Mode selection in GaAs micropillar polariton lasers

Semiconductor micropillars offer an interesting way of studying polaritons in zero-dimensional cavities. In such cavities, photons are confined vertically, by the Bragg mirrors, and laterally by the index of refraction contrast between the air and the semiconductor. Zero dimensional polariton modes are the result of this three-dimensional confinement. The first observation of polariton lasing in a GaAs micropillar showed single mode operation, with lasing from the lowest energy mode in the system. We demonstrate that by careful engineering of the system, competing relaxation mechanisms can be used to achieve lasing from higher energy modes.