Spectral caustics of high-order harmonics in one-dimensional periodic crystals

TL;DR

This paper explores the spectral caustics in high-order harmonic generation in 1D solids, revealing new catastrophe singularities and demonstrating control via two-color laser fields, enhancing understanding and manipulation of HHG spectra.

Contribution

It introduces a new type of catastrophe singularity in HHG spectra of solids and demonstrates control of these singularities using two-color laser fields.

Findings

Identification of new catastrophe singularities in HHG spectra.

Agreement between diffraction patterns and semi-classical electron-hole trajectories.

Control of spectral caustics through laser field parameters.

Abstract

We theoretically investigate the spectral caustics of high-order harmonics in solids. We analyze the 1-dimension model of solids HHG and find that, apart from the caustics originated from the van Hove singularities in the energy-band structure, another kind of catastrophe singularities also emerge when the different branches of electron-hole trajectories generating high-order harmonics coalesce into a single branch. We solve time-dependent Schr\"odinger equation in periodic potential and demonstrate the control of this kind of singularities in HHG with the aids of two-color laser fields. The diffraction patterns of the harmonic spectrum near the caustics agree well with the inter-band electron-hole recombination trajectories predicted by the semiconductor semi-classical equation. This work is expected to help to understand the HHG dynamics in solids and manipulate the harmonic spectrum by adjusting driving field parameters.