EFFICIENT K-ALPHA-X-RAY SOURCE FROM FEMTOSECOND LASER-PRODUCED PLASMAS

We have performed a detailed quantitative study of the intense electro n pulse produced by nonlinear absorption during ultrafast laser-solid interaction at near normal incidence. The resulting K alpha x-ray line s have been investigated by time-integrated spectroscopy in the 1-4 ke V range and by Monte Carlo simulations of hot electron energy penetrat ion in Al-SiO2 and Al-CaF2 targets. Calibration of the observed electr on fluence and K alpha line intensities was provided by direct monoene rgetic electron beam interaction with the same target. Optimum conditi ons for hot electron production were obtained by setting the prepulse energy fluence close to the target damage threshold. Results indicate that K alpha lines were produced by a distribution function of hot ele ctrons which carry 12% of the incident laser energy with a characteris tic temperature of about 8 keV. Spectrally and spatially resolved K al pha emission measurements using a cooled charge-coupled-device detecto r demonstrate the scaling capabilities of this x-ray source to energie s in excess of 6 keV.