Surface enhanced Raman scattering in whispering gallery mode microresonators

Abstract

In this talk I will discuss surface enhanced Raman scattering in silica microsphere resonators based on whispering gallery mode resonance. Recently silica microspheres have attracted attention as a novel substrate for surface enhanced Raman scattering. Whispering gallery mode resonance has been identified as a major enhancement mechanism, along with other effects such as photonic nanojets. In most of the previous experiments, however, free space pumping of the microsphere has been used, which has low efficiency in coupling to the whispering gallery modes. In our approach, we use a tapered fiber coupler for a highly efficient coupling to the whispering gallery modes. Coupling to the microresonator is monitored using a tunable laser. We observe both pump enhancement and Purcell enhancement in the microresonator. Since the linewidth of the whispering gallery modes is much smaller than that of the Raman peaks, sharp peaks corresponding to the whispering gallery modes are overlaid on top of the Raman spectrum of the bulk material. To demonstrate the system’s potential for Raman analysis, I will present the whispering gallery mode surface enhanced Raman spectrum of rhodamine 6G thin film coated on a microsphere resonator.