Measurement of preheat due to fast electrons in laser implosions

Fast electrons due to the two-plasmon decay instability have been shown to be generated in laser interaction experiments. The purpose of the present e xperiment is to determine the preheat level due to these electrons, using t he K alpha emission from a two-layer, Ti-V, planar target. The target is de signed to separate the contributions of fast electrons and radiation to the observed K alpha intensity. About 0.3% of the incident laser energy is fou nd to be deposited as preheat due to fast electrons. It is shown that the p reheat level can alternatively be determined directly from the hard x-ray c ontinuum without the need to know the electron dynamics; the only required parameters are the total energy in hard x rays and the temperature of the f ast electrons. (C) 2000 American Institute of Physics. [S1070-664X(00)02409 -5].