Selective excitation of different modes in noncircular GaN microdisk lasers

Summary form only given. Circular microdisk semiconductor lasers have low laser thresholds and outputs, because whispering gallery modes, which have high Q and Low non-directional output, provide their feedback. Stadium-shaped microdisk quantum-cascade lasers have greatly increased emission and directionality, because feedback is provided by the regular-orbit "bow-tie" modes. Despite high dislocation densities in GaN, we have achieved directional laser emission from quadrupolar-deformed GaN microdisks which have the same threshold as circular microdisks. With uniform optical pumping of the top face of the quadrupolar-shaped microdisk, the strongest directional emission emerges from the sidewall as four beams at 50/spl deg/ relative to the long axis. The feedback is attributed to chaotic-orbit modes that leak out by refraction, when rays have incident angle less than the critical angle.