Scarred mode lasing in quadrupole-shape microcavities

Deformed liquid-jet microcavity of low index of refraction has advantages of enabling continuous deformation of cavity, easy control of gain molecule concentration and highly smooth surface due to surface tension. These cavities have been shown to support scarred modes of cavity Q in the range of 10⁶ with directional emission consistent with an unstable periodic orbit that the scar modes correspond to. We demonstrated theoretically and experimentally that by selecting the pump laser direction properly one can maximize the coupling between the pump laser and the scarred modes in a liquid-jet quadrupole-deformed microcavity, thereby maximizing lasing efficiency. We directly observed that the output emission emerged from the locations on the cavity surface which correspond to the corners of the unstable periodic orbit, with its direction tangential to the cavity surface via evanescent tunneling mechanism, resulting in collimated directional output.