Following Phonon Dynamics in Solids Using High-Harmonic Spectroscopy*

Ever since the first observation of high-order harmonic generation (HHG) from zinc-oxide [1], the field of HHG from solids has seen tremendous growth with many reports of HHG from a variety of materials as well as their applications in spectroscopy or potential industrial market [2-5]. HHG from solids has quickly formed a significant sub-field of attosecond science. In this work, we demonstrate the substantial power of high harmonic spectroscopy of solids in investigating carrier-phonon scattering in solids. Utilizing the non-collinear two-color interferometric measurements, we obtain unambiguous ultra-high-order wave mixing in solids, extending from the gas phase experiments [6]. Furthermore, by exercising control over the pump and probe laser pulses as well as their delay and polarization, we can initiate, control, and follow the phonon dynamics in real time with unprecedented capabilities. The experimental results are fully supported by theoretical simulations using different methodologies (two-level model including phenomenological phonon coupling, semi-conductor band model including carrier-phonon interaction). Being coupled with theoretical simulations, our experimental results would help in characterizing the carrier-phonon coupling strength, phonon creation and relaxation, and multiple-phonon dynamics in a solid system. We anticipate our work would help reveal carrier-phonon scattering in a brand-new dimension, extracting in-depth information.