PREHEATING STUDY BY REFLECTIVITY MEASUREMENTS IN LASER-DRIVEN SHOCKS

A study on preheating effects in laser-driven shock waves is presented . Two different diagnostics were used: the color temperature measureme nt deduced by recording the target rear side emissivity in two spectra l bands, and the rear surface reflectivity measurement by using a prob e beam. In order to test the response of the two diagnostics to the pr eheating, three types of targets characterized by different radiative properties were used. The greater sensitivity of the second diagnostic compared with the first was demonstrated. A model which calculates th e reflectivity using a one-dimensional hydrodynamic code data was deve loped. In this model, the wave propagation equations in the expanding plasma using an appropriate model for the electron-ion collision frequ ency applicable to the cold solid-hot plasma transition were solved. T he comparison between the calculated and measured reflectivities allow s us to estimate the preheating process. (C) 1998 American Institute o f Physics. [S1070-664X(98)01606-1]