Polarisation control of optically pumped terahertz lasers

Optical pumping of excited exciton states in semiconductor quantum wells is a tool for realisation of ultra-compact terahertz (THz) lasers based on stimulated optical transition between excited (2p) and ground (1s) exciton state. We show that the probability of two-photon absorption by a 2p-exciton is strongly dependent on the polarisation of both photons. Variation of the threshold power for THz lasing by a factor of 5 is predicted by switching from linear to circular pumping. We calculate the polarisation dependence of the THz emission and identify photon polarisation configurations for achieving maximum THz photon generation quantum efficiency.