How a ridge polariton laser is different from a standard ridge laser

The physics of gain in interband semiconductor lasers is mostly discussed in terms of population inversion for electrons and holes and the associated Bernard-Durrafourg condition. Due to the reciprocity between the processes of absorption and stimulated emission, one consequence is that lasing action can only be reached in standard ridge lasers if the pumped section of a laser is longer than the unpumped (absorptive) section. Here we present how a polariton laser, in a ridge waveguide laser geometry very similar to that of standard ridge lasers, operates on a fundamentally different lasing scheme. Alike multi-section lasers, this laser can be optically pumped over an adjustable length, and we show that lasing action is observed for a pumped length equal to only 15% of the cavity. Based on this striking feature, the comparison between polariton gain and population inversion will be didactically discussed.