Dependence of x-ray yield from aluminum plasma produced by a pair of femtosecond Ti:sapphire laser pulses on pulse time separation

The influence of a prepulse on soft x-ray emission in the range of 50∼200 A from Al plasma produced by 130-fs Ti:sapphire laser pulses was studied at an intensity of 1014 W/cm2 at normal incidence. A prepulse with an intensity of 1013 W/cm2 caused enhancement of soft x-ray emission with a large time separation between prepulse and an intense main pulse. However at 800 nm, a prepulse resulted in reduction with small pulse time separation, contrary to previous reports. This observed trends were qualitatively explained in terms of the absorption dependence on scale length. copyright 1996 American Institute of Physics