Synthesis of ZnO micro-spheres by laser ablation and their application to refractive sensor

The microsized resonators have attracted attention as a sensing device. The resonance mode called whispering gallery mode (WGM) arise from light confinement within a resonator via total internal reflection and has high Q factor. The WGM spectrum shifts in response to the refractive index change surrounding of the resonator. These WGM resonators are generally made from silica or polystyrene, so that they require to guide light into the resonators using a coupling fiber. In addition, the resonators have a limitation on the refractive index of the surrounding materials, which must be less than that of the resonator, or light can not be confined in the resonator. On the other hand, we have succeeded in fabricating ZnO microspheres by a simple laser ablation method in air. In addition, ultraviolet WGM lasing from the photoexcited ZnO microsphere have achieved, which does not need to guide light and enable to deal with high refractive indices up to that of ZnO. In this study, we investigated surface refractive index dependence on the oscillation peak of a photoexcited ZnO microsphere. (author)