High-Intensity and High-Energy Lase Interactions with Single Droplets

During the three years of ARO support, significant progress has been made toward furthering the understanding of high-intensity laser beam interactions with single liquid droplets with radius, a, much larger than the input laser wavelength (input). Our research efforts can be divided into two parts: (1) laser-induced breakdown (LIB) of droplets; and (2) nonlinear optical effects in droplets. One part of our research was directed toward the optical diagnostics of the plasma associated with the laser-induced breakdown (LIB) processes. We developed several spectroscopic techniques that are capable of providing spatially and temporally resolved measurements of the plasma emission and transmission. The propagation speed and the optical transmission of the breakout plasma from the droplet shadow face and from the illuminated face are determined. The relative heating of the atoms in the plasma is extracted from atomic emission intensities at two different wavelengths. The other part of our research was directed toward the following nonlinear optical effects: (1) the generation of stimulated Brillouin scattering (SBS) in simple droplets; (2) the determination of the angular pattern of stimulated Raman scattering (SRS); (3) the two-photon excitation of lasing droplets; and (4) the modification of the standard nonlinear wave equations to describe the growth and decay of nonlinear waves in droplets.