Exciton-Population Inversion and Terahertz Gain in Resonantly Excited Semiconductors

TL;DR

This paper investigates how resonant laser excitation in semiconductors can create exciton population inversion, leading to terahertz gain, by converting polarization into incoherent exciton populations.

Contribution

It demonstrates the microscopic mechanism of exciton population inversion and terahertz gain in resonantly excited semiconductors, highlighting the conversion from polarization to incoherent exciton populations.

Findings

Inversion between 2p and 1s exciton states is achievable.

Polarization with s-type symmetry converts into incoherent p-type populations.

Significant terahertz gain is observed due to exciton population inversion.

Abstract

The build-up of exciton populations in resonantly laser excited semiconductors is studied microscopically. For excitation at the $2s$-exciton resonance, it is shown that polarization with a strict $s$-type radial symmetry can be efficiently converted into an incoherent $p$-type population. As a consequence, inversion between the $2p$ and $1s$ exciton states can be obtained leading to the appearance of significant terahertz gain.