ator formed by a dye-doped pendant drop was measured by addition of polymer particles to the dye solution to enhance the elastic-scattered light of the lasing inside the pendant drop. A theory that connects wave and ray pictures in dealing with the cavity resonance is used to calculate the internal intensity distribution. The experimental and theoretical results are in good agreement for sufficiently large densities of scattering particles, such that the cavity mode efficiency φ is～1 for all resonant modes.

The enhancement of stimulated Raman scattering (SRS) of weak-gain Raman modes in pendant drops is accomplished by overlapping Stokes wavelengths of the Raman modes with the Rhodamine 640 dye-lasing gain region (called the gain-overlap method). The dye concentration and the pumping intensity of frequencydoubled Nd: YAG lasers determine the efficiency of the enhancement. We apply the gain-overlap technique at optimal dye concentration and pump intensity to probe minority species in pendant drops formed by binary mixtures. The limits of detectable concentrations of the minority species, methanol in methanol-ethanol and ethanol in ethanol-water (dye-doped) mixtures, are much less than those in undoped mixtures. The smooth fluorescence-lasing spectral curves emitted from dye-doped pendant drops reduce complications in distinguishing SRS signals from quasi-periodic fluorescence-lasing spectra in microdroplets.

We have reduced the lasing threshold of a circular resonator, formed by a dye-doped pendant drop, by changing its shape from a circle to an oval. This phenomenon can be explained by the decrease of the number (p) of modes that support lasing in the resonator. A theory that connects wave and ray pictures in dealing with the cavity resonance is used to estimate p and its dependence on the eccentricity of an oval-shaped resonator. The measured lasing threshold and the calculated p have a linear relationship in agreement with our prediction.

The lasing properties of an oval-shaped resonant cavity (ORC) with a continuously variable aspect ratio have been studied. The ORC was formed with a dye-doped pendant drop placed inside a variable static electric field. When the drop ORC was pumped by a nitrogen laser, lasing from the ORC was found to have strong directional emission characteristics and an intensity enhancement factor as great as 19.5. Calculated results of light rays escaping from ORC's by refraction are in good agreement with the experimental data.

The pendant drop technique has been used for compressing and expanding a monolayer film. Both the surface density and the molecular orientation of the surfactant on the surface of a pendant drop can be determined by a polarized fluorescent image for a surfactant molecule with a chromophore. The calculation based on the model developed matches the experimental results on octadecyl rhodamine B very well.