Whispering gallery mode (WGM) resonators exhibit high quality factor Q and a small mode volume; they usually exhibit high resolution when used as sensors. The light trapped inside a polymeric micro-cavity travels through total internal reflection generating the whispering gallery modes (WGMs). A laser or a lamp is used to power the microlaser by using a laser dye embedded within the resonator. The excited fluorescence of the dye couples with the optical modes. The optical modes (laser modes) are seen as sharp peaks in the emission spectrum with the aid of an optical interferometer. The position of these optical modes is sensitive to any change in the morphology of the resonator. However, the laser threshold of these microlasers is of few hundreds of microjoules per square centimeter (fluence) usually. In addition, the excitation wavelength’s light powering the device must be smaller than the microlasers size. When metallic nanoparticles are added to the microlaser, the excited surface plasmon couples with the emission spectrum of the laser dye. Therefore, the fluorescence of the dye can be enhanced by this coupling; this in turn, lowers the power threshold of the microlaser. Also, due to a plasmonic effect, it is possible to use smaller microlasers. In addition, a new sensing modality is enabled based on the variation of the optical modes’ amplitude with the change in the morphology’s microlaser. This opens a new avenue of low power consumption microlasers and photonics multiplexed biosensors.
Unveiling the Coupling of Single Metallic Nanoparticles to Whispering-Gallery Microcavities
