# Ellipticity dependence of high-harmonic generation in solids: unraveling the interplay between intraband and interband dynamics

## TL;DR

This paper investigates how ellipticity of the driving laser influences high-harmonic generation in solids, revealing mechanisms to enhance harmonic cutoff and generate circularly polarized harmonics with controllable properties.

## Contribution

It provides a detailed first-principles analysis of intraband and interband effects under ellipticity, offering new methods to control HHG in solids.

## Key findings

- Ellipticity can increase the high-harmonic cutoff by up to 30%.
- Ellipticity enables generation of circularly polarized harmonics with alternating helicity.
- The interplay between intraband and interband effects is key to controlling HHG.

## Abstract

The strong ellipticity dependence of high-harmonic generation in gases enables numerous experimental techniques that are nowadays routinely used, for instance, to create isolated attosecond pulses. Extending such techniques to high-harmonic generation in solids requires a fundamental understanding of the microscopic mechanism of the high-harmonic generation. Here, using extensive first-principles simulations within a time-dependent density-functional framework, we show how intraband and interband mechanisms are strongly and differently affected by the ellipticity of the driving laser field. The complex interplay between intraband and interband effects can be used to tune and improve harmonic emission in solids. In particular, we show that the energy cutoff of the high-harmonic plateau can be increased by as much as 30\% using a finite ellipticity of the driving field, opening a new avenue for better understanding and control of HHG in solids based on ellipticity. Also, we demonstrate the possibility to generate, from a single circularly polarized driving field, circularly polarized harmonics with alternating helicity. Our work shows that ellipticity provides an additional knob to experimentally control high-order harmonic generation in solids.