Hard x-ray emission from intense short pulse laser plasmas

Hard x-ray emission in the range of 100 keV has been measured from plasmas produced by irradiation of solid targets with ps laser pulses up to 7×1017 W/cm2. The experimental data obtained for oblique incidence of p-polarized laser light at different illumination angles are compared to computer calculations, which include the processes of resonance absorption and vacuum heating. The scaling of hard x-ray emission with varying laser flux is consistent with the theoretical model of bremsstrahlung emission of hot electrons. From this, together with an absolute radiation dose measured with calibrated detectors, a transfer of up to 50% of the incident laser energy to suprathermal (∼10...100 keV) electrons is estimated.