Lasing threshold doubling at the crossover from strong to weak coupling regime in GaAs microcavity

In a polariton, laser coherent monochromatic light is produced by a low-energy state of the system at the bottom of a polariton 'trap', where a condensate of polaritons is formed, requiring no conventional population inversion. Following the recent realization of polariton light-emitting diodes (LEDs) based on GaAs microcavities (MCs) operating up to room temperature, efforts have been directed towards the demonstration of an electrically injected polariton laser. However, until now, low-threshold polariton lasing in GaAs MCs under optical pumping has been reported only at low temperatures. Here, we investigate the temperature dependence of lasing threshold across the border of the strong-to-weak coupling regime transition in high-finesse GaAs MCs under non-resonant optical pumping. Remarkably, we find that although lasing in the strong coupling regime is lost when the temperature is raised from 25 to 70 K, the threshold only doubles, in stark contrast with the expected difference of two orders of magnitude. Our results can be explained by considering temperature-induced thermalization of carriers to high wavevector states, increasing the reservoir's overall carrier lifetime, resulting in an order of magnitude higher steady-state carrier density at 70 K under similar pumping conditions.