Experiments have been performed to measure the rate of laser-induced damage growth at the rear surface of fused silica windows at 1064, 1053 and 351 nm. One test bench delivered 9 ns monomode gaussian pulses at 10 Hz and 1064 nm. The size of the focused beam on the sample was a few mm2. Another test bench delivered 2.5 ns single or multimode pulses at 1053 and 351 nm. The focused spot on the sample was a few cm2. We compare and discuss our laboratory experimental results, the larger scale ALISE laser data and other results obtained at LULI.
Variable experimental conditions were used to measure the occurrence of front surface, rear surface and filamentation damage in synthetic fused silica windows. Experiments were performed at 355 nm with a table-top beam of mm-size, and at 351 nm with ALISE laser, a 100 J installation. The 351 nm beam was about 3 cm wide at the entrance surface; it was single-mode temporally, with or without a frequency modulation which has the function of widening the spectrum to decrease Stimulated Brillouin Scattering. The 355 nm was single-mode temporally. Thin windows showed very scarce front damage and no filament damage at intensities which cause a high density of rear surface damage. Without any spectral widening, the thicker windows (4.3 cm) showed appreciable amount of front surface damage; filaments were observed and but no filaments. When a spectral modulation was added, front surface damage vanished, filaments and rear surface damage were observed.
We present the final optics design of the Megajoule Laser using high efficiency transmission gratings at 1053 nm and 351 nm for broadband tripling, wavelength filter, laser diagnostics sampling and focusing on target. We also present a 1:3 scale prototype of our optical system and we summarize the experimental results obtained during the year of 1998.
Design optimization of the 1 .8 MJ, 500 TW National Ignition Facility (NIF) laser has
proceeded with the use of a suite of new computational models. Cost-effectiveness of alternative
fundamental architectures was considered using CHAINOP. A very fast, lumped-element
energetics code, CHA1NOP includes an extensive cost database, a runtime choice of optimization
algorithm, and a set of heuristic rules for diffraction and nonlinear effects and for operational
constraints. Its ability to flexibly consider many alternative configurations at a few seconds per
chain made it the ideal "first-cut" tool for narrowing the investigation to the switched, multi-pass
cavity architecture that was chosen.
We present a high yield method of broadband frequency mixing which relies on a matching of induced phase-modulation in order to overcome the normal phase-matching limitations. We analyze it for two cases of linear and sine chirpings.
The Phebus laser system has been mainly devoted to plasma physics experiments such as implosion and hydrodynamical instability studies since it was completed in 1985. But during the last two years, the three Phebus beamlines (2 main beams and a backlighter beam) are also utilized to perform some laser physics studies in view of the megajoule laser project. The goal of the laser physics experiments conducted at the Phebus facility in 1994-1995 is to validate some design issues of the megajoule laser project concerning namely power balance and frequency conversion.
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