Propagation-induced limits to high harmonic generation in 3D Dirac semimetals

TL;DR

This paper investigates how propagation effects in 3D Dirac semimetals influence high harmonic generation, revealing an optimal film thickness for maximum HHG efficiency due to propagation-induced dephasing.

Contribution

It demonstrates the fundamental role of propagation dynamics in limiting HHG enhancement in 3D DSM nanofilms, a novel insight into nonlinear optical processes in these materials.

Findings

Orders-of-magnitude increase in HHG with thicker films

Existence of an optimal film thickness for maximum HHG

Propagation-induced dephasing limits HHG beyond optimal thickness

Abstract

3D Dirac semimetals (DSMs) are promising materials for terahertz high harmonic generation (HHG). We show that 3D DSMs' high nonlinearity opens up a regime of nonlinear optics where extreme subwavelength current density features develop within nanoscale propagation distances of the driving field. Our results reveal orders-of-magnitude enhancement in HHG intensity with thicker 3D DSM films, and show that these subwavelength features fundamentally limit HHG enhancement beyond an optimal film thickness. This decrease in HHG intensity beyond the optimal thickness constitutes an effective propagation-induced dephasing. Our findings highlight the importance of propagation dynamics in nanofilms of extreme optical nonlinearity.