Intersubband polariton-LO phonon interaction in mid-infrared non-dispersive cavities: experimental demonstration of spontaneous scattering and perspectives towards polariton lasing [Invited]

We report experimental evidence of the interaction between intersubband polaritons and longitudinal optical phonons in non-dispersive mid-infrared cavities, under resonant optical injection. Light emission originating from spontaneous polariton-phonon scattering is observed at a frequency corresponding to an energy shift of one phonon below the pump frequency. Given the extremely low spontaneous scattering rate, we employ a custom-developed quantum mechanical model to numerically demonstrate the feasibility of stimulating such a process using a pump–probe scheme. Based on this theoretical framework, we identify a set of experimental conditions under which optical gain may be realized in an intersubband polaritonic system.