We have demonstrated the sub-10-ps time-resolved measurement of the x-ray absorption fine structure (XAFS)
in laser-excited Si foil by using a femtosecond laser-produced plasma soft x-ray as a probe. We observed a rapid
change and recovery in the absorption structure near its LII,III edge induced by 100-fs laser pulse irradiation
when the laser intensity was in the 109-1010 W/cm2 range. When the incident laser intensity was of the order of
1012 W/cm2, which is higher than the damage threshold, the extended x-ray absorption fine structure (EXAFS)
signals clearly revealed inter atomic distance expansion and structural disordering as well as a change in the
electronic structure caused by the production of liquid Si. We also describe our recent results on spatio-temporally
resolved soft x-ray absorption in an expanding ablated particle cloud from aluminum that was heated with a
1014-W/cm2, 100-fs laser pulse by using an imaging system for time-resolved soft x-ray absorption spectroscopy.
Time-integrated spatially resolved emission spectra of soft x-rays were obtained in the case of 100-fs-laser irradiation of tantalum and aluminum targets by controlling the time intervals between the main pulse and artificial pre-pulse. The intensities of the main pulse and pre-pulse were fixed to 1.3x1016 and 2.0x1014 W/cm2. X-ray intensities were enhanced more than several ten fold at the optimal pulse-separation time of 2 ns. We confirmed that the main emission area for each target was less than 50-μm long from the target surface. In contrast to the small size of main emission area, we observed that line emissions from the aluminum target expanded far from the target.