Population Inversions between n = 5, 4, 3 and 2 levels of He-like Al Plasma Observed by Spatially Resolved X-ray Spectroscopy

Population inversions between N=5, 4 and 3 levels are observed in a 100ps Laser-produced plasma. As a results/ XUV of 42Å~46 Å, 130Å and 305Å corresponding to 3-2, 4-3 and 5-4 transitions are observed experimentally. Relative population densities are determined by measuring the intensities of spatially resolved X-ray line spectra of 6.635Å, 6.314Å and 6.18Å corresponding to the 3-1, 4-1 and 5- 1 transitions, which are normalized by their oscillation strengths. Careful absorption was paid to rule out the effect of reabsorption. Populations were inverted at the region located 50~100μm from the target surface. Laser light was focused into 50μm diameter and amount of inversion was clearly increased when laser intensities was increased. As to the 5-4 and 4-3 inversion, similar result was observed in silicon target, however inversion between n=3 and 2 was not confirmed at these laser intensities. XUV gains are very promising especially as to 5 4 and 4-3 transitions in both target.