Effects of laser beam smoothing on stimulated Raman scattering in exploding foil plasmas

Time-resolved spectra of backward stimulated Raman scattering (SRS) were measured from the interaction of a 527 nm laser with a preformed plasma. The effect of laser smoothing by spectral dispersion (SSD) was studied using laser bandwidth (Delta lambda/lambda=0.1%) and varying the laser intensity (2-20x10(14) W/cm(2)). A broad SRS spectrum extending to short wavelengths was observed for the high-intensity, Delta lambda/lambda=0 case. Narrow spectra corresponding to the peak plasma density were observed for cases with either high intensity and Delta lambda/lambda similar to 0.1%, or with low intensity and Delta lambda/lambda=0. Simulations of the filamentation process were performed for the conditions of these experiments. The simulations show that laser smoothing stabilizes filamentation for high-intensity interactions, and that filaments are stable without smoothing for low intensity. The predicted onset of filamentation without smoothing correlates with the growth of short wavelength SRS. These experimental results are presented and models are discussed that may help explain the data. (C) 1996 American Institute of Physics.