Coherent quasimodes and supermodes in a planar microcavity

A homogeneous microcavity is excited in two tightly focused spatially separated spots with a few μm distance. The radius of the generated cavity modes exceeds the excited regions such that the quasimodes of both spots overlap in space. Coherent coupling of the two spots via stimulated emission is observed, exhibiting a slightly lowered lasing threshold. Furthermore, the emission from both spots is phase locked with a phase difference of either 0 or π , depending on their separation. Correspondingly, the distribution of the electromagnetic field is symmetric or anti-symmetric, and the emission occurs parallel to the cavity normal or symmetrically at non-zero angles, respectively. This behaviour is understood to be determined by the spatial distribution of gain and absorption across the active cavity medium, which we confirm by numerical calculations.