Effect of heating and cooling of photogenerated electron-hole plasma in optically pumped graphene on population inversion

TL;DR

This paper investigates how heating and cooling of photogenerated electron-hole plasma in optically pumped graphene affect population inversion and dynamic conductivity, with implications for room-temperature graphene-based terahertz and infrared lasers.

Contribution

It models the effects of electron-hole plasma heating, cooling, and nonequilibrium phonons on optical properties and conditions for negative dynamic conductivity in pumped graphene.

Findings

Dynamic conductivity can become negative at certain frequencies.

Electron-hole plasma temperature influences population inversion.

Conditions for achieving negative conductivity at room temperature are identified.

Abstract

We study the characteristics of photogenerated electron-hole plasma in optically pumped graphene layers at elevated (room) temperatures when the interband and intraband processes of emission and absorption of optical phonons play a crucial role. The electron-hole plasma heating and cooling as well as the effect of nonequilibrium optical phonons are taken into account. % The dependences of the quasi-Fermi energy and effective temperature of optically pumped graphene layers on the intensity of pumping radiation are calculated. The variation of the frequency dependences dynamic conductivity with increasing pumping intensity as well as the conditions when this conductivity becomes negative in a certain range of frequencies are considered. % The effects under consideration can markedly influence the achievement of the negative dynamic conductivity in optically pumped graphene layers associated with the population inversion and, hence, the realization graphene-based terahertz and infrared lasers operating at room temperatures.