Observation of sharp resonances in the spontaneous Raman spectrum of a single optically levitated microdroplet

Sharp resonances have been observed in the spontaneous Raman spectra of single, optically levitated microdroplets. The droplets, 10 to 35 μm in diameter, were suspended by a CW argon laser beam which also served as the Raman excitation source. Experiments with dioctyl phthalate (DOP) and silicone oil confirmed that all Raman bands present in the bulk liquid spectra were also observable in the levitated droplet spectra, in agreement with previous micro-Raman studies of droplets on substrates. However, superimposed on the spectra of the levitated droplets was a series of sharp features not present in the bulk liquid spectra. Time-resolved experiments with growing DOP droplets showed that the sharp Raman features have the same origin as the elastic light scattering and flourescence resonances observed in previous studies of microspheres and fibers.