[en] This report is a detailed proposal for a short pulse, short wavelength, optical probe which can be synchronized with either GDL or OMEGA. Typical probe laser parameters are lambda approx. 2000 A, t approx. = 2 ps, with an energy of several hundred μJ and synchronization of 20 to 50 ps. The present design is based on detailed experimental work done over the past two years in the Picosecond Group at LLE

No abstract available

[en] Experimental results are presented for the interaction of high energy uv (350 nm) lasers with plasmas. The measurements show (1) high absorption efficiency via collisional processes, (2) inhibited thermal transport similar to that observed at longer wavelengths, (3) greatly reduced preheat from fast electrons, and (4) evidence for saturated values of Raman scattering and 2-plasmon decay instabilities. All these results are encouraging for the use of shorter wavelength lasers for inertial fusion

[en] Detailed studies of the ion acoustic parametric decay instability have been made. Theoretical and particle simulation results indicate these instabilities are important in long scale length plasma irradiated by moderate intensity laser light (10'' ≤ Iλ²/T/sub e/ (W/cm²) (μm²)/(keV) ≤ 5 x 10¹⁴). Laser light (λ₀ ≅ 1/2 μm) is focused onto a CH target. The parametric decay instability has been measured by detecting the emission spectrum at frequencies near 2ω₀. The experimental results clearly indicate that this parametric instability is important for short wavelength (1/2 μm) laser light irradiation. The threshold of the parametric instability (λ₀ = 1/2 μm) was only slightly higher than that of 1 μm laser case. The measured wavelength shift of the Stokes component (λ₀ = 1/2 μm) compared very well with the 1 μm laser results

[en] A model of Raman scattering in inhomogeneous laser produced plasma is described, which invokes enhanced Thomson scattering. The enhancement is due to pulses of hot electrons arising from laser-plasma interactions at the critical or quarter-critical surfaces. A simple model predicts the locations of two enhanced frequency bands, one between ω₀ and ω₀/2, and the other between 2ω₀ and ω₀. The model is shown to fit the results of eight experiments, including a new experiment using the 6-beam Omega laser facility, converted to 351 nm. In this latter experiment, simultaneous measurement of the upscattered and downscattered bands is carried out, and good agreement is found with the enhanced Thomson model. 19 refs., 24 figs

[en] OAK-B135 All Solid State Optical Pulse Shaper for the OMEGA Laser Fusion Facility. The authors have developed an all-solid-state, compact, computer-controlled, flexible optical pulse shaper for the OMEGA laser facility. This pulse shaper produces high bandwidth, temporally shaped laser pulses that meet OMEGA requirements. The design is a significant simplification over existing technology with improved performance capabilities

[en] The onset of an instability, such as the 2ω/sub p/ at the n/sub c//4 surface, usually leads to wave breaking and the emission of hot electron pulses which can profoundly influence instability thresholds and scattering behavior elsewhere in the plasma. In particular, enhanced Thomson scattering (via the plasma line) can occur, and this has been used to explain the observation of the SRS instability well below the theoretical threshold. A simple model of the hot electron pulses based on measured values of the hot and cold electron temperatures, T/sub h/ and T/sub c/, has yielded good agreement with experimental observation of the Raman spectral frequency bands. The agreement has continued, even for experiments which are clearly above the SRS threshold, with the enhanced noise likely acting as a ''seed'' for the SRS growth. We will show details of the successful comparison of this theory with six experiments carried out on SHIVA, ARGUS, NOVETTE(2), and GDL(2), and also with an upscattering feature seen at Garching. In addition, a recent experiment using 6 beams of OMEGA (at 0.35μ) will be discussed, and compared with the theory. The report is comprised of viewgraphs of the talks

[en] The authors report the results of single beam irradiation of thin CH foils at laser intensities of 10¹³ to 10¹⁵ W/cm² in 0.8 ns pulses containing 20 to 50 J of 350 nm and 1054 nm light. They also discuss the hydrodynamic efficiency, thermal transport and preheat in these targets. Included is the measurement of the ion blowoff energy distribution and velocity. The efficient acceleration by short wavelength radiation causes target displacements comparable to the spot size resulting in two-dimension effects. The results are adequately modeled with the 2-D hydrocode SAGE using a flux limiter of f=0.04

No abstract available

[en] The two-plasmon decay of light propagating in filaments in a laser plasma and the resulting 3 omega₀/2 light emission is discussed using a simplified model. Experimental observations are consistent with the predictions of the model. Implications for use of the 3 omega₀/2 doublet splitting as a temperature diagnostic are discussed