Post-transient relaxation in graphene after an intense laser pulse

Abstract

High intensity laser pulses were recently shown to induce a population inverted transient state in graphene [T. Li et al. Phys. Rev. Lett. 108, 167401 (2012)]. Using a combination of hydrodynamic arguments and a kinetic theory we determine the post-transient state relaxation of hot, dense, population inverted electrons towards equilibrium. The cooling rate and charge-imbalance relaxation rate are determined from the Boltzmann-equation including electron-phonon scattering.We show that the relaxation of the population inversion, driven by inter-band scattering processes, is much slower than the relaxation of the electron temperature, which is determined by intra-band scattering processes. This insight may be of relevance for the application of graphene as an optical gain medium. 1 arXiv:1303.7014v1 [cond-mat.mes-hall]

Room temperature broadband terahertz gains in graphene heterostructures based on inter-layer radiative transitions

“…12,13 In particular, as a critical step towards graphene terahertz lasers, the possibilities of terahertz wave amplifications by graphene have attracted increasing research interest. Non-equilibrium carrier behaviors in optical pumped graphene have been studied theoretically and experimentally, [14][15][16][17][18][19][20][21] which showed population inversion in graphene is possible, and several graphene based terahertz laser concepts have also been proposed. [22][23][24][25] However, due to the ultrafast carrier relaxation dynamics, population inversion in graphene lasts for only a short time, 26,27 signifying a monolayer graphene may be not ideal for a terahertz laser gain material.…”