Abstract
Amplified spontaneous emission of Al ions was observed in a recombining plasma produced by a low-power driving laser of only 2 joules. This lasing was achieved by sharply focusing a pumping glass laser (5 ns FWHM) to a line 40 μm wide and 12 mm long onto a slab target. The spectral lines (time integrated) in the soft-X-rayregion were observed by a flat-field-type grazing incidence spectrograph which axially viewed the plasma with a spatial resolution of 200 μm. The measured gain coefficients are 3.4, 4.5, 3.4, and 3.5 cm-1 for the 105.7 Å (3d-51) and 154.7 Å (3d-4f) in Al XI and for the 123.Å (3d-5f) and 177.8 Å (3d-4f) in Al X, respectively. The gain was observed in a large area of 500μm×600 μm around z=0.8 mm. As Al XI line emissions continue during about 6 ns (FWHM), a soft-X-ray laser resonator is expected to be effective. Electron temperature in the plasma inthe neighborhood of the target was estimated by a filter absorption method to be 400±100 eV, which is hot enough to produce Al11+ ions with high density. It is considered that plasma is sequentially heated up to high temperature by a train of laser pulses of short time intervals.
