Pulsed high harmonic generation of light due to pumped Bloch oscillations in noninteracting metals

TL;DR

This paper presents a simple theoretical model explaining high-order harmonic generation in noninteracting metals under strong oscillating electric fields, focusing on electron acceleration and current dynamics.

Contribution

It introduces a new model for high harmonic generation in metals that accounts for electron acceleration without considering interband transitions.

Findings

Odd harmonic frequencies can dominate the spectrum under certain conditions.

The model successfully applies to real materials like ZnO, matching experimental observations.

High harmonic generation is driven by electron acceleration due to the pump field.

Abstract

We derive a simple theory for high-order harmonic generation due to pumping a noninteracting metal with a large amplitude oscillating electric field. The model assumes that the radiated light field arises from the acceleration of electrons due to the time-varying current generated by the pump, and also assumes that the system has a constant density of photoexcited carriers, hence it ignores the dipole excitation between bands (which would create carriers in semiconductors). We examine the circumstances under which odd harmonic frequencies would be expected to dominate the spectrum of radiated light, and we also apply the model to real materials like ZnO, for which high-order harmonic generation has already been demonstrated in experiments.