Optical microcavity sensing: From dispersive to dissipative interactions

Detection of single nanoscale objects is highly desirable for applications in various fields, such as in early-stage diagnosis of human diseases and in environmental monitoring. High-Q microcavities, which can significantly enhance light-matter interactions, provide ideal platforms for label-free, ultrasensitive detection of single nano- objects. In the first part of this talk, we report the experimental demonstration of single nanoparticle detection using either resonance mode broadening or microcavity Raman laser splitting. For the latter, by monitoring the step changes in beat frequency of the two split Raman mode lasing, detection of single 20-nm-radius nanoparticles is realized in an aqueous environment. In the second part, we propose and demonstrate to detect single lossy nanoparticles using the dissipative interaction in a high-Q toroidal microcavity. In experiment, detection of single gold nanorods in aqueous environment is realized by monitoring simultaneously the linewidth change and shift of cavity mode. The experimental result shows a good agreement with the theoretical prediction.