Experimental characterization of hot electron production under femtosecond laser plasma interaction at moderate intensities

We discuss methods and algorithms of high-temperature laser plasma electron diagnostics based on hard x-ray yield and ionic time-of-flight (TOF) spectra measurements in comparison with the results of direct electronic spectrum recording, with the help of the electrostatic spectrometer. The latter shows clearly the two-component nature of the electron population, arising at femtosecond laser plasma interaction. 'Temperatures' of 200 eV and 6 keV for thermal and hot electronic components, correspondingly, were estimated from this measurement. We show that both ionic TOF measurements and double-channel hard x-ray detection allows the assessment of mean hot electron energy in a single laser shot. The former also provides for estimation of the thermal electron temperature and plasma charge state. Good coincidence between the data obtained from the three methods employed is demonstrated. We also describe how to apply our hard x-ray detection method to the case of relativistic laser plasma interaction, where single shot assessment may become even more essential.