Resonances observed in the polarization ratio of light scattered at 90° from single optically levitated evaporating droplets are shown to provide a means for continuous high-resolution monitoring of droplet size. Due to the distinctive character of the individual features in the polarization ratio, each experimentally measured feature could be clearly identified with a specific calculated one. For evaporating droplets of glycerol from 6.6 to 11.5 µm in diameter, the sharp features which appeared in the calculations at ~0.03-µm intervals allowed measurement of droplet diameter to a resolution of 0.003 µm.
Thomas R. Lettieri, Wilhelmina D. Jenkins, and Dennis A. Swyt, "Sizing of individual optically levitated evaporating droplets by measurement of resonances in the polarization ratio," Appl. Opt. 20, 2799-2805 (1981)