When dye-doped ethanol droplets are irradiated with an intense pulsed laser beam, the resulting laser emission from individual droplets highlights the liquid-air interface. Photographs of the lasing droplets in the micrometer size range taken in a single 10-nanosecond laser pulse clearly show the dynamic changes in droplet size, shape, and orientation.

Inelastic emission characteristics from individual ethanol droplets (60-microm diameter) containing Rhodamine 6G dye and pumped by a cw laser (514.5 nm) were investigated. Laser emission was confirmed by noting the spectral, temporal, and output-versus-input intensity behavior. The liquid-air boundary of the droplets provides the optical feedback at selected wavelengths corresponding to the morphology-dependent resonances of a spherical droplet.

A new optical technique, based on morphology-dependent peaks in the fluorescence spectra, is-used to determine the evaporation and condensation rates of a linear stream of ethanol droplets. The droplets are monodispersed, in close proximity to one another, and impregnated with fluorescent dye molecules. On irradiation of the droplets with a single N(2) laser pulse, the evaporation or condensation rates can be deduced from the wavelength shift (to the blue or to the red, respectively) of the spectrally narrow (<0.1-nm) structure-resonance peaks in the fluorescence spectra.

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