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 observed lasing from the rim of dye-doped ethylene glycol pendant drops. Sptatial-resolved spectral measurements show that the lasing wavelength varies along a vertical rim of the drop. Time-resolved measurements indicate that lasing precession occurs within the drop. Various lasing patterns due to lasing precession are explained. The measured precession periods for different pumping points are in good agreement with the calculated values based on morphology-dependent resonance theory.

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.

Highly sensitive elemental analysis of lead carbonate colloids was demonstrated by two-pulse laser-induced plasma spectroscopy. The first laser pulse created a vapor plume with the particulates concentrated in space because of their slower propagation. They were then ablated by an ArF laser pulse that efficiently atomized and excited the lead analyte. The lead emissions were much enhanced, while the background continuum interference was minimized. The detection limit for lead was shown to be 14.2 ppb, compared with 13 ppm achieved by conventional laser-induced breakdown spectroscopy of lead ions in water and 210 ppb for lead aerosols.