GTIIT-STU Optics Seminar

Title: Chiral broadband High Harmonic Generation Source by Triple-Symmetry-Breaking

Speaker: Dr. Avner Fleischer 

Department of Chemical Physics, School of Chemistry, Tel Aviv University

Abstract

Chiral XUV sources are pivotal for investigating chiroptical phenomena on the ultrafast electronic timescale. Table-top, coherent HHG-based sources are particularly well-suited for these studies. However, chiral materials, such as chiral organic molecules and solid-state magnetic materials, exhibit fine spectral features which necessitate broadband radiation [1] for their complete interrogation. The generation of HHG radiation which is both broadband and helical presents a seemingly paradoxical challenge: while chiral HHG emission requires at least two recollisions occurring along different directions in the polarization plane, as few as even three recollisions might already lead to the Floquet limit, resulting in a sparse spectrum characterized by pronounced discrete harmonic peaks. In the talk I will present a straightforward scheme that overcomes this challange, which is based on triple-symmetry-breaking of the most common HHG configuration (namely HHG driven by linearly-polarized monochromatic-like driver, in which a sparse spectrum of linearly-polarized odd-integer harmonics is obtained). First, by turning the single-color scheme into a two-color one, the sparse peaks broaden, due to the reduction of the number of recollisions. Second, turning the two-color scheme from scalar to vectorial (by making the two-colors cross-linearly-polarized) transforms the XUV radiation polarization state from linear to chiral. Lastly, adding ellipticity to both colors (by making the two-colors cross-elliptically-polarized) offers tunability over the spectral chirality. The scheme integrates the time-gating and polarization-gating techniques to generate a vectorial driver which induces well-controlled bursts of recollisions, occurring along different directions in the polarization plane. The broadband XUV radiation [2] exhibits rapid modulations in its spectral ellipticity, and fast alternation in its spectral helicities. We anticipate that our scheme will facilitate studies of high-resolution chiroptical phenomena is solids and chiral molecules, with the advantage of superior sensitivity and specificity.