High-precision identification of morphology-dependent resonances in optical processes in microdroplets

Abstract

The spectroscopy of the morphology-dependent resonances of a microdroplet has been studied at high precision. The line positions are shown to reveal optical dispersion and permit the refractive index to be determined with sufficient accuracy to provide an estimate of the droplet cooling that is due to evaporation. Comparison of the remaining discrepancies in mode positions for different radial modes indicates a small temperature gradient near the surface. Both the cooling and the temperature gradient are compatible with thermodynamic estimates. The mode quantum numbers are identified with high confidence, and the systematics of the line intensities permit an estimate of the extra radiative loss 1/QL over and above that predicted by Lorenz–Mie theory for a perfect homogeneous microsphere, for example, that which is due to internal scattering, with QL ≈ 2 × 108 for first-order modes.