Beyond the effective mass approximation: predictive theory of the nonlinear optical response of conduction electrons

TL;DR

This paper develops a predictive semiclassical model for the nonlinear optical response of conduction electrons in semiconductors under intense THz fields, surpassing the limitations of the effective mass approximation.

Contribution

It introduces a comprehensive theoretical framework combining realistic band structure and Drude parameters to accurately predict nonlinear optical phenomena in conduction electrons.

Findings

Experimental validation of saturable absorption and refractive index changes

Model accurately reproduces experimental nonlinear responses in InSb

Path established for predictive modeling in THz plasmonics and metamaterials

Abstract

We present an experimental and computational study of the nonlinear optical response of conduction electrons to intense terahertz (THz) electric field. Our observations (saturable absorption and an amplitude-dependent group refractive index) can be understood on the qualitative level as the breakdown of the effective mass approximation. However, a predictive theoretical description of the nonlinearity has been missing. We propose a model based on the semiclassical electron dynamics, a realistic band structure, and the free electron Drude parameters to accurately calculate the experimental observables in InSb. Our results open a path to predictive modeling of the conduction-electron optical nonlinearity in semiconductors, metamaterials, as well as high-field effects in THz plasmonics.