STIMULATED BRILLOUIN-SCATTERING IN LONG-SCALE-LENGTH LASER PLASMAS

Brillouin scattering from a preformed, inhomogeneous, expanding plasma has been investigated. Backscattered light near the incident laser wa velength (lambda=1054 nm) from CH planar targets has been spectrally a nd temporally resolved. By varying the: time delay of the interaction beam, the scattering was studied for different plasma conditions. The backscattered light is predominantly blue-shifted and appears before t he peak of the laser pulse. The experimental time-integrated reflectiv ity of backscattered light is in the range of 1%-10% and decreases wit h the plasma density. The time-resolved spectra and total reflectivity were calculated using a theory of convective stimulated Brillouin sca ttering (SBS) in a flowing inhomogeneous plasma combined with a statis tical hot spot model for the interaction beam. The plasma parameters f or these calculations were provided by simulations using a two-dimensi onal hydrodynamic code. The calculated SBS spectra are similar to the experimental observations. The time-integrated reflectivities agree we ll with the experimental results for the higher peak density interacti ons, but are below the observations by orders of magnitude for the low est peak density cases. (C) 1998 American Institute of Physics.