K α -radiation from relativistic laser-produced plasmas

We present systematic investigations on the generation of titanium K α -radiation ( E = 4.5 keV) from plasmas produced with ultrashort, high-intensity laser pulses. A maximum K α -yield appears at a laser intensity of about 3·10 17 W/cm 2 , corresponding to a plasma electron temperature of a few times the K α photon energy. We observe a second increase in the K α -emission yield at intensities higher than a few times 10 18 W/cm 2 , due to the increase in the K -shell ionization cross-section for relativistic electrons. The intensity dependence of the K α -yield is modeled by an analytical expression, only including cross-section, pathlength and electron energy distribution.