Optical probing of laser-induced indirectly driven shock waves in aluminum

Abstract

Optical signals from shock waves emerging at a free surface of metals are expected to yield information about the equation of state and the transport and relaxation properties of hot dense plasmas. We present the results of optical measurements on planar shock waves ͑velocity Ӎ22 km/s, pressure Ӎ8 Mbar͒ in solid aluminum which were generated by exposing a miniature sample to intense thermal x rays from a laser-heated cavity. The reflectivity of the free surface of the sample for the light from a probe laser (ϭ532 nm) and the absolute value of its optical emission were simultaneously registered with a 7-ps temporal resolution. For interpretation we used a two-temperature hydrodynamic code which includes the electron heat conduction and electron-ion relaxation and accounts for the nonequilibrium shock structure. The underlying self-consistent model for the equation of state and the transport coefficients of a metal over the relevant range of thermodynamic parameters are described in some detail. The reflectivity decay signal, which yields direct information on the effective collision frequency in the unloading material, and the emission peak, which is sensitive to the heat conductivity and dielectric permittivity of the hot and dense plasma behind the shock front, are well reproduced by the simulations. The emission signals are, however, longer than predicted, possibly due to the residual surface roughness in the experiment. On a longer time scale of 1-2 ns, the emission signal is well described by a simple radiation transport model with the Kramers-Unsöld opacity. ͓S1063-651X͑97͒09007-7͔PACS number͑s͒: 52.25. Fi, 52.25.Mq, 52.25.Rv, 52.35.Tc

Measurement of preheating due to radiation and nonlocal electron heat transport in laser-irradiated targets

“…In previous experimental investigations, target preheating has been measured by optical emission [17][18][19][20][21][22] and reflections at the rear surface 18,21,[23][24][25][26] with both direct drive 17,20-25 and indirect-drive 18,19,26 configurations. However, there is no experimental work on the target preheating for a condition directly associated with the nonlocal electron heat transport.…”

Use of Chemometrics and Laser-Induced Breakdown Spectroscopy for Quantitative Analysis of Major and Minor Elements in Aluminum Alloys

“…Previous work suggests that these matrix effects are reduced, but not eliminated. 1 Many papers have been published on the quantitative analysis of aluminum alloys [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] using univariate prediction models constructed with classical least-squares regression between a dependent variable (signal for an element) and an independent variable (concentration of the element). The drawback with univariate prediction models is that they are sensitive to matrix effects.…”

Line-imaging velocimeter for shock diagnostics at the OMEGA laser facility

“…Active probing techniques can provide a wealth of information on transport properties, primarily through quantitative measurement of optical reflectance. Measurements of target reflectance with active probes have revealed detailed information on electrical conductivities in release profiles [12] and in the shock front [13,14].…”