Stimulated Raman and Brillouin scattering, nonlinear focusing, thermal blooming, and optical breakdown of a laser beam propagating in water

Abstract

The physical processes associated with propagation of a high-power laser beam in a dielectric include self-focusing, stimulated Raman scattering, stimulated Brillouin scattering, thermal blooming, and multiphoton and collisional ionization. The interplay between these processes is analyzed using a reduced model consisting of a few differential equations that can be readily solved, enabling rapid variation of parameters and the development of theoretical results for guiding new experiments. The presentation in this paper is limited to propagation of the pump, the Stokes Raman, and the Brillouin pulses, ignoring the anti-Stokes Raman. Consistent with experimental results in the literature, it is found that self-focusing has a dramatic effect on the propagation of high-power laser beams in water. A significant portion of the pump laser energy is transferred to Stokes Raman forward scatter along with a smaller portion to Brillouin backscatter.