Showing papers by "Richard Berger published in 1996"
TL;DR: In this paper, the authors investigated the scattering of laser light by SBS and SRS as a function of beam smoothing and plasma conditions in the National Ignition Facility (NIF).
Abstract: Scattering of laser light by stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) is a concern for indirect drive inertial confinement fusion (ICF). The hohlraum designs for the National Ignition Facility (NIF) raise particular concerns due to the large scale and homogeneity of the plasmas within them. Experiments at Nova have studied laser–plasma interactions within large scale length plasmas that mimic many of the characteristics of the NIF hohlraum plasmas. Filamentation and scattering of laser light by SBS and SRS have been investigated as a function of beam smoothing and plasma conditions. Narrowly collimated SRS backscatter has been observed from low density, low‐Z, plasmas, which are representative of the plasma filling most of the NIF hohlraum. SBS backscatter is found to occur in the high‐Z plasma of gold ablated from the wall. Both SBS and SRS are observed to be at acceptable levels in experiments using smoothing by spectral dispersion (SSD).
126 citations
TL;DR: The dependence of the magnitude of stimulated Raman scattering (SRS) on ion-wave damping has been demonstrated in a high-{ital Z} plasma and the measurements are consistent with models in which the amplitude of the SRS-driven Langmuir waves are limited by a secondary decay into ion-acoustic waves.
Abstract: The dependence of the magnitude of stimulated Raman scattering (SRS) on ion-wave damping has been demonstrated in a high-{ital Z} plasma. The ion-wave damping is varied in a well characterized Xe plasma by varying the concentration of a C{sub 5}H{sub 12} impurity. The reflectivity of SRS is observed to be linear with the concentration of the dopant, demonstrating the effect of ion-wave damping on SRS. The measurements are consistent with models in which the amplitude of the SRS-driven Langmuir waves are limited by a secondary decay into ion-acoustic waves. {copyright} {ital 1996 The American Physical Society.}
62 citations
TL;DR: In this paper, the effect of laser smoothing by spectral dispersion (SSD) was studied using laser bandwidth (Δλ/λ=0.1%) and varying the laser intensity (2−20×1014 W/cm2).
Abstract: 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 (Δλ/λ=0.1%) and varying the laser intensity (2–20×1014 W/cm2). A broad SRS spectrum extending to short wavelengths was observed for the high‐intensity, Δλ/λ=0 case. Narrow spectra corresponding to the peak plasma density were observed for cases with either high intensity and Δλ/λ∼0.1%, or with low intensity and Δλ/λ=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 t...
42 citations
TL;DR: The intensity dependent deflection of a laser beam traversing an exploding foil plasma is measured for the first time.
Abstract: The intensity dependent deflection of a laser beam traversing an exploding foil plasma is measured for the first time. An incident {ital f}/8 probe beam exhibits deflection of up to 6{degree} and angular spreading of as much as a 17{degree} cone angle ({ital f}/3.3) as it exits a preformed plasma with significant plasma flow. {copyright} {ital 1996 The American Physical Society.}
34 citations
3 citations