Lasing emission from stable and unstable modes of deformed GaN microdisks

Summary form only given. We report data from GaN microdisk lasers at various deformations, where the lasing modes are also found to be based on distinct periodic ray orbits (PROs), but with varying stabilities. The quadrupolar-deformed laser (QD) at /spl epsiv/ = 0.12 is found to lase on unstable triangular PROs, which strike the boundary near the critical angle. In the case of the hexa-decapolar deformed laser (Q-HD), it is shown that one and the same PRO is responsible for lasing over a wide range of deformations, although it undergoes a stable-to-unstable transition in that range. Furthermore, we show that a naive application of Snell´s law to the ray orbit yields erroneous results for the far-field emission pattern. We find that there is an angular shift with respect to the expected far-field pattern based on ray tracing, which becomes maximum close to the critical angle.