Crystal orientation-dependent polarization state of high-order harmonics

TL;DR

This study investigates how the polarization of high-order harmonics generated in magnesium oxide crystals depends on crystal orientation, revealing deviations from laser polarization influenced by crystal symmetry, harmonic order, and laser intensity.

Contribution

It introduces a real-space electron trajectory model to analyze the polarization state of high-order harmonics based on crystal orientation, advancing understanding of electron dynamics in strong fields.

Findings

High-symmetry directions produce harmonics with polarization aligned to the laser.

Polarization deviation depends on crystal orientation, harmonic order, and laser strength.

Results enable all-optical probing of atomic and electronic structures.

Abstract

We analyze the crystal orientation-dependent polarization state of extreme ultraviolet (XUV) high-order harmonics from bulk magnesium oxide crystals subjected to intense linearly polarized laser fields. We find that only along high-symmetry directions in crystals high-order harmonics follow the polarization direction of the laser field. In general, the polarization direction of high-order harmonics deviates from that of the laser field, and the deviation amplitude depends on the crystal orientation, harmonic order and the strength of the laser field. We use a real-space electron trajectory model to understand the crystal orientation-dependent polarization state of XUV harmonics. The polarization analysis allows us to track the motion of strong-field-driven electron in conduction bands in two dimensions. These results have implications in all-optical probing of atomic-scale structure in real-space, electronic band-structure in momentum space, and in the possibility of generating attosecond pulses with time-dependent polarization in a compact setup.