Towards a tunable graphene-based Landau level laser in the terahertz regime.

Florian Wendler,Ermin Malic

doi:10.1038/srep12646

Abstract

Terahertz (THz) technology has attracted enormous interest with conceivable applications ranging from basic science to advanced technology. One of the main challenges remains the realization of a well controlled and easily tunable THz source. Here, we predict the occurrence of a long-lived population inversion in Landau-quantized graphene (i.e. graphene in an external magnetic field) suggesting the design of tunable THz Landau level lasers. The unconventional non-equidistant quantization in graphene offers optimal conditions to overcome the counteracting Coulomb- and phonon-assisted scattering channels. In addition to the tunability of the laser frequency, we show that also the polarization of the emitted light can be controlled. Based on our microscopic insights into the underlying many-particle mechanisms, we propose two different experimentally realizable schemes to design tunable graphene-based THz Landau level lasers.

Highlights

We present two different experimentally feasible mechanisms to achieve the population inversion induced by optical pumping, cf
While the carrier dynamics without a magnetic field has been already thoroughly studied in experiment[17,21,22,23,24] and theory[14,24,25,26,27,28,29], its investigation in Landau-quantized graphene has just started to pick up pace very recently[19,30,31,32]
We have developed a theory based on the density matrix approach[29] providing access to time and energy-dependent relaxation dynamics in Landau-quantized graphene and revealing microscopic insights into the underlying many-particle scattering pathways[30,31]

Summary

Introduction

The first mechanism (A) is based on the specific optical selection rules in Landau-quantized graphene yielding the possibility to selectively pump a single LL transition constituting an effectively three-level laser system, cf Fig. 1A. Using a linearly polarized optical excitation field with an energy matching the inter-Landau level transition LL−3 → LL+2 (and LL−2 → LL+3), a population inversion between LL+1 and LL+2 (σ+-PI) (and between and between LL−2 and LL−1 (σ−-PI)) is generated.

Results

Conclusion