The ultrafast path of circularly polarized high-order harmonics: from the first demonstrations to photon-hungry applications
QUEST Center event:
Dr. Ofer Kfir, University of Göttingen
26/06/2019 - 12:00 - 13:00
Nano Center, 9th floor seminar room
Generation of high harmonics of light fields had led to numerous scientific and technological advancements since its discovery 30 years ago, including attosecond spectroscopy of atoms, molecules and condensed matter and table-top high-resolution imaging of nanostructures. However, the polarization state of high harmonics was essentially limited to linear, which prevented experimental access to the role of photon-spin in harmonic generation, and hindered the use of high harmonic radiation for chiro-optical investigation with magnetic and other chiral matter.
My talk will follow the path that circularly polarized high harmonics followed in the past few years, from their inexistence, through the first demonstrations [1,2], and the current state of the art . In the first part, I describe the dynamical symmetries that impose polarization constraints on the interaction of light and matter, both at the level of a single atom and of an ensemble. The second part focuses on application of high harmonics for lensless magnetic-imaging, which is especially demanding in terms of the photon-flux and polarization control – two traditional challenges of HHG. I will show quantitative mapping of magnetic domains, which surpass results from large facilities (e.g. synchrotrons) in both space and time: Spatially, by reaching image resolution below the wavelength on a large field-of-view, and temporally, by observing 200 femtosecond dynamics of the magnetic patterns. In the future, accessibility to a new spatio-temporal scales may reveal new dynamical phenomena, and allow for a better understanding of ultrafast magnetism.
 A. Fleischer, O. Kfir, et. al., Nat. Photonics 8, 543 (2014).
 O. Kfir, et. al., Nat. Photonics 9, 99 (2015).
 O. Kfir, et. al., Sci. Adv. 3, eaao4641 (2017).