Laser emission with hybrid resonant mode from an active peanut-shaped microcavity

Two basic types of resonances exist in microcavities. One is whispering gallery mode (WGM) resonance which occurs particularly in circular and elliptical-shaped micro-disks. The other type of resonance is multiple-bouncing periodic orbit. Bow-tie bouncing modes found in a quadruple-shaped cavity and some types of scar modes in chaotic systems are typical examples. Emission directionality from a microcavity is an important property because achieving highly collimated emission (comparable to that of a bulk laser system) from microcavity lasers is essential to obtain high brightness micro-light sources for coupling with other optical systems. Asymmetric resonant cavities (ABCs) have been designed and fabricated to achieve laser emissions with directionality, however, the beam divergences of all those reported ABCs were found to be of ten degrees at least. In this work, we report an observation of directional laser emission with extremely narrow divergence (about 2deg) from a peanut-shaped microcavity. This narrow divergence is very promising for the microcavity to be used as micro-lasers with high brightness. We also demonstrated that the real resonance in a peanut-shaped microcavity is a very special hybrid resonance which combines a whispering gallery orbit and a two-bouncing orbit.