Efficient x-ray pulse generation from femtosecond-laser-produced plasma and its application to time-resolved spectroscopy

High-density plasmas created near a solid surface by a femtosecond laser pulse emit ultrashort x-ray pulses that are synchronized to the laser pulse. The spectral and temporal properties of x-rays emitted from a femtosecond laser-produced on metal surface are shown. The minimum pulse duration was <3 ps. More than a 30-fold enhancement of soft x-ray emission was achieved by fabricating an array of nanoholes on an alumina surface. Utilizing a 10-ps soft x-ray pulse, we demonstrated time-resolved soft x-ray absorption measurement of optically excited silicon near its L-II,L-III edge. We found that a laser-pulse irradiation caused a more than 10% increase in soft x-ray absorption near the edge, which recovered within 20 ps.