EFFECTS OF AN ULTRASHORT PREPULSE ON SOFT-X-RAY GENERATION FROM AN ALUMINUM PLASMA PRODUCED BY FEMTOSECOND TI-SAPPHIRE LASER-PULSES

The influence of a prepulse on soft X-ray emission in the range of 50- 200 Angstrom from an aluminium plasma produced by 130 fs Ti:Sapphire l aser pulses with an intensity of 10(14) W/cm(2) at normal incidence is studied. An ultrashort prepulse with an intensity of 10(13) W/cm(2) s ignificantly enhances soft X-ray emission when there is a long time se paration ( > 100 ps) between the prepulse and an intense main pulse. I t is also observed for the first time that a prepulse with a short pul se time separation can slightly reduce soft X-ray emission, contrary t o the previous work done using 248 nm laser pulses. This can be explai ned qualitatively in terms of the dependence of absorption on the leng th scale.