The evaporation of liquid droplets in sprays call be altered by interactions between closely spaced particles. We discuss a nonintrusive optical measurement technique that is based on the optical cavity resonances of the droplets to determine droplet sizes and evaporation rates, The addition of small amounts of Rhodamine 6G laser dye into ethanol or ethanol/acetone acetone mixture droplets allows the droplets to lase at discrete wavelengths that correspond to the spectral positions of the droplet-cavity resonances, Measurements of the cavity resonance shift as the droplet evaporates permits determination of droplet size changes with a sensitivity of I nm in droplet radius change for droplets with a radius of 40 mu m. We have determined the variation in evaporation rates among the leading and trailing droplets within a single segmented flowing stream, as well as between adjacent droplets that are flowing within a closely spaced 3 x 3 square array of continuous streams, Qualitative fluorescence images of the vapor produced by a continuous single stream of flowing acetone droplets demonstrate the existence of a vapor trail generated by the leading droplets flowing at 10 m/s.