Phase-sensitive Quantum CARS beyond the classical limit

QUEST Center event
Yes
Speaker
Yoad Michael, Bar Ilan
Date
24/05/2017 - 16:00 - 15:00Add to Calendar 2017-05-24 15:00:00 2017-05-24 16:00:00 Phase-sensitive Quantum CARS beyond the classical limit 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.  Nanotechnology center, 9th floor seminar room המחלקה לפיזיקה physics.dept@mail.biu.ac.il Asia/Jerusalem public
Place
Nanotechnology center, 9th floor seminar room
Abstract

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. 

תאריך עדכון אחרון : 21/05/2017