TARGET ATOMIC-NUMBER EFFECT ON THE DURATION AND CONVERSION EFFICIENCYOF ULTRASHORT X-RAY PULSES

High-density plasmas produced by 400 fs, 10(18) W/cm(2) laser pulses a re characterized with a transmission grating spectrometer coupled to a n x-ray streak camera. Conversion efficiencies and durations of the so ft x-ray emission in the 0.1-1.2 keV energy range are analyzed for dif ferent target materials (Fe, Cu, Mo, Ta, and Pb). Our results show tha t the x-ray emission duration is constant for the different materials, with an average value of 4 and 5.7 ps in the 0.8-1.2 keV and 0.2-0.3 keV ranges, respectively. The converstion efficiency is optimal for a Ta target and is about 0.3% for both energy ranges. (C) 1996 American Institute of Physics.