The role of intraband dynamics in the generation of circularly polarized high harmonics from solids

TL;DR

This paper investigates how intraband electron dynamics influence the polarization of high harmonics generated in solids, revealing mechanisms for controlling harmonic polarization states and distinguishing generation processes.

Contribution

It introduces a method combining intraband calculations and experiments to analyze polarization effects in high-harmonic generation from solids.

Findings

Intraband dynamics can produce circularly polarized harmonics from elliptical pulses.

Depolarization effects occur at higher field strengths due to intraband processes.

Interband dynamics dominate for harmonics above the band gap, affecting polarization.

Abstract

Recent studies have demonstrated that the polarization states of high harmonics from solids can differ from those of the driving pulses. To gain insights on the microscopic origin of this behavior, we perform one-particle intraband-only calculations and reproduce some of the most striking observations. For instance, our calculations yield circularly polarized harmonics from elliptically polarized pulses that sensitively depend on the driving conditions. Furthermore, we perform experiments on ZnS and find partly similar characteristics as reported from silicon. Comparison to our intraband-only calculations shows reasonable qualitative agreement for a below-band-gap harmonic. We show that intraband dynamics predict depolarization effects for higher field strengths. For harmonics above the band gap, interband dynamics become important and the high-harmonic response to elliptical excitation looks systematically different. Our work proposes a method to distinguish between different high-harmonic generation mechanisms and it could pave the way to compact solid-state high-harmonic sources with controllable polarization states.