The experimental images of the sidescattered light from a plasma, created by the multiterawatt laser pulse propagating in a hydrogen gas jet, exhibit clear dependence on both gas jet pressure and laser power. Two-and three-dimensional simulations of wave propagation, in presence of the relativistic electron mass increase and the ponderomotive expel of electrons, have been performed to reproduce the Thomson radiation from the plasma electrons. They show electron cavitation induced by the beam focusing, self-focusing, self-guiding, smoothing of the beam nonuniformities and, at larger power, beam filamentation. A bremsstrahlung model with account of the ionization, heating, expansion, and recombination dynamics of the gas, provides the plasma emission background. Both Thomson emission and bremsstrahlung are required to recover the experimental emission patterns. Among the interpretations, a scenario of laser self-guiding over five Rayleigh lengths can be found for 10 TW laser power and 5ϫ10 18 cm Ϫ3 electron density, which surprisingly disappears at larger powers and densities.
A transmission grating streaked spectrograph (SPARTUVIX) has been developed at the Centre d’Etudes de Limeil-Valenton for measuring the temporal evolution of soft-x-ray spectra in laser-produced plasmas. In this article the ideas behind the instrument are described as well as a description of the actual working diagnostic and its relevant components. This diagnostic has been used to look at the time behavior of x-ray laser emission, and a number of very interesting results have been obtained. A representative sample of these results will also be shown.
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