Nonlinear Optofluidic Processes in Microdroplets

High quality (Q) factor whispering gallery modes (WGMs) can induce nonlinear effects in liquid droplets through radiation pressure, light scattering, thermocapillarity, Kerr nonlinearity, and thermal effect. In our recent studies published in Physical Review E, we investigated such effects on a micron-sized liquid spherical resonator. In the first study, numerical analyses based on the boundary element method helped to quantify the deformation of the droplet under the radiation pressure. We showed that the nonlinear optofluidic effect induced by the radiation pressure is stronger than the Kerr effect and the thermal effects. We further confirmed the possibility that it may only take a few photons to produce measurable WGM resonance shift through radiation-pressure-induced droplet deformation. The effect of the scattering force on the interfacial dynamics of the droplet was quantified in the second study. The interface deformation produced by the thermocapillarity as a result of the WGM energy absorption and temperature increase was also explored. We developed a boundary element program to calculate the fluid motion and quantify the nonlinearity induced by the optical scattering force and thermocapillarity. Our work provides a numerical tool for the study of optofluidic phenomena in liquid microdroplets.