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.
Ultrahigh-quality whispering gallery mode optical microresonators have been studied for their use as highly sensitive sensors. In this talk, we discuss the use of microsphere microresonators in Raman spectroscopy for interrogating particles adhered to the surface of the resonator. An external cavity diode laser is tuned to a resonant high-Q mode and the circulating optical field experiences a large buildup, resulting in enhanced Raman scattering. Here we present studies of Raman scattering spectroscopy of single particles. Raman sensing with different Q's is discussed.
The idea of creating photonics tools for sensing, imaging and material characterization has long been pursued and many achievements have been made. Approaching the level of solutions provided by nature however is hindered by routine choice of materials. To this end recent years have witnessed a great effort to engineer mechanically flexible photonic devices using polymer substrates. On the other hand, biodegradability and biocompatibility still remains to be incorporated. Hence biomimetics holds the key to overcome the limitations of traditional materials in photonics design. Natural proteins such as sucker ring teeth (SRT) and silk for instance have remarkable mechanical and optical properties that exceed the endeavors of most synthetic and natural polymers. Here we demonstrate for the first time, toroidal whispering gallery mode resonators (WGMR) fabricated entirely from protein structures such as SRT of Loligo vulgaris (European squid) and silk from Bombyx mori. We provide here complete optical and material characterization of proteinaceous WGMRs, revealing high quality factors in microscale and enhancement of Raman signatures by a microcavity. We also present a most simple application of a WGMR as a natural protein add-drop filter, made of SRT protein. Our work shows that with protein-based materials, optical, mechanical and thermal properties can be devised at the molecular level and it lays the groundwork for future eco-friendly, flexible photonics device design.