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 pul se interaction with solid targets, have been studied for laser intensities in the 10(17)-10(19) W/cm(2) range. The target atomic numbers (Z) extended from Z=13 to Z=73. The measured conversion efficiency at Ag K-alpha emissio n line was 10(-3)% at 5 x 10(18) W/cm(2). It has been confirmed that the ho t electron temperature increased as (I lambda(2))(1/3) and the fraction of laser energy in hot electrons follows scaling law of (I lambda(2))(3/4). (C ) 1999 American Institute of Physics. [S1070-664X(99)02004-2].