory, led to the development of microscopy systems with unprecedented capabilities in terms of depth of field and spectral discrimination. Such methods enable fast, precise, non-destructive localization in thick samples and in multicolor; we have applied them to super-resolution imaging, tracking biomolecules in living cells and microfluidic flow profiling. Super localization microscopy holds great promise as a uniquely powerful tool for future measurements of nano-scale dynamics in living systems.

Yoel rak
09/12/2015 - 12:00

Upon the discovery of Australopithecus afarensis remains in the 1970s and the subsequent acknowledgment of the remains’ distinct taxonomic status, the new species was hailed as situated anatomically and chronologically “halfway” between an ape (the common ancestor of the chimpanzee and Homo sapiens) and modern humans. Furthermore, the primitive appearance displayed by A. afarensis, along with its age, rendered it an ideal link in the chain leading to modern human. 
Beginning in the 1990s, the intensive activity of numerous expeditions to the Hadar region of Ethiopia (site of the earlier A. afarensis finds, including the famous Lucy) and the discovery of two complete skulls, filled many gaps in our understanding of A. afarensis cranial anatomy and role of this species in human evolution. 

 

Dr. Nir Bar-Gill, The Racah Institute of Physics, Hebrew University
02/12/2015 - 12:00 - 13:00

Nitrogen-Vacancy (NV) color centers in diamond provide a unique nanoscale quantum spin system embedded in a solid-state structure. As such they are well suited for studies in a wide variety of fields, with emerging applications ranging from quantum information processing to magnetic field sensing and nano-MRI (Magnetic Resonance Imaging). Importantly, NVs possess unique optical transitions which allow for optical initialization and readout of their quantum spin state.

In this talk I will introduce the field of NV centers, and describe our research into understanding and controlling these systems, with the goal of enabling fundamental research and future applications.

I will present the techniques used for manipulation of the NV centers, and for enhancing their quantum coherence lifetime. Specifically, I will describe our recent work on extending the coherence time of arbitrary quantum states [1], and on spectrally characterizing the noise which limits coherence in shallow NVs [2]. I will then demonstrate how these approaches can be used for magnetic field sensing and nanoscale NMR (Nuclear Magnetic Resonance) and MRI. 


[1] D. Farfurnik et. al., PRB 92, 060301(R) (2015)

[2] Y. Romach et. al., PRL 114, 017601 (2015)

Dr. Yaron Bromberg
25/11/2015 - 12:00

Reciprocity is a universal principle that has a profound impact on
many areas of physics.  A fundamental phenomenon in condensed-matter
physics, optical physics and acoustics, arising from reciprocity, is
the constructive interference of waves which propagate along
time-reversed paths in disordered media, leading to, for example, weak
localization and the metal-insulator transition. Previous studies have
shown that such coherent effects are suppressed when reciprocity is
broken. In my talk I will present our recent experiment, in which we
have shown that by tuning a non-reciprocal phase we can coherently
control weak localization of light, also known as coherent
backscattering, rather than simply suppress it [1]. By utilizing a
magneto-optical effect, we controlled the interference between
time-reversed paths inside a multimode fiber with strong mode mixing,
observed for the first time the optical analogue of weak
anti-localization, and realized a continuous transition from weak
localization to anti-localization. In the last part of the talk I will
show how we can utilize the subtle interplay between reciprocity and
mode mixing in multimode fibers for secure optical communication [2].

 

[1] Y. Bromberg, B. Redding, S. M. Popoff, and H. Cao, Control of
coherent backscattering by breaking optical reciprocity,
arXiv:1505.01507.
[2] Y. Bromberg, B. Redding, S. M. Popoff, and H. Cao, Remote key
establishment by mode mixing in multimode fibers and optical
reciprocity, arXiv:1506.07892.

Dr. Eilon Poem,Department of Physics, University of Oxford
18/11/2015 - 12:00

Point defects in diamond are atomic-like systems embedded in a solid matrix. This combination enables the manipulation of light through light-matter interactions, as with isolated atoms, in addition to enabling spatial manipulations using photonic structures embedded into the solid matrix.  Specific examples include sources of quantum light, linear optical quantum gates, and quantum-optical memories (QOMs). In this talk I will focus on QOMs. These are key elements for the scaling-up of optical quantum information processing (OQIP), useful for both repeat-until success schemes of quantum computation, and for the synchronization of multiple photon events for the creation of large-scale quantum states of light, a required resource for OQIP. I’ll present our work towards the use of an ensemble of point defects in diamond for the controlled storage of quantum light. Based on previous work with atomic ensembles, I’ll explain the principles of such QOMs, and the adaptations needed for their implementation with two types of diamond defects. I’ll then present preliminary experimental results towards this goal.

Dr. Alon Bahabad, Department of Physical Electronics School of Electrical Engineering, Tel-Aviv University
10/11/2015 - 11:00

We consider possible applications of temporal superoscillatory optical signals. First we discuss the delivery of a super-oscillatory optical signal through a medium with an absorbing resonance at the super-oscillation frequency. While a regular signal oscillating at the absorption resonance frequency would be completely absorbed after a few absorption lengths, it is found that the superoscillation undergoes quasi-periodic revivals over optically thick distances. In the second part of the talk we present experimental results where the use of a superoscillating optical beat breaks the optical temporal   Fourier resolution limit by an unprecedented 75%. Such superoscillatory beats can substantially increase the temporal resolution of light-driven measurement and control processes. 

 

David Sarkisyan,Institute for Physical Research, NAS of Armenia, Ashtarak-2, 0203, Armenia
24/09/2015 - 12:00

The peculiarities of the Faraday effect (rotation of the plane of polarization of laser radiation in a magnetic field) are studied for the first time in the atomic vapors of the Cs and the Rb D1 lines using the nano- cells with the varying thickness L in the range of 20−900 nm. It is demonstrated that for the range of 100< L< 900 nm the Faraday rotation (FR) signal has a maximum for the highlighted thicknesses L= λ/2 = 448 nm (for the Cs) and 398 nm (for the Rb). Such type of peculiarities are absent for the common cells of centimeter-length. For the thickness L<100 nm the spectra of the FR demonstrate frequency “red shift” which gives evidence of the van der Waals (VW) effect. For the Rb atoms and L=60 nm (this is a record low L for FR observation) a giant frequency “red shift” of “-100 MHz” for the peak of the spectrum and of “- 400 MHz” for the low-frequencies-wing has been observed. For the atomic transitions VW coefficients C3 which characterize the atom-dielectric surface interaction were measured. The influence of the “recoil effect” which induces an additional “red shift” has been observed. 

Jonathan P. Dowling, Louisiana State University, Baton Rouge, LA
24/06/2015 - 12:00

  Over the past 20 years bright sources of entangled photons have led to a renaissance in quantum optical interferometry. These photon sources have been used to test the foundations of quantum mechanics and implement some of the spooky ideas associated with quantum entanglement such as quantum teleportation, quantum cryptography, quantum lithography, quantum computing logic gates, and sub-shot-noise optical interferometers. I will discuss some of these advances and the unification of optical quantum imaging, metrology, and information processing.

Erez Ribak, Technion
17/06/2015 - 12:00

In order to see single photoreceptor cells in the retina, we used hardware and software tools, getting close to the resolution limit, a tenfold improvement. Transparent layers which come in front of the photoreceptors are barely seen by direct imaging, but they play a major role in improving acuity. Radial cells of higher refractive index channel some colours directly into the corresponding photoreceptors to improve their responsivity. Other colours are scattered around, and serve for night vision. Finally, simulations and experiments explained the reason why the retina is inverted, with the photoreceptors behind the neural layers. 

Yoni Toker
10/06/2015 - 12:00

Human vision is based on a molecule, the retinal chromphore, which acts as an optical switch - following the absorption of a photon it undergoes an isomerization. This photoisomerization has remarkable properties - it is highly efficient, specific and fast. In order to understand this mechanism and photoisomerizations in general, we need a tool which allows us to 'see' the shape of an isolated molecule, and observe changes to the shape. These kinds of measurements have recently become possible thanks to developments in the field of ion mobility spectroscopy. In this talk I will survery the technique and present our recent study in which we measured the barrier energy for isomerization of the retinal chromphore. 

“Direct Measurement of the Isomerization Barrier of the Isolated Retinal Chromophore”, J. Dilger, L. Musbat, M. Sheves, A. B. Bochenkova, D. E. Clemmer, Y. Toker, Ang Chemie Int. Ed. 127 (2015), 4830-4834. 

Nathan Shammah (University of Southampton(
03/06/2015 - 12:00 - 13:00

In 1969 Mollow predicted that when a two-level quantum system is strongly pumped at resonance, it reemits light not only at its resonance frequency but also at two satellite frequencies. This result of quantum optics theory has been tested in many solid-state systems that can be described as two-level systems. We show that three peaks appear also when a two-dimensional electron gas confined in a quantum well is continuously pumped between two conduction subbands. Describing the resonance fluorescence with a many-body theory, we could go beyond the usual independent-dipole approximation. Remarkably, coherence in the electron gas can lead to a modified fluorescence spectrum. Moreover, with asymmetric quantum wells it is possible to engineer otherwise forbidden transitions, leading to a new tunable emission line, in the terahertz range.


BR Mollow, Phys Rev 188, 1969 (1969).
NS, CC Phillips and S De Liberato, Phys Rev B 89, 235309 (2014).

Yonatan Sivan, BGU
20/05/2015 - 12:00

One of the most fundamental nonlinear optical effects is the change of the refractive index of the material induced by light propagating in it. This effect is used in countless applications, most prominently, in modulations of semiconductor-based electro-optic components. These modulations are most frequently based on changing the free charge-carrier density. In this case, the modulation speed is limited by the natural pico-second to nano-second carrier recombination times. However, femto-second modulation times are required for many technological applications as well as for the study of various fundamental physics problems. 
Conventional approaches for shortening the carrier lifetime rely on material-science-based modifications of the material platform. In this talk I will introduce a different approach, based on novel ideas from wave physics, and on an aspect of the nonlinear response of free-carrier which was so far ignored – carrier diffusion, or the non-local nature of the free-carrier nonlinearity. We show that this effect becomes dominant when the free-carrier distribution has nano-scale features, e.g., in the case of transient Bragg gratings. 
Based on this phenomenon, I will show how we can easily achieve sub-picosecond modulation times in semiconductors and metals. I will review the complex analysis and numerics associated with this unusual regime of pulsed wave interactions and give a glimpse into the non-equilibrium dynamics of the hot charge-carriers. Finally, I will demonstrate several novel applications such as time-reversal and short pulse generation. 

 

Joseph Zyss,Laboratoire de Photonique Quantique et Moléculaire Institut d’Alembert, Ecole Normale Supérieure de Cachan, France
06/05/2015 - 12:00

The generic “billiard problem” is a well-known paradigm of nonlinear mathematical physics, which connects to deep issues in quantum and wave physics all the way to quantum chaos. It can be implemented in mechanics, optics or electromagnetism, either in classical or quantum mechanics, depending on experimental configurations and on the billiard length-scale. The elusive borders between wave and geometric optics on the one hand, and between quantum and classical mechanics on the other, exhibit deep analogies, which can be both addressed in actual billiard-like physical systems. We will show the relevance in this context of micro-billiard shaped lasers (1-4), thanks to new experimental and technological advances in the realm of polymer based photonics at micron and submicron scales. In such configurations, confinement of light in resonators can be considered by analogy with that of a quantum particle in a well (the 2-D quantum or wave billiard). Spatially distributed modes can be connected to classical orbits within the frame of semi-classical physics approximations, by use of the celebrated “trace theorem”, herein generalized to open and chaotic cavities. A beneficial feature of dielectric cavities, in contrast with their more investigated metallised contour counterparts, is the ability for the electromagnetic wave to spread-out of the cavity by refraction, diffraction, evanescent tunnelling or a combination of these, allowing to simplify the otherwise hidden physics and eventually lending itself to sensor applications. However, such “open cavities” are more challenging from a theoretical and modelling point of view, giving raise to non-Hermitian operators and imaginary eigenvalues accounting for a finite modal excitation life-time in lossy cavities. Analytical solutions such as available for the metallized 2-D rectangle are not valid for the equivalent open structures which demand to resort either to full-fledged solutions of the Maxwell-Helmholtz equations with continuity conditions on the contour, or to application of semi-classical orbit methods. We will show consistence between those two avenues and experimental findings. Particular attention will be paid to recent advances: systematic investigations of triangular cavities (5) and extension to 3-D micro-billiards (6). The role of contour singularities will be evidenced and the related diffractive orbits pin-pointed. The technological precision required for such studies is reached by advanced e-beam patterning methods applied to dye-doped polymer structures, down to the required nano-scale level of precision.
Our investigations illustrate an approach whereby, contrary to the more academic pathway from upstream mathematical predictions down to experimental applications, experimental findings may help provide guidelines towards otherwise elusive mathematical problems, such as the diffraction of light by a dielectric prism that the lasing property allows to illuminate from its inside. 
This is being performed at LPQM/ENS Cachan, together with Clément Lafargue (Ph.D. student), Stefan Bittner (postdoctoral) and Mélanie Lebental (assistant professor) within our “microlaser and nonlinear dynamics” research group.

 (1) Directional emission of stadium shaped micro-lasers, M.Lebental, J.S.Lauret, J.Zyss, C.Schmidt, E.Bogomolny, Phys. Rev. A 75, 033806 (2007)
 (2) Inferring periodic orbits from spectra of shaped micro-lasers, M.Lebental, N.Djellali, C.Arnaud, 
J.-S.Lauret, J.Zyss, R.Dubertrand, C.Schmit, E.Bougomolny, , Phys Rev. A, 76 023830 (2007).
 (3) Organic Micro-Lasers: A New Avenue onto Wave Chaos Physics, M.Lebental, E.Bogomolny and J.Zyss, Chapter 6, pp. 317-353 in “Practical Applications of Microresonnators in Optics and Photonics”, Andrey Matsko editor,(CRC Press, Boca Raton, 2009)
(4) Trace formula for dielectric cavities. II. Regular, pseudointegrable, and chaotic examples E.Bogomolny, N.Djellali, R.Dubertrand, I.Gozhyk, M.Lebental, C.Schmit, C.Ulysse and J.Zyss, Phys.Rev. E 83, 036208 (2011)
(5) Localized lasing modes of triangular organic microlasers, C. Lafargue, M. Lebental, A. Grigis, C. Ulysse, I. Gozhyk, N. Djellali, 
J. Zyss and S. Bittner, Phys.Rev.E 90, 052922 (2014)
(6) Three-dimensional organic microlasers with low lasing thresholds fabricated by multiphoton and UV lithography
Vincent W. Chen, Nina Sobeshchuk, Clément Lafargue, Eric S. Mansfield, Jeannie Yom, Lucas R. Johnstone, Joel M. Hales, Stefan Bittner, Séverin Charpignon, David Ulbricht, Joseph Lautru, Igor Denisyuk, Joseph Zyss, Joseph W.Perry and Melanie Lebental
Optics Express 22 (10), 12316-12326 (2014)

 

 

 

Or Katz
29/04/2015 - 12:00

Aklali vapor has long been a substantial tool in studying the atom-photon interactions in a well controlled environment, as well as the atom-atom interactions. The random spin-exchange collisions in warm alkali vapor are known to cause rapid decoherence, and act to equilibriate the spin state of the atoms. In this work we demonstrate experimentally that in contrast to the general concept of the collisions as a source of decoherence, a coherent coupling of one alkali specie (potassium) to another specie (rubidium) can be mediated by these random collisions.
Consequently, the potassium inherits the magnetic properties of the rubidium,
including its liftime (T1), coherence-time (T2), gyromagnetic ratio, and SERF magnetic field threshold. We further show that this coupling can be completely controlled by varing the strength of the magnetic field. Finally, we explain these phenomena analytically by modes-hybridization of the two species via spin-exchange collisions.

Dror Shafir
25/03/2015 - 12:00

The manufacturing of nanometric scale semiconductor structures in the chip industry requires extremely tight non-demolition process control. Modern transistors are about 10 nm wide - orders of magnitude smaller than the resolution limits of optical microscopes. Still, it is possible to tell whether a transistor is an angstrom too wide or too narrow using optical metrology tools. I will introduce Nova’s technology and describe the methods by which we can very precisely follow the chip fabrication process in real time.

 

Assaf Shaham
11/03/2015 - 12:00

Quantum decoherence is usually an unwanted effect, and efforts are made to minimize it. This is because it acts as an information noise that encumbers the realization of many quantum information schemes and protocols. It appears that creating such noise with well defined properties is also a hard task. We will present a way in which we apply such noise in a controllable way on quantum bits (qubits) encoded in the polarization of single photons. The implementation and the characterization of principal unital quantum channels such as dephasing and isotropic channels using birefringent crystals will be discussed. 

 

Applying the noisy channels to photon pairs, we were able to explore the quantum-to-classical transition of initial quantum states. We will elaborate on the ability of the photon pairs to exhibit entanglement or other quantum correlations such as nonlocality and contextuality in the presence of different types and levels of noise. Specifically, we will show that the generated initial states can exhibit quantum contextuality by violating the Klyachko-Can-Binicioğlu-Shumovsky (KCBS) inequality, and that the predicted hierarchy between quantum nonlocality and KCBS contextuality (i.e., KCBS contextuality implies nonlocality) is valid for states that experienced different types of decohering unital channels.

Dr. Aviv Ophir
04/02/2015 - 12:00

Exoplanetary transits are the periodic dimming of stars caused by the crossing of a black and opaque disk (the planet) in front of them". In this talk I will review many of the ways in which the former sentence is wrong: planets are neither opaque, nor non-luminous or disk-like, and transits may be neither color-neutral, constant in depth, duration or even have constant period. I will briefly describe how each and every one of these variations can tell us something about the planet and/or its system.I will then focus on the non-periodicity of planetary transits known as transit timing variations (TTVs). I will discuss its observational and dynamical origins, and show examples of the challenges and opportunities brought about by this new and exciting field of exoplanet studies, including new analytical tools and ground-based observational opportunities

Eugene Frumker
21/01/2015 - 12:00

Asymmetric molecules look and react differently when viewed from one side or the other.
This difference influences the electronic structure of the valence electrons,
thereby giving stereo sensitivity to chemistry and biology. I will show how the
attosecond and re-collision science provides a detailed and sensitive probe
of electronic asymmetry. I will demonstrate how a high-density gas can be oriented, report the first experimental observation of even and odd harmonics generated from oriented molecular samples and discuss the physical mechanism leading to orientation. The harmonic spectrum encodes three manifestations of asymmetry; an amplitude and phase asymmetry in electron tunneling; an asymmetry in the phase that the electron wave packet accumulates relative to the ion between the moment of ionization and recombination; and an asymmetry in the amplitude and phase of the transition moment.  The sensitivity of the high harmonic spectrum to subtle phase differences will drive major advances in the theory of high harmonic generation and give us detailed insight into the molecule itself

 

Avishay Eyal
14/01/2015 - 12:00

Distributed Acoustic Sensing (DAS) has been attracting considerable amount of attention in recent years for various applications including intrusion detection, railroad monitoring, pipeline protection, seismic profiling, oil and gas well monitoring, underwater acoustic sensing and more. In many such applications sub-meter spatial resolution is necessary in order to allow accurate sampling of the acoustic phase front at high frequencies. For instance, acoustic waves in water propagate at a typical velocity of ~1.5 km⁄s  , which means a wavelength of ~15cm for a frequency of 10KHz. All current implementations of DAS are based on fiber-optic reflectometry. Most DAS methods obtain the position information from the time delay of the backscattered signal. The spatial resolution in these methods is determined by the duration of the interrogating pulse. Hence, as in Optical Time-Domain Reflectometry (OTDR), there is a fundamental inherent tradeoff between the spatial resolution and the Signal to Noise Ratio (SNR). Typical OTDR based DAS systems have spatial resolution of ~10m or more. In contrast our approach is based on Optical Frequency Domain Reflectometry (OFDR). OFDR is a well-established method for measuring the reflection profile of an optical fiber. The method is based on transmitting, into the fiber, light whose instantaneous frequency varies linearly with time. The backscattered light from the fiber is then mixed with a reference and detected. The detector output (the beat signal) is Fourier-transformed to yield spatial information. In contrast with time domain reflectometry, OFDR enables excellent spatial resolution alongside with high SNR. In the talk I will describe the various approaches for implementing DAS and some of our work on the development and characterization of OFDR based DAS.

 

Prof. Koby Rubinstein, Faculty of Mathematics, Technion
07/01/2015 - 09:00

Freeform optical design concerns optical elements that have no apriori symmetry. I shall present a few concepts  in this area, both in imaging and nonimaging optics. I shall illustrate these concepts via several examples, including novel measurement devices, beam shaping lenses and adjustable spectacles.

Eliyahu Shwartz
31/12/2014 - 12:00

The nonlinear interactions between X-rays and optical radiation were first described about forty years ago by Freund & Levine [1] and by Eisenberger & McCall [2]. These studies addressed several nonlinear processes including parametric-down conversion of X-rays into the optical region, sum and difference-frequency generation of X-rays and optical pulses. However, until very recently there was no experimental evidence for any of those effects due to the absence of sufficiently bright X-ray sources. Recently, the new X-ray free-electron lasers have enabled the observation of X-ray and optical frequency mixing [3]. 
A new development in X-ray free-electron lasers has opened the possibility to generate two X-ray ultrashort pulses at different central wavelengths, with controllable delay between them. Motivated by this development, we studied the generation of short optical pulses from the X-ray pulses via the process of difference-frequency generation. We found that since the X-ray damage threshold is much higher than the optical damage threshold, the efficiency of difference-frequency generation from two X-ray pulses is orders of magnitude higher than the efficiency of frequency mixing between X-rays and optical intense short-pulses. Moreover, we show that the effect can be used for microscopic studies of chemical bonds and as a probe for light-matter interactions on the atomic scale and with temporal resolution on the order of 10 fs with the current performances of X-ray free-electron lasers. 
References and links
1.    I. Freund and B. F. Levine, “Optically modulated X-ray diffraction,” Phys. Rev. Lett. 25(18), 1241-1245 (1970).
2.    P. M. Eisenberger and S. L. McCall. “Mixing of X-ray and optical photons,” Phys. Rev. A 3(3), 1145-1151 (1971).
3.    T. E. Glover, D. M. Fritz, M. Cammarata, T. K. Allison, Sinisa Coh, J. M. Feldkamp, H. Lemke, D. Zhu, Y. Feng, R. N. Coffee, M. Fuchs, S. Ghimire, J. Chen, S. Shwartz, D. A. Reis, S. E. Harris and J. B. Hastings, “X-ray and optical wave mixing,” Nature 488(7413), 603-608  (2012).

 

Hagay Shpaisman,Chemistry Department & Institute for Nanotechnology, Bar-Ilan University, Israel
24/12/2014 - 12:00

During the last decade significant advances in controlling nano objects and polymer/DNA clusters with optical traps have been demonstrated along with the ability to create various phase changes induced by photon pressure. Here we present a novel method were colloidal particles are created when an optical trap is introduced while an emulsion polymerization is taking place. Nucleation seeds, oligomers and micelles are attracted to the trap and (under certain parameters) can coalesce or partly fuse before final polymerization, creating spherical or rod like colloids. Furthermore, we can create organic/inorganic colloidal hybrids if inorganic nanoparticles (NP) are introduced to the organic system undergoing polymerization while optical traps are present. Via a physical absorption process these nanoparticles are incorporated in the growing colloidal particle.

These methods hold great promise for creating on demand tailor made colloidal systems where size, shape and composition could be precisely controlled. The versatility and ease of making various changes to the end product without the need for chemical modifications (as the optical trap influences any material with higher polarizability than the surrounding medium) makes this approach appealing for testing model systems.

 

Dr. Ofer Firstenberg
10/12/2014 - 12:00

Realizing and engineering optical non-linearity at the level of single
photons is a goal of scientific and technological significance. We obtain
strong interactions between propagating photons by coherently coupling them
to Rydberg atoms in a cold gas. While slowly traversing the medium, the
"Rydberg polaritons” interact via the Van-der-Waals force, owing to their
large electric dipole-moment. We are able to vary the dynamics of the
two-photon wavefunction from dispersive (Schrodinger-like) to dissipative
(diffusion-like) and observe strong bunching, anti-bunching, and a
conditional phase-shifts of 1 radian for two individual photons.

Avi Peer
03/12/2014 - 12:00

Quantum squeezing - the reduction of noise fluctuations below the shot-noise limit in one quadrature of the light at the expense of amplified noise in the other quadrature - offers great opportunities for precision measurement and  quantum information. Current detection methods for quantum squeezing are unfortunately limited by detectors bandwidth, allowing experimental access only to narrowband squeezing. I will describe our efforts to develop broadband detection schemes for quantum squeezing and to exploit it in quantum measurement. I will specifically describe how classical methods from the RF domain can inspire quantum detection using the optical nonlinearity as the physical correlation detector 

Elad Yom-Tov
26/11/2014 - 12:00 - 13:00

Answering questions of health and medicine frequently necessitates the collection of data from large cohorts during real-world interactions. This is costly and, in many cases, extremely challenging due to the nature of these interactions and the difficulty in getting people to report about them. Work in recent years has shown that data generated by people as they browse the Web, including queries submitted to Internet search engines, social media postings, and even merely browsing histories can be used to learn about peoples’ activities in the virtual as well as the physical worlds. Therefore, these data could potentially serve as a cheap alternative for real-world data.
In this talk I will show that specific types of Internet data are less influenced by reporting biases, and are thus a low-cost alternative for extracting medical information from very large populations. I will discuss areas where Internet data are especially advantageous for addressing questions of health and medicine, and how these data can be coupled with other information in a privacy-preserving manner to improve the range of questions we can answer. I will illustrate with several recent examples such as post-market drug surveillance, discovery of a link between medial portrayal of underweight models and the development of anorexia, and the prediction of mood disorder events.

Alex Retzker
19/11/2014 - 12:00

The signal to noise ratio of quantum sensing protocols scales with the square root of the coherence time. Thus increasing this time is a key goal in the field.  By utilising quantum error correction, I will present a novel way of prolonging such coherence times beyond the fundamental limits of current techniques. I will present an  implementable sensing protocol that incorporates error correction, and discuss the characteristics of these protocols in different noise and measurement scenarios. The use of entangled vs. unentangled states, and error correction's reach of the Heisenberg limit will be discussed

Prof. Avi Zadok, Faculty of Engineering, Bar-Ilan University
12/11/2014 - 12:00 - 13:00
The analysis of stimulated Brillouin scattering (SBS) interactions along optical fibers is being used in the distributed sensing of temperature and strain for 25 years. SBS is maximal when the difference between the optical frequencies of two counter-propagating waves, a pump and a signal, matches the Brillouin frequency shift of the fiber. The Brillouin shift, in turn, varies with both temperature and strain. Distributed sensing is based on the reconstruction of the position-dependent Brillouin gain spectrum along the fiber.  
In Brillouin optical time-domain analysis (B-OTDA), an intense pump pulse is used to amplify a counter-propagating continuous-wave (CW) signal, and the output signal power is monitored as a function of time. The spatial resolution of the fundamental B-OTDA configuration is restricted to the order of 1 m by the SBS lifetime of about 5 ns. Numerous schemes have been proposed and demonstrated for B-OTDA resolution enhancement. State-of-the-art B-OTDA had reached 2 cm resolution over a measurement range of 2 km. Higher resolution was obtained using the complementary technique of Brillouin optical correlation domain analysis (B-OCDA). B-OCDA relies on the close relation between the strength of the Brillouin interaction at a given location, and the temporal cross-correlation between the complex envelopes of the pump and signal waves at that point. State-of-the-art frequency-modulated B-OCDA reached mm-scale spatial resolution, and 24,000 resolution points.In this seminar, I review several advances in B-OCDA, and in the combination of B-OTDA and B-OCDA, which were proposed and demonstrated by our group and collaborators over the last two years. These include the modulation of continuous pump and signal by a binary phase sequence; the employment of specialty sequences known as Perfect Golomb Codes; a hybrid B-OTDA / B-OCDA setup, in which a pulsed pump and a continuous signal are jointly modulated by periodic phase sequences; and the extension of the pump wave amplitude modulation to long sequences with particularly low correlation sidelobes. Using these methods, Brilloin analysis is performed over a 4 km-long fiber with 2 cm resolution, and the entire set of over 200,000 points is interrogated. 
Nir Kampel
29/10/2014 - 12:00

Observing and Evading Quantum Backaction in an Interferometer 
N. S. Kampel, T. P. Purdy, P.-L. Yu, R. W. Peterson, and C. A. Regal


The pursuit to eliminate classical noise sources in an interferometer has a long history. Only recently have experimental conditions matured enough to enable measuring quantum backaction in the continuous displacement detection of a solid mechanical resonator. Moreover reaching the regime in which mechanical vacuum fluctuations dominate opens the door to variety of experiments, from ultra-high position and force sensitivity to producing mechanical quantum states.
We use a macroscopic silicon nitride membrane resonator in a high-finesse optical cavity to measure the quantum backaction put forth by a light probe. Here I present initial results of two experiments. In the first we avoid the quantum backaction, and in the second we measure evidence of the resonator being in the quantum mechanical ground state.

David J. Bergman,Raymond and Beverly Sackler School of Physics and Astronomy Faculty of Exact Sciences,Tel Aviv University
25/06/2014 - 12:00

The resolution of conventional optical lenses is limited by the wavelength. Materials with negative refractive index have been shown to enable the generation of an enhanced resolution image where both propagating and non-propagating waves are employed. We analyze such a Veselago lens by exploiting some exact one dimensional integral expressions for the quasi-static electric potential of a point charge in that system. Those were recently obtained by expanding that potential in the quasi-static eigenfunctions of a three-flat-slabs composite structure. Numerical evaluations of those integrals, using realistic values for physical parameters like the electric permittivities of the constituent slabs and their thicknesses, reveal some surprising effects: E.g., the maximum concentration of the electric field occurs not at the geometric optics foci but at the interfaces between the negative permittivity slab and the positive permittivity slabs. The analysis provides simple computational guides for designing such structures in order to achieve enhanced resolution of an optical image.

David Sarkisyan,Institute for Physical Research, NAS of Armenia, Ashtarak-2, 0203, Armenia
18/06/2014 - 12:00

The implementation of recently developed technique based on narrowband laser diodes, strong permanent magnets and micro-and nano- thin optical cells make studies of the atomic transitions behavior in an external strong magnetic field  simple and robust [1,2].

            Particularly, the magnetic field-induced giant modification of probabilities for seven components of 6S1/2, Fg = 3 → 6P3/2, Fe = 5 atomic transition of the Cs D2 line, forbidden by selection rules (at zero magnetic field), is observed experimentally for the first time. The applied theoretical model describes very well the experimental curves [3].

            So called Hyperfine Paschen Back (HPB) regime has been demonstrated for the Potassium atoms (for the first time) in the presence of strong magnetic field. Important and striking peculiarities of HPB regime for Potassium atoms observed with the help micro-and nano- thin optical cells will be presented.

 

References

[1] A.Sargsyan,A.Tonoyan,R.Mirzoyan,D.Sarkisyan, A.Wojciechowski,W.Gawlik, Optics Letters, 39, 2270 (2014).

[2] A. Sargsyan, G. Hakhumyan, R. Mirzoyan, D.Sarkisyan, JETP Letters 98, 441(2013).

[3] A Sargsyan, A Tonoyan, G Hakhumyan, A Papoyan, E Mariotti, D. Sarkisyan, Laser Physics Letters, 11  , 055701 (2014).

 

Paul Brumer Department of Chemistry and Centre for Quantum INformation and Quantum Control University of Toronto
21/05/2014 - 12:00

2D photon echo studies on light harvesting systems
have generated considerable interest and controversy regarding 
the possible role of quantum coherence effects in biological systems.
As we have previously shown, such studies rely on the response of
molecular systems to pulsed laser excitation, which is 
dramatically different than the response to natural incoherent
light. Significantly, the latter produces mixed stationary states,
devoid of time dependent coherences. If this would be ``the whole 
story", then the observed coherences are essentially irrelevant.

We will describe the origin of the above result and then discuss recent
developments in this area, including (a) the importance of various 
decoherence time scales for reaching stationary states in natural incoherent
light, (b) the role of doorway states in the molecular response, and (c) the
significance of long lived coherences associated with Agarwal-Fano resonances.
Examples will be chosen from basic three level V-systems,
dynamics in large molecules, and Rydberg atoms
interacting with the cosmic microwave background. The significance of the
results for natural light harvesting systems will be emphasized.

Shamir Rosen
14/05/2014 - 12:00

A quantum polarized light microscope using entangled NOON states with N = 2 and N = 3 is
shown to provide phase super-sensitivity beyond the standard quantum limit. We constructed such
a microscope and imaged birefringent objects at a very low light level of 50 photons per pixel, where
shot-noise seriously hampers classical imaging. The NOON light source is formed by combining a
coherent state with parametric down converted light. We were able to show improved phase images
with sensitivity close to the Heisenberg limit.

Nimrod Moiseyev
07/05/2014 - 12:00

   In high frequency strong laser fields the oscillating electrons in an atom behave like they are moving not in a field induced by a positive point charge of the nucleus but in a field which is smeared along the  polarization direction of the light and it is peaked at +/- of the quiver length (defined as the ratio between the maximum field amplitude and the square of the laser frequency multiplied by the mass of the electron). 
We show that for many electron atoms (such as sulfur and oxygen) the ground state of the laser dressed atom has a long lifetime and can be degenerated. Hence, a strong linear Stark effect rather than the usual quadratic one is obtained. 
We show that also a new type of chemical reactions is induced by the high frequency strong laser fields. For example, strong chemical bond (dissociation energy is more than 12 eV) is generated between two helium atoms with a bond length of 2 Angstroms. Similarly a strong chemical bond is created between sulfur and helium atoms which is somehow similar in its nature to the chemical bond in OH radicals.

  P.  Balanarayan and N. Moiseyev, "Strong chemical bond of stable He2 in strong linearly polarized laser fields", Phys. Rev. A 85, 032516 (2012).
P.  Balanarayan and N. Moiseyev, "Chemistry in high-frequency strong laser fields: the story of HeS molecule", Mol. Phys. 111, 1814 (2013).
  P.  Balanarayan and N. Moiseyev, "Linear Stark effect for sulfur atom in strong high frequency laser fields", Phys. Rev. Lett. 110, 253001 (2013).

Gennady Koganov
30/04/2014 - 12:00

The first model of stationary superradiance, the superradiant laser, was suggested by Haake et al. [1]. Since then, several theoretical papers discussing this scheme, as well as some other models, have been published [2]. The key mechanism responsible for stationary superradiance in such lasers is the collective nonlinear spontaneous decay of one of the atomic states that is imposed by an additional, ”passive” resonator. As we have shown recently [3], the super/subradiant lasing can be obtained by replacing the passive resonator by a second coherent pumping laser field, so that no initial atomic cooperativity is required. In this talk the results of semiclassical treatment of a three-level ladder model of super/subradiant laser will be discussed in details.
[1] F. Haake, M. I. Kolobov, C. Fabre, E. Giacobino, and S. Reynaud, Phys. Rev. Lett. 71, 995 (1993).
[2] F. Haake et al, Phys. Rev. A 54, 1625 (1996); I. E. Mazets and G. Kurizki, J. Phys. B 40,
F105 (2007); C. Wiele et al, ibid, 60, 4986 (1999); D. Yu and J. Chen, ibid, 81, 053809 (2010).
[3] G.A. Koganov and R. Shuker, Opt. Lett. 36, 2779 (2011).

Yoav Linzon
02/04/2014 - 12:00

We performed in-situ sensing of volatile droplet and spray liquid mass using plate-like micro-resonator plates with low compressive stress, where robust and reusable operation over harsh conditions and multiple cycles was proven. A home-built electro-optical motion sensing system in ambient conditions was been used. The bimorph effects on the resonant frequency of altered mass loading, elasticity and strain have been compared, and the latter were found to be negligible in the presence of non-viscous liquids deposited on top of the devices. In resonant mode, the loaded mass is estimated from measured resonant frequency shifts and interpreted from simple (uniformly deposited film) model.

A minimum sub-ng detectable mass has been estimated, suggesting the potential for fast and reusable sensing capabilities of volatile liquids under harsh operation conditions.
We also describe very efficient parametric actuation in electro-statically excited single-layer microresonators, which can be employed in future integrated surface material sensors (for both liquid and vapor environments)
 
Ref:s     [1] submitted, IEEE Journal of Selected Topics in Quantum Electronics special issue on optically based sensors (2014)
            [2] J. Appl. Phys. 113, 163508 (2013)
 

Yoav Sintov
26/03/2014 - 12:00

The limitations of high power single mode fiber lasers such as stimulated Raman scattering, thermal lensing and modal instabilites are presented. In order to scale-up the power from high beam quality fiber laser sources, incoherent beam combinging is being employed, yielding a kWatt scale high brightness source .

Jacob (Koby) Scheuer
19/03/2014 - 12:00

We demonstrate wide-angle, broadband and efficient reflection holography by utilizing coupled dipole-patch nano-antenna cells to impose an arbitrary phase profile on of the reflected light. High fidelity images were projected at angles of 450 and 200 with respect to the impinging light with efficiencies ranging between 40%-50% over an optical bandwidth exceeding 180nm. Excellent agreement with the theoretical predictions was found at a wide spectral range.  The demonstration of such reflectarrays opens new avenues towards expanding the limits of large angle holography.

Pavel Chapovsky
12/03/2014 - 12:00

A setup for preparing the Bose–Einstein condensate of Rubidium atoms is described. The condensate consists of 105–106 87Rb atoms in the hyperfine state Fg = 2 of the ground electronic state. Three key indications of condensation, a sharp increase in the phase space density of atoms, the threshold emergence of two fractions in the cloud, and anisotropic expansion of the condensate, have been observed.

The future experiments with the Rubidium BEC are discussed. The plans are to create very cold samples using BEC and to study the properties of BEC at variable interatomic interactions.

Oren Cohen
05/03/2014 - 12:00

High harmonic generation is an extreme nonlinear process in which infrared or visible radiation is frequency up-converted into the extreme ultraviolet and x-ray spectral regions. As a parametric process, high harmonic generation should conserve the radiation energy, momentum and angular momentum. Indeed, conservation of energy, momentum and orbital angular momentum have been demonstrated. On the other hand, conservation of spin (polarization) angular momentum has thus far never been studied, neither experimentally nor theoretically.
 
I will present the first study on the role of spin angular momentum in extreme nonlinear optics. In our experiment, we generate high harmonics of bi-chromatic elliptically-polarized pump beams that interact with isotropic media. While observing that the selection rules qualitatively correspond to spin conservation, we unequivocally find that the process of converting pump photons into a single high-energy photon does not conserve angular momentum. In one regime, we find that this major discrepancy can be explained if the harmonic photons are emitted in pairs.

Yoav Sintov
26/02/2014 - 12:00
TBA

TBA

David Avisar
15/01/2014 - 12:00

Understanding the mechanisms of chemical reactions is a central goal of chemistry. Most photochemical reactions occur in excited electronic states and are governed by the excited potential energy surface. Except for very small molecules it is extremely challenging to know these potentials with any reasonable accuracy. 
We have recently shown that one can reconstruct the complete excited-state wavefunction (WF) of a reacting molecule [1,2]. Generally, WF reconstruction methods require a priori knowledge of the excited potential [3,4]. The WF reconstruction methodology we propose uses no a priori information on any excited state, but only of the ground state. We express the excited-state WF in the basis of the (assumed known) ground vibrational eigenstates. The superposition coefficients can then be extracted by inversion of a multi-dimensional CARS signal. The method applies to polyatomics, and to dissociative as well as bound excited potentials. Finally, the unknown excited potential can be recovered from the excited WF.

 

[1] D. Avisar and D.J. Tannor, PRL, 106, 170405, (2011).

[2] D. Avisar and D.J. Tannor, JCP, 136, 214107, (2012).

[3] M. Shapiro et al, PCCP, 12, 15760, (2010).

[4] J.A. Cina, Annu. Rev. Phys. Chem., 59, 319, (2008).

Klavs Hansen, Department of Physics, University of Gothenburg
01/01/2014 - 12:00

The separation of electronic and vibrational times scales opens the possibility that electronic matter in a highly excited incoherent state coexist for a short time with cold vibrations. During this short time, of a picosecond or less, the hot electrons can emit thermal electrons with extremely high temperatures from clusters and fullerenes.

Experiments on fullerenes and endoheral fullerenes with femtosecond laser pulses at deep sub-threshold photon energies will be presented. In the experiments electron energy distributions and ionic photo-fragmentation have been measured and analyzed in terms of this hot electron model.

Ephraim Shahmoon, Weizmann Institute of Science, Israel
25/12/2013 - 12:00

Dipolar interactions lay at the basis of a variety of phenomena in physics and chemistry, ranging from fundamental quantum vacuum forces and energy transfer all the way to emerging quantum technologies.  This work concerns the important possibility to drastically modify these dipole-dipole interactions, thus potentially affecting much of the above phenomena:  Since the interactions between dipoles are mediated by (virtual) photon modes, they can be enhanced by considering dipoles embedded in geometries that confine these modes. In this context, I will present our results on the possibilities for giant van der Waals and Casimir interactions via transmission lines, long-range deterministic entanglement and non-additive many-body physics with laser-induced interactions.

Boris Khaykovich
18/12/2013 - 12:00

Neutron scattering is a powerful suite of scientific tools for determining the structure and dynamics of matter. The technique is widely used in physics, materials science, biology, and engineering. National neutron scattering facilities are billion-dollar 
installations, serving hundreds of scientists per year. While modern light optical 
instruments use a variety of focusing devices (such as lenses and mirrors) and techniques (structural illumination, phase-contrast microscopy, etc), neutron instruments remain in the age of pinhole cameras. Were powerful optical tools available for neutron scattering, they might bring significant, even transformative, improvements to rate-limited neutron methods and enable new science. The MIT/NASA collaboration have recently pioneered the use of axisymmetric focusing mirrors, which have the potential of transforming neutron imaging and scattering instruments from pinhole cameras into microscopes. I will show how such reflecting lens could help increasing the resolution of neutron imaging and scattering instruments. (For a more extended introduction, see: http://www.materials360online.com/newsDetails/42202)

 

Barak Dayan
11/12/2013 - 12:00

I will present our progress towards the demonstration of a 1-atom based single-photon switch, utilizing cavity-QED with toroidal micro-resonators.
Practical single-photon switching, namely controlling the direction of one single-photon pulse with a control field that is another single-photon pulse, has not been achieved experimentally to date.
This device will also function as a 1-qbit quantum memory, enabling a deterministic quantum state transfer between a single photon and an atom, with no need for any control field.

 

Itai Afek
04/12/2013 - 12:00
Precise wind speed measurements at heights in the 0-200m range are crucial for the selection of appropriate sites for wind energy farms. Currently the industry depends on meteorological towers with mechanical and sonic, local, wind sensors. At Pentalum, a Rehovot based start-up, we have developed a remote sensing wind measurement LiDAR which allows measurement of the full vertical wind profile from a ground based device. Our technology is based on direct detection and correlations in contrast with the prevalent Doppler scheme.
In this talk, I will describe the basics of the direct detection technology and show some wind measurements from various sites around the world. I will also go into some physical / optical challenges we have encountered and discuss how we are addressing them.

 

Tal Carmon
27/11/2013 - 12:00

In 2005 we were reporting on the centrifugal radiation pressure of light as a new mechanism for actuating mechanical vibrations. Today I will describe our recent results in cooling via light-sound interaction and optical excitation of vibration at >10 GHz rates

 

Prof. Tal Carmon
27/11/2013 - 12:00 - 13:00

Prof.  Carmon has conducted a series of beautiful groundbreaking experiments on optomechanical effects in microshpere resonators.  His work includes the demonstration of interesting effects such as spontaneous Brillouin cooling, Brillouin cavity optomechanics with microfluidic devices and many more. He is a great speaker who uses basic intuition to describe his results. Note the attached picture. 

In 2005 we were reporting on the centrifugal radiation pressure of light as a new mechanism for actuating mechanical vibrations. Today I will describe our recent results in cooling via light-sound interaction and optical excitation of vibration at >10 GHz rates.

 

 

Lev Khaykovich
06/11/2013 - 12:00

In the early days of laser cooling of atomic gases, unexpectedly low temperatures were discovered in different laboratories across the world. A new cooling mechanism, called Sisyphus cooling, proposed by J. Dalibard and C. Cohen-Tannoudji, explained these findings and led later to Nobel Prize in physics awarded to C. Cohen-Tannoudji in 1997. Unfortunately, this elegant mechanism doesn’t apply for all atomic species used in ultracold atoms experiments. However, last year a beautiful extension of Sisyphus cooling has been realized exactly for those unfortunate species for which the usual mechanism fails to work. In my talk I will describe the mechanism, called “grey molasses”, and show the experimental results.

Leah Margalit
30/10/2013 - 12:00

In this talk, I will present our theoretical research on the effect of various magnetic fields (MFs) on the coherence spectra of alkali atoms. The chosen coherent process is Coherence Population Trapping (CPT) which has a wide range of applications. The MFs whose effects have been investigated are static (dc) and oscillating (ac) fields, longitudinal (LMF) and transverse (TMF) to the light propagation direction, as well as a combination of several types of magnetic fields.

 

The effect of the different MFs has been analyzed both analytically and numerically. I will discuss the contributions of the various subsystems to the total absorption spectra in each case. The different effects of LMF and TMF will be shown and some ways of measuring them will be suggested

Asaf Eilam
23/10/2013 - 12:00 - 13:00

 

Homo- chiral dimers (R - R) and (S - S) and hetero- chiral dimers (R - S) obey opposite selection rules, in regard to their dimer states. Based on that we proposed two simple schemes for purifying scalemic (not 50% - 50%) chiral mixtures.

The first scheme is based on the selective excitation of the target dimers by a single pulse. The second scheme is based on spatial separation of these dimers by a selective laser induced potential. This scheme is executed by a simple coherent control technique, which selectively subjects one of the dimers to a dark (null) potential while the other is subjected to a bright potential. I will present the theoretical background for the selective selection rules of the dimers, and explain the mechanism of selective potentials

Amir Capua, Electrical Engineering, The Technion
26/06/2013 - 12:00 - 13:00

Observation of coherent quantum light matter interactions requires that in the medium where the interaction takes place, the de-phasing time is much longer than the time needed for the observation.

In semiconductors, the de-phasing time is determined by scattering processes; at room temperature, it is about 1 ps. Therefore, experiments which probe coherent phenomena are always done at cryogenic temperatures. However, it is also possible, in principle, to sufficiently shorten the observation time so that it is not required to cool the material. This is the approach we have taken in this work which resulted in a direct observation of Rabi oscillations and self-induced transparency in a room-temperature semiconductor laser amplifier.

In this talk I will start by describing an investigation of the dynamical response of InAs/InP nanostructured quantum-dot and quantum-dash (wire-like) gain media following a perturbation of a short 150 fs pulse. In order to study the inhomogeneous nature of the gain broadening, we used a unique ultrafast multi-wavelength pump-probe setup. We then further increase the temporal resolution of our observation up to a few femtoseconds by using a highly sensitive FROG (Frequency resolved optical gating) setup which is capable of measuring the complete electro-magnetic field (phase and amplitude) of the short pulse after propagation. The work is accompanied by an extremely general numerical model of the Maxwell and Schrödinger equations describing the co-evolution of the electronic wavefunction together with the electro-magnetic field and has great novelty in its own right.

With these experimental and theoretical tools we have discovered a novel two-photon induced instantaneous gain mechanism that is also capable of initiating laser oscillations and identify a cascaded four wave mixing process induced of short pulses propagating within a laser. The highlight of the work is the direct observation of the co-evolution of the electronic wavefunction in the semiconductor together with the electro-magnetic field with a nearly single femto-second resolution. These are revealed in the form of Rabi oscillations and self-induced transparency, all occurring at room temperature and at the important optical-communication wavelength of 1.55 um. 

Shlomi Kotler, Weizmann Institute of Science
12/06/2013 - 12:00 - 13:00
Spectroscopy was a key player in the emergence of experimental Quantum Information Processing. Spectroscopic tools, built on the abilities to isolate and coherently manipulate trapped atomic particles, were used to create Bell pairs, store quantum information for seconds and release it.
In the past few years, spectroscopy had a surprising return on investment. It turns out that the same techniques that are used to generate entanglement are also useful for precision spectroscopy. So useful, in fact, that the best atomic clock to date is based on quantum information techniques.
It is this interesting turn of events that will be the focus of our talk. We will show in theory and experiments how one can use non-commutativity of quantum mechanical operators to enhance spectroscopic measurements. With these techniques we achieved the best magnetic field measurement sensitivity for a single spin (15 pT/√Hz) as well as the detection of the magnetic interaction of two electrons.
 
Ron Folman, Ben-Gurion University of the Negev, Israel
05/06/2013 - 12:00 - 13:00
The splitting of matter-waves into a superposition of spatially separated states is a fundamental tool for studying the basic tenets of quantum mechanics and other theories, as well as a building block for numerous technological applications.
I will describe the realization of a matter-wave beam splitter based on magnetic field gradients on an atom chip, which can be used for freely propagating or trapped atoms in a Bose-Einstein condensate or a thermal state. The beam splitter incorporates several fundamental quantum processes such as Rabi Oscillations, Ramsey fringes, first and second order Zeeman splitting and Stern-Gerlach interactions.
As the beam splitter is “classical” in the sense that it is run by classical currents, it is interesting to see how far can technology take us in terms of coherence or more precisely, in terms of phase and momentum stability. I will describe the current situation as well as what are the fundamental limits.
The beam splitter has a wide dynamic range of momentum transfer and operation time. Differential velocities exceeding 0.5 m/s can be achieved in a few microseconds. It may enable a wide range of applications, such as, fundamental studies of many-body entanglement and dephasing processes, probing classical and quantum properties of nearby solids, and metrology of rotation, acceleration and gravity on a chip scale.
 
S. Machluf et al., arXiv:1208.2526 (2012).
Dr. Tal Ellenbogen, Department of Physical Electronics, School of Electrical Engineering, Tel-Aviv University
29/05/2013 - 12:00 - 13:00

Recent years have seen enormous advancements in the precise fabrication capabilities of micro- and nano-sturctures which led to the emergence of the exciting field of nanophotonics. This is due to the fact that the optical properties of nanostructured materials can be engineered and the interaction between light and matter is strongly affected by encapsulating photons in such structures and materials.  

In my talk I will present some examples of light manipulation by exploiting strong interactions in micro- and nano-structures. I will show how a leaky planar optical waveguide doped with excitonic gain material acts as an optical antenna which radiates quasi-coherent cylindrical vector beams. I will then show that by increasing the oscillator strength of the excitonic material strong coupling between waveguide photons and excitons can be observed. This changes the dynamics of the coupled system and splits its eigenmodes into mixed photon-exciton modes which share properties of light and matter. Finally I will present the development of tunable plasmonic color filters based on the excitation of localized surface plasmons in unique optical nano-antennas and show some of their applications.

 

website: www.eng.tau.ac.il/~tal/neolab

 

Avi Niv, the Faculty of Electrical Engineering, Technion
22/05/2013 - 12:00 - 13:00

 

In this seminar I will review my current research activity and interests. These can be roughly divided into two: Energy, and basic light-matter interaction. On the energy front I will describe recent attempt to combine non-equilibrium thermodynamics with electromagnetics. This research is motivated by the need to find the limiting efficiency of devices whose optics cannot be considered under the approximation of rays. Among such devices are conceptual solar cells that incorporate light management techniques form the realm of nano- and metal-optics. On the second front, namely basic light-matter interaction, I will describe for the first time in public what I believe to be a groundbreaking approach to synthetic nonlinear activity in metal-dielectric composites. This research aims at stronger nonlinear activity with immediate emphasis on second order processes such as sum and difference frequency generation.

Shai Yefet, Bar Ilan University
08/05/2013 - 12:00 - 13:00

I will describe theoretical and experimental studies of mode-locked solid-state lasers, specifically a Kerr-lens mode-locked Titanium:Sapphire laser. This laser is the major source for ultra-short optical pulses, which provides an extremely important tool to investigate ultra-fast processes in physics, chemistry and biology. Specifically, I will present novel cavity designs and configuration, which overcome many of the disadvantages and inherent limitations of standard designed Ti:sapphire optical cavities.

Nadav Katz, The Racah Institute of Physics, Hebrew University in Jerusalem
01/05/2013 - 12:00 - 13:00

Several experiments will be presented and discussed:

1. Control of vortex array rotation and motion in electromagnetically induced transparency. We demonstrate how the classical optics effect of near-field vortex rotation is modified by the tunable media susceptibility.

2. Phase modulation spectroscopy in EIT media - we measure the electromagnetically induced transparency transmission for a probe with a strongly phase-modulated pump, demonstrating a transition from adiabatic to non-adiabatic response, along with magnetic field dependence.

3. Prospects for single/single photon memory experiments in this system 4. Diffraction from an AC stark-shifted grating of the Rb atoms in the cell.

5. Briefly: Birefringent magnetometry measurements in the SERF regime (high density, high collision rate regime).

Dr. Patrick Sebbah, Institut Langevin in Paris, France,
24/04/2013 - 12:00 - 13:00

 I will introduce the concept of random laser. As an illustration, I will present an innovative mirrorless optofluidic random laser where the optical cavity has been replaced by a random scattering structure. This device serve to show that control can be regained on the random lasing emission. We achieve emission control at any desired wavelength by iteratively shaping the optical pump profile.

Prof. Gil Markovich, School of Chemistry at Tel Aviv University
17/04/2013 - 12:00 - 13:00

I will describe several systems where plasmonic or excitonic nanostructures interact with chiral molecules and circular dichroism (CD) appears in the plasmonic or excitonic resonances.

In particular: the enhancement of CD using plasmonic nanostructures interacting with small quantities of chiral molecules will be described. Size and material dependent study of induction of CD in exciton transitions in colloidal semiconductor quantum dots as a tool to learn on the mechanism of the interaction of the molecules with the dots and about the exciton states. Finally, I will discuss the synthesis and chiroptical properties of nanostructures made of intrinsically chiral materials.

Prof. Peter Halevi, Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), Tonantzintla, Puebla 72000, Mexico
10/04/2013 - 12:00 - 13:00

Thousands of papers were published about photonic crystals, namely artificial composites with spatial periodicity. In this talk I will explore the properties and possible realization of temporal photonic crystals (TPCs) with periodicity in time. Specifically, I assume that either the permittivity and/or permeability of a (spatially uniform) medium is a periodic function of time. This gives rise to interesting behavior such as parametric resonances that depend on the thicknes of the dynamic slab and to pulse transmission with faster-than-light partial pulses (that correspond to harmonics of the modulation frequency). Finally, I will show that TPCs can be realized in the microwave regime by means of transmission lines with capacitors (varactors) and/or inductors that are temporally periodic.
 
 

Prof. David Tannor, Department of Chemical Physics, Weizmann Institute of Science
03/04/2013 - 12:00 - 13:00

 

In 1946, Gabor proposed using a lattice of  Gaussians in the time-frequency phase space to provide an intuitive and compact representation of arbitrary signals. The same idea had actually been discovered fifteen years earlier by his countryman von Neumann, in searching for a way to represent arbitrary quantum mechanical wavefunctions in the position-momentum phase space.  Despite the great interest in this approach in both the signal processing and quantum mechanical communities, the method has never succeeded as hoped due to severe convergence problems.  We have recently discovered a simple and surprising solution to the convergence problem, based on introducing periodic boundary conditions into the Gabor/von Neumann lattice. The resulting method provides a simple and compact representation of arbitrary signals and images, and opens the door to unprecedentedly large quantum calculations based on exploiting the underlying classical phase space structure. In the classical limit the method reaches the remarkable efficiency of 1 basis function per 1 eigenstate. We illustrate the method by calculating the vibrational eigenstates of a polyatomic with 104 bound states and by simulating attosecond electron dynamics in the presence of combined strong XUV and NIR laser fields. We also present examples of audio and image compression where we show that the method is competitive with or superior to state-of-the-art wavelet methods.

 

1. A. Shimshovitz and D. J. Tannor, Phase Space Approach to Solving the Time-independent Schrödinger Equation, Phys. Rev. Lett. 109, 070402 (2012).

2. N. Takemoto, A. Shimshovitz and D. J. Tannor, Phase Space Approach to Solving the Time-dependent Schrödinger Equation: Application to the Simulation and Control of Attosecond Electron Dynamics in the Presence of a Strong Laser Field, J. Chem. Phys. 137, 011102 (2012) (Communication).

3. A. Shimshovitz and D. J. Tannor, Phase Space Wavelets for Solving Coulomb Problems, J. Chem. Phys. 137, 101103 (2012) (Communication).

4. A. Shimshovitz and D.J. Tannor, Periodic Gabor Functions with Biorthogonal Exchange: A Highly Accurate and Efficient Method for Signal Compression, IEEE Signal Processing (submitted);  arXiv:1207.0632 [math:FA]

Dr. Yoni Toker, Institute of Physics and Astronomy, Aarhus University, Denmark
20/03/2013 - 12:00 - 13:00

 

Dr. Y. Toker / Institute of Physics and Astronomy, Aarhus University, Denmark

*current Address: Department of Particle Physics, The Weizmann Institute of Science

 

Biochromophores are the molecules used by living organisms in order to interact with visible light. Naturally these molecules are found within proteins, however in order to arrive at a fundamental understanding of their basic properties, our approach is to study the chromophores isolated from their surroundings using action spectroscopy. Recent photo-electron spectroscopy measurements of the Green Flourescent Protein chromophores will be presented, revealing and interesting competition between the different quantum paths available to the chromophore after photo-excitation; as well as photo-fragmentation studies of the Retinal chromophore. These results illustrate the power of action spectroscopy, not only in measuring the absorption bands of isolated ions, but also in studying the dynamics and thermodynamics of these intriguing systems. 

 

Dr. Yael Roichman, Department of Chemistry, Tel Aviv University
13/03/2013 - 12:00 - 13:00

Computer generated holograms afford an interactive and flexible way to modify light beams. In this talk I will describe two different applications of computer generated holograms; holographic optical tweezers, and parallel super resolution STED imaging.
In both applications holograms are created by a spatial light modulator and are used both to shape the beam, align the beam and correct for aberrations. I will conclude with a study of non-equilibrium dynamics done by holographic optical tweezers.
 

Andrew Grier, Laboratoire Kastler Brossel, Ecole Normale Supérieure, Paris
21/02/2013 - 15:00 - 16:00

Magnetically-tunable Feshbach resonances allow one to change the atom-atom scattering properties in ultracold atomic gases to arbitrary strength and sign, subject only to limitations imposed by the finite temperature of the gas.  Studies of Fermi gases taken directly to the atom-atom scattering resonance have led, among other results, to experimental investigations of BCS-BEC crossover physics which provide direct tests of theories of superconductivity.  However, when bosonic gases are taken to the point of divergent scattering length, rapid three-body recombination limits the lifetime of the gas and can even break the criterion for maintaining thermal equilibrium throughout the ensemble of atoms.

 

In this talk, I will present recent experimental and theoretical work done at LKB/IFRAF in the group of Christophe Salomon on an ensemble of ultracold lithium-7 taken to a Feshbach scattering resonance.  I will present a measurement of the lifetime of the gas at and around this scattering resonance and provide a framework with which to understand the loss process based on the theoretical work done by our colleagues in the group.  I hope to provide some insight on how to think of three-body losses in the regime where the two-body interaction becomes arbitrarily large.

Dr. Tal Ellenbogen, Department of Physical Electronics, School of Electrical Engineering, Tel-Aviv University
13/02/2013 - 12:00 - 13:00

Recent years have seen enormous advancements in the precise fabrication capabilities of micro- and nano-sturctures which led to the emergence of the exciting field of nanophotonics. This is due to the fact that the optical properties of nanostructured materials can be engineered and the interaction between light and matter is strongly affected by encapsulating photons in such structures and materials.  

In my talk I will present some examples of light manipulation by exploiting strong interactions in micro- and nano-structures. I will show how a leaky planar optical waveguide doped with excitonic gain material acts as an optical antenna which radiates quasi-coherent cylindrical vector beams. I will then show that by increasing the oscillator strength of the excitonic material strong coupling between waveguide photons and excitons can be observed. This changes the dynamics of the coupled system and splits its eigenmodes into mixed photon-exciton modes which share properties of light and matter. Finally I will present the development of tunable plasmonic color filters based on the excitation of localized surface plasmons in unique optical nano-antennas and show some of their applications.

Nirit Dudovich, Dept. of Physics of Complex Systems, Weizmann Institute of Science
06/02/2013 - 12:00 - 13:00

The interaction of intense light with atoms or molecules can lead to the generation of extreme ultraviolet (XUV) pulses and energetic electron pulses of attosecond (10-18) duration. The advent of attosecond technology opens up new fields of time-resolved studies in which transient electronic dynamics can be studied with a temporal resolution that was previously unattainable.

I will review the main challenges and goals in the field of attosecond science. As an example, I will focus on a recent experiment where the dynamics of tunnel ionization – one of the most fundamental strong-field phenomena – were studied. Specifically, we were able to measure the times when different electron trajectories exit from under the tunneling barrier created by a laser field and the atomic binding potential. In the following stage, subtle delays in ionization times from two orbitals in a molecular system were resolved. This experiment provides an additional, important step towards achieving the ability to resolve multielectron phenomena -- a long-term goal of attosecond studies.

Prof. David Sarkisyan, Institute for Physical Research, Armenian Academy of Sciences, 0203 Ashtarak, Armenia
06/02/2013 - 12:00 - 13:00

 

The results of the peculiarities of the electromagnetically induced transparency (EIT) resonance formation when the atomic vapor column is vary in the range of 100 nm up to 1 mm will be presented. Particularly, use of  30-μm-thin cell filled with the Rb and neon gas allows us  to reveal that the  Rb atoms enter the hyperfine Paschen–Back regime in magnetic fields of >1500 G .

            The results on the N –type resonances excited in the Rb atoms confined in a thin cells with variable thickness from 1 μm to 1 mm for the cases of a pure Rb atomic vapor and of a vapor with neon gas admission will be presented. Good contrast and narrow linewidth obtained in 40-μm-thin cell was exploited to study the splitting of the N-type resonance in a magnetic field of up to 2200 G .

Comparison between the EIT- and N-type resonances will be presented.

 

Nir Kampel, QUANTOP - Danish Center for Quantum Optics at the Niels Bohr Institute, Copenhagen University
30/01/2013 - 12:00 - 13:00
Recently a surprising experimental result has showed that Rayleigh superradiance is detuning asymmetric [1]. The theory trying to explain the asymmetry [1,2] has been the source of a debate [3] about the actual origin of the asymmetry. Here we present our experimental data and an alternative explanation for the phenomenon [4].
By measuring the onset of Rayleigh superradiance, we get a sensitive monitor of the matter-wave coherence. We model the loss of coherence as an additional detuning dependent loss term in a rate equation type of model, typically used to describe Rayleigh superradiance. The additional loss term originates from the light assisted collisions followed by radiation trapping. We compare the experimental results to the model and find reasonable agreement.

[1] L. Deng, et al., PRL, 105, 20404 (2010).
[2] L. Deng, et al., PRL, 104, 050402 (2010).
[3]  W. Ketterle, PRL, 106, 118901 (2011); L. Deng, et al., PRL, 106, 118902
(2011).
[4]  N. S. Kampel, et at., PRL, 108, 090401 (2012).
Dr. Sharly Fleischer, MIT
27/01/2013 - 12:00 - 13:00

Fundamental aspects and spectroscopic applications of resonantly driven molecular rotation

 

Recent advents of intense terahertz field generation have paved the way for nonlinear spectroscopy and coherent control in this unique region of the electromagnetic spectrum. Sub-picosecond terahertz fields resonantly interact with many rotational states simultaneously, and result in repetitive molecular orientation. I will present the fundamental aspects of terahertz induced molecular rotations and its spectroscopic applications, and focus on our recent observation of non-continuous decay profiles of excited rotational populations – a general phenomenon that is revealed in a uniquely pictorial way in a multilevel rotational system.

Dr. Dan Marom, Dept. of Applied Physics, Hebrew University in Jerusalem
16/01/2013 - 12:30 - 13:30

Time-to-space conversion of ultrafast optical waveforms is one of the less-common techniques employed for the detection of high bit rate optical communications. Although the technique has many virtues, as will be discussed, it is encumbered by a rather complex free-space optical arrangement and low conversion efficiency.

In this talk I will present our recent work on the development of the time-to-space converter, addressing these limitations. These developments lead to our long term goal of realizing the processor in a guided-wave platform. This will enable the processor to become a viable technology, applicable to many ultrafast measurement fields.

Prof. Aharon J. Agranat, The Hebrew University in Jerusalem
09/01/2013 - 12:00 - 13:00

Potassium tantalate niobate (KTN) is an oxygen perovskite crystal which at the paraelectric (PE) phase exhibits an exceptionally strong quadratic electrooptical (EO) effect. At temperatures slightly above the ferroelectric (FE) phase transition temperature Tc, KTN manifests an electrically induced change in the refractive index of »10-2. And yet, this exceptionally strong EO effect has hardly been exploited for applications.

This is partly because of scattering that occur in the vicinity of Tc. Investigations of these scattering phenomena reveal that the EO effect in this region is governed by the interplay between the classical deterministic "crystal optics" mechanism, and the stochastic formation of dipolar clusters that occur in the vicinity of Tc, fluctuating in space and time.

It will be shown how these scattering phenomena affect the EO behavior of KTN, and how they can be inhibited in potassium lithium tantalate niobate (KLTN). It will also be shown how KLTN can be operated at visible wavelengths without developing optical damage due to the formation of random space charge.

The photorefractive (PR) effect at the paraelectric phase in the vicinity of Tc will then be discussed, and its use for electroholography will be shown. Electroholographic diffraction with wide range electric tunability of the Bragg condition will be demonstrated. Emloying this phenomenon for the implementation of a laser with electric tunability through the entire C band.

The effect of the dipolar clusters on beam propagation in photorefractive KLTN will then be discussed, in particular, diffractionless propagation in minute reduced refractive index tunnels formed by fast quenching of the dipolar clusters to freeze spatial solitons.

Finally, a generic fabrication technique of 3D structures with sub-wavelength dimensions and reduced refractive index based on the implementation of fast ions in a KLTN substrate will be presented, and its potential for the construction of complex EO integrated circuits in which multitudes of EO devices and photonic structures are interconnected by a mesh of waveguides and operate in unison.

Dr. Sharon Shwartz, Bar Ilan University
02/01/2013 - 12:00 - 13:00

X-ray free-electron lasers operating in the angstrom regime have recently become available. These new systems, which deliver femtosecond-scale pulses with peak intensity exceeding 1018 W/cm2, open the path to new experiments in the field of nonlinear optics at x-ray wavelengths. Recently, we have observed phase-matched x-ray second harmonic generation of a pump beam at 1.7 Å. I will describe the experiment, and the theory of second order nonlinearity at x-ray wavelengths. I will discuss future directions, including the possibility of using second harmonic generation as a temporal correlator for diagnostics of ultrafast phenomena in the x-ray regime.

Yossi Paltiel, Applied Physics Department, Center for nano science and nano technology Hebrew University, Givat Ram, Jerusalem 91904, Israel, paltiel@cc.huji.ac.il
26/12/2012 - 12:00 - 13:00

Quantum nano- optics devices are likely to become primary components of future electronic devices. Practical realization of quantum devices faces a number of challenges. However, the benefits from the successful implementation of these devices can be enormous. Nature in several cases uses quantum mechanics in order to achieve extraordinary properties. One known examples is the high photon conversion efficiency in photosynthetic light harvesting complexes. In this example the most striking feature is the use of coherence properties and quantum mechanics in the short scale while the measurements and results are classical in the large scale. In my lab we aim to mimic nature and create nano tool box bottom up approach which enables high temperature quantum operation coupled to top down classical semiconductor measurement device (See [1] for example).

This methodology is producing a generic technology for constructing nano-systems in which many devices are interconnected and operate in unison, without inhibiting their quantum nature. In the talk we will present our efforts to achieve confinement potential control using different dots systems [2,3] as well as charge and spin transfer control in our hybrid dots systems [4]. We will show our recent results in which we were able to discover a collective electron transfer process by studying the current noise in a field effect transistor with light-sensitive gate formed by nanocrystals linked by organic molecules to its surface [5]. A demonstration of a room temperature operating hybrid quantum sensor will be presented, together with antennas for enhancing the efficiency of solar cells.

 We hope that by controlling the quantum and classical behavior of the self assembled layers we will be able to create novel and revolutionary devices mimicking some of Nature's complex structures. One such example would be mimicking the light harvesting complexes in a controlled self assembled design. Using the flexibility of the design we can realize systems which will test the some of the suggested quantum theories. Further into the future we aim to use this knowledge for applicable devices such as increasing the efficiency of solar cells coupled to simple Si based devices.

 

 

[1] N. Livneh et al. Nano Lett. 11, 1630 (2011).

[2] S. Shusterman et al. Europhys Letters 88 (2009) 66003.

[3] D. P. Kumah et al. Nature Nanotechnology 4 (2009) 835.

[4] T. Aqua   et al. Appl. Phys. Lett. 92  (2008) 223112.

[5] Y. Paltiel et al.  Phys. Rev. Lett. 104, 016804 (2010).

Dr. Nir Bar-Gil, Harvard University
19/12/2012 - 12:00 - 13:00
Nitrogen-Vacancy (NV) color centers in diamond provide an atomic-like quantum system embedded in a solid-state structure. As such, they offer a bridge between the fields of atomic physics and condensed matter physics, with emerging applications ranging from quantum many-body spin dynamics to quantum information processing and magnetic field sensing.
In this talk I will introduce the field of NV centers, and describe our research into understanding and controlling these systems, with the future goal of studying controllable many-body quantum spin systems. I will first present our realization of a coherent spectroscopic technique, in which the NV is used as a probe of the dynamics of its composite solid-state spin environment. Using this technique, we identify a possible new mechanism in diamond for suppression of electronic spin bath dynamics in the presence of a nuclear spin bath of sufficient concentration.
I will then describe our work on applying dynamical decoupling approaches to extend the limit of the coherence time of the NV spin qubit, achieving record coherence times for solid-state electronic spins. I will further mention experiments in which In addition to controlling the NVs, we directly drive the surrounding bath spins and observe the transfer of polarization from the NVs to the bath, paving the way for spin bath cooling.
I will conclude by discussing ways to engineer NV-based quantum spin simulators based on these results, and answer outstanding questions in many-body dynamics, topological phases and beyond.
 

 

Shahar Levy, Faculty of Engineering, Bar-Ilan University, Ramat-Gan 52900 Israel
12/12/2012 - 12:00 - 13:00

Stimulated Brillouin scattering (SBS) is a nonlinear interaction between a relatively intense pump wave, and a counter-propagating, spectrally detuned probe wave. When the difference between the optical frequencies of the two waves matches the Brillouin frequency shift of the medium WB, the probe wave may be amplified at the expense of the pump. SBS is readily observed in standard silica single-mode fibers over lengths of hundreds of meters.

Chalcogenides (ChGs) are a family of glasses which contain one of the chalcogen elements (e.g. S, Se, or Te). They have a broad transparency window from the visible to the mid-infrared wavelengths, and are well known for their highly-nonlinear refractive index n2, that is up to thousand times greater than that of silica. The large nonlinearity makes ChGs an attractive platform for all-optical signal processing. Nonlinear propagation effects in waveguides written in ChG glass have been used in four-wave-mixing, in wavelength conversion etc.

Recently, SBS amplification was demonstrated in 7 cm-long As2S3 waveguides, defined using a dry-etch process. In this work, we report SBS amplification in As2S3 waveguides defined by a much simpler technique of direct laser-beam writing. 1 cm-long and 4 mm-wide waveguides were patterned in a 1 mm-thick film of As2S3, deposited on a silica-on-silicon substrate. The results provide the first demonstration of SBS amplification in directly-written chalcogenide glass waveguides. The observed gain bandwidth of 200 MHz is considerably wider than previously reported values of ~30MHz. A possible explanation due to multi-mode behavior along with the longitudal evolution of the optical field profile will be discussed.

Dr. Revital Shechter, President, VP of R&D and Co-Founder of Ornim medical
28/11/2012 - 12:00 - 13:00

Monitoring Tissue Blood Flow is vital during states of decreased or increased flow. However, there are currently no non-invasive devices that measure microcirculatory blood flow in tissue continuously. This talk will present a novel device that uses Ultrasound Modulation of Diffused Light to perform non-invasive monitoring of blood flow at the microcirculatory level underneath its sensor.

We demonstrate the ability of Ornim's device ( the CerOx) to monitor tissue blood flow in various situations. The ability to monitor critical processes such as autoregulation in the brain and its clinical importance are shown.

Dr. Avi Pe'er, BIU
21/11/2012 - 12:00 - 13:00

Measurement of vibrational dynamics in molecules is key to the understanding of chemical processes, such as the evolution of chemical reactions, and to the ability to control them. Current methods, such as molecular tomography or pump-probe techniques generally suffer from a very low signal per molecule (1 photon or less), limiting their sensitivity and applicability. I will describe a method to coherently amplify the signal per molecule using a coherent Raman oscillator that is synchronously pumped by an optical frequency comb, thereby improving the sensitivity of detection by orders of magnitude.

By placing the molecules in an optical cavity that is synchronously pumped by a frequency comb laser source, the emission from the molecular excitation of one pulse returns to the molecule in phase with subsequent excitations and can be amplified by stimulated emission. The cavity can therefore serve as a memory that maintains the coherent emission between the pulses, enabling amplification by stimulation of the emitted signal per molecule. As we have recently shown in extensive simulation and calculation, this coherent amplifier can easily cross the oscillation threshold, producing short bursts of strong optical pulses that directly represent the wave-packet dynamics initiated by the pump pulses in the excited electronic potential.

Such an oscillator will improve the signal to noise ratio of measurements by several orders of magnitude compared to standard techniques and may open avenues for analysis of chemical reactions in the femtosecond time scale. Since here, the cavity serves as the coherent memory and not the molecules themselves, the scheme operates well also when the molecular coherence times are short; i.e. with molecules in hot / room temperature conditions, and also in solution / on surface, which broadens the scope of applicability significantly.

I will describe our (so far theoretical) research of this unique Raman oscillator , its fascinating coherence properties and the experiments we plan to perform with it.

Daniel Kravitz, Faculty of Engineering, Bar-Ilan University
14/11/2012 - 12:00 - 13:00

Abstract:  High resolution ranging systems are of great importance for both civilian and military applications. Both radio frequency (RF) waveforms and optical waveforms (LADAR) are used for range detection purposes. In both techniques, high range resolution can be obtained using short and intense pulses. However, the transmission and processing of such pulses is difficult and potentially unsafe. Instead, temporally extended waveforms or sequences, in conjunction with proper compression techniques at the receiver end, may be used. The instantaneous power of the extended waveforms can be orders-of-magnitude lower, making them safer and simpler to generate in a real-world system and more difficult to intercept by an adversary.

In this work, I propose and demonstrate two distinct schemes for high resolution ranging measurements. The first proposition is a microwave-photonic, ultra-wideband (UWB) noise RADAR system. The system makes use of the amplified spontaneous emission (ASE) of optical amplifiers to generate random 'physical noise' that is later converted to the RF domain. The system comprised of a central unit and remote end unit that were separated by 10 km of fiber. A range resolution of 10 cm was achieved using this system.

The second technique is a LADAR system, employing an encoded sequence of pulses and a proper post-processing to obtain high resolution ranging measurements with low sidelobes. A novel compression scheme, previously proposed by Prof. Nadav Levanon of Tel-Aviv Univ., was employed in the experiment. The method achieved the sidelobe suppression of complex coherent receivers, even though a simple direct detector was employed. A ranging resolution of 3 cm was obtained.