Optical properties of semiconductor microspheres fabricated via laser ablation in superfluid helium

We fabricated semiconductor zinc oxide microspheres via the pulsed laser ablation in the superfluid helium. The fabricated microspheres have a smooth surface and act as an optical microcavity showing whispering gallery mode resonances. We observed the inner structure of the microspheres after milling the part of the microspheres using focused ion beam. The observation of the milled surface reveals that some of the fabricated microspheres include voids. In particular, the larger microspheres tend to have voids inside themselves. Furthermore, we demonstrated that the microspheres with voids can have a high quality factor whispering gallery mode resonance if the void is positioned near the middle of the volume.