Hard x-ray emission in high intensity femtosecond laser–target interaction

Hard x-ray spectra (10–100 keV) created in high contrast, 400 fs, laser pulse interaction with solid targets, have been studied for laser intensities in the ${10}^{17}{\text{–10}}^{19} {\mathrm{W/cm}}^2$ range. The target atomic numbers (Z) extended from $\text{Z=13}$ to $\text{Z=73.}$ The measured conversion efficiency at Ag $K_{\alpha }$ emission line was ${10}^{\text{−3}}\%$ at ${\text{5×10}}^{18} {\mathrm{W/cm}}^2.$ It has been confirmed that the hot electron temperature increased as ${\mathrm{(I\lambda }}^2{)}^{\text{1/3}}$ and the fraction of laser energy in hot electrons follows scaling law of ${\mathrm{(I\lambda }}^2{)}^{\text{3/4}}.$