<title>Short x-ray pulse generation towards time-resolved spectroscopy</title>

The soft x-ray generation properties for both flat targets and structured targets such as nanohole-alumina and Au- nanocylinder are evaluated. The experimental results for flat metal targets have revealed the fundamental properties of soft x-ray such as broadband continuum spectra and short pulse duration of less than 3 ps. By adopting structured targets such as nanohole-alumina and Au-nanocylinder targets, a more than 30 fold enhancement of x-ray generation yield is achieved compared with that for flat targets of the same materials with a slight increase of pulse duration, less than 20 ps. Then, the duration of soft x-ray pulse from femtosecond (fs) laser produced W plasma was measured by using cross-correlation method. In the experiment, we measured the transmission spectra of short soft x-ray pulse produced by main fs optical pulses through ionized Kr gas by probe fs optical pulses as a function of the time delay between main and probe fs optical pulses. The pulse duration of 4 ps was observed for soft x-ray at 15.6 nm of W plasma. The time-resolved measurement of the inner-shell absorption change of Si during the irradiation with a high-intensity fs optical pulse is achieved by using a picosecond soft x-ray pulse as a probe pulse in pump-probe experiments. A more than 5% increase in the absorption of Si membrane at near the LII,III edge (around 100 eV) was observed. The recovery time of the absorption change was measured to be about 20 ps. From these experimental results, this absorption change is assumed to be the bandgap renormalization of Si.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.