Asymptotic estimates of threshold power for laser excitation of thermal instability for high-Q resonant modes in water aerosol droplets

Abstract

We have calculated the threshold powers for the thermal oscillatory instability as functions of the diffraction parameter and the laser pump wavelength for high-Q water aerosol droplets. The integrated overlap coefficients of the thermal and electromagnetic modes have been estimated by asymptotic methods. We have found the threshold power of the thermal instability to be comparable in order of magnitude to that of the stimulated Raman scattering and the thermal instability in spherical resonators of fused silica, 0.1 mW at the pump wavelength λp = 0.532 μm for a droplet radius of 5.3 μm. Measurements and estimations of the threshold power are of importance in applications as an additional method for remote temperature measurement and control of the evaporation-condensation rate for a droplet containing photoactive impurities, dyes, and polymer nanoparticles, based on the eigenfrequency shift in the stimulated Raman scattering and lasing spectra.