Electron heating in high intensity CO2 laser‐plasma interaction

Detailed measurements of heated electron distributions generated in a short density scale length 10.6 μm laser plasma interaction in the intensity regime 1012≲I(W cm−2)≲1014 are reported. Maximum electron energies up to 600 keV observed in this study appear to be inconsistent with characteristic maximum energies of electrons generated by resonant absorption in the warm plasma wave breaking limit. Furthermore, heated electron distributions from foils of thickness much less than the hot electron mean‐free‐path as well as from different Z targets suggest that reheating of very energetic electrons by multipassing through the resonant region does not occur; rather the highest‐energy electrons are preferentially accelerated in the backward direction with very large single pass energies. Plasma instabilities at the quarter critical as well as those at the critical are thought to be responsible for the generation of the high‐energy electron component. Finally, these studies show that the electron emission spectra are sensitive to the electrical properties of the target support structure.