The geometric optics model of light scattering from droplets is based on the interference of the reflected and refracted light. Although the relationships are regularly quoted, we have found that the assumptions in the underlying derivations are incorrect. In this rapid communication, we derive the correct optical path difference between reflected and refracted beams scattered from a droplet. Furthermore, we show that the standard form used for the scattering factor relating the fringe separation to the droplet diameter is wrong - we derive the correct analytical result, which leads to a correction in droplet-size calculations based on optical measurements.
Golombok, M., Morin, V., & Mounaim-Rouselle, C. (1998). Droplet diameter and the interference fringes between reflected and refracted light. Journal of Physics D: Applied Physics, 31(18), L59-L62. https://doi.org/10.1088/0022-3727/31/18/001