Theoretical backgrounds of nonlinear THz spectroscopy of semiconductor superlattices

TL;DR

This paper develops a theoretical framework for understanding terahertz absorption and gain in semiconductor superlattices under bichromatic electric fields, highlighting parametric and incoherent interactions without requiring negative differential conductivity.

Contribution

It provides an exact solution to the Boltzmann transport equation for this system, elucidating the mechanisms of THz gain control in superlattices.

Findings

Formulas include parametric and incoherent interaction terms.

THz gain can be controlled without negative differential conductivity.

Theoretical background for THz spectroscopy in superlattices.

Abstract

We consider terahertz absorption and gain in a single miniband of semiconductor superlattice subject to a bichromatic electric field in the most general case of commensurate frequencies of the probe and pump fields. Using an exact solution of Boltzmann transport equation, we show that in the small-signal limit the formulas for absorption always contain two distinct terms related to the parametric and incoherent interactions of miniband electrons with the alternating pump field. It provides a theoretical background for a control of THz gain without switching to the negative differential conductivity state. For pedagogical reasons we present derivations of formulas in detail.