Interaction of a high intensity laser with micrometer size liquid droplet

The mechanisms of laser-induced breakdown of transparent liquid droplets was studied. The interaction of the laser field with the droplet results spatially in an internal and near-field intensity enhancement which can significantly lower the laser-induced gas breakdown threshold. In order to study these problems, a novel technique of spatially-resolved laser-induced breakdown spectroscopy was developed. The laser-induced breakdown of droplets is initiated by generating the priming electrons through multiphoton ionization followed by cascade avalanche ionization at two locations: (1) inside the droplet near the shadow face where exists a 10$sp2$X intensity enhancement; (2) outside the shadow face where exists a 10$sp3$X intensity enhancement. The emission spectra of plasma show that the electron density is about 10$sp{18}$ cm$sp{-3}$ in the shadow side plasma and 10$sp{16}$ cm$sp{-3}$ in the illuminated side plasma. A temporally and spatially resolved technique by using a streak camera was used to study the development of stimulated Raman scattering, plasma formation, and propagation characteristics of optical detonation waves. Stimulated Raman scattering was observed to be quenched by the laser-induced internal plasma. The plasma pressure (360-1440 atm) and temperature (15-65 $times$ 10$sp3$ $sp0$K) just behind the shock front were deduced from the measured plasma front velocity. The intensity dependent plasma front velocity indicates that a fast ionization wave was observed in our experiments.