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 experiment is to determine the preheat level due to these electrons, using the Kα emission from a two-layer, Ti–V, planar target. The target is designed to separate the contributions of fast electrons and radiation to the observed Kα intensity. About 0.3% of the incident laser energy is found to be deposited as preheat due to fast electrons. It is shown that the preheat level can alternatively be determined directly from the hard x-ray continuum 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 fast electrons.