Nanocylinder-array structure greatly increases the soft X-ray intensity generated from femtosecond-laser-produced plasma

In order to increase the soft X-ray conversion efficiency for the femtosecond-laser-produced plasma, we adopted a nanocylinder-array structure target. Gold nanocylinder-array targets with 70--90 nm cylinder diameter and 100 nm cylinder pitch were made. A continuous smooth soft X-ray spectrum adequate for X-ray absorption spectroscopy was obtained. An around 20-fold soft X-ray (7--20 nm) fluence enhancement compared with a flat-surface gold foil target was obtained when the cylinder height was 18 *mm. X-ray (>0.06 keV) pulse duration was 17 ps, which is much shorter than that obtained by using the pre-pulse technique. The X-ray pulse peak intensity was 7-fold higher than that of a gold foil target.