Prepulse dependence of soft X-ray spectra from plasmas created by femtosecond IR laser pulses on solids

We report a strong prepulse dependence of the soft X-ray emission from plasmas created by 150 fs Ti:Sapphire laser pulses on solids. By reflecting a portion of the main pulse, a prepulse was generated, variable in time delay and relative intensity. The laser pulses were focused onto plane samples of aluminum and vanadium with a main pulse intensity of about 2.5 × 10¹⁶ W/cm². With no prepulse, practically no soft X-ray radiation from Al⁹⁺ and Al¹⁰⁺ was observed, whereas a prepulse to main pulse ratio of about 0.5%, with the prepulse preceding the main pulse by more than 2 ns produced the strongest soft X-ray output.