Observation of Soft X-Ray Amplified Spontaneous Emission in a Recombining Si Plasma Pumped by a Low-Power Laser

Amplified spontaneous emissions of Li-like ions were observed in a recombining Si plasma which was produced by a Nd-glass laser of table-top size. The small signal gain coefficient of Si XII 3d-5f (88.84 Å) was evaluated at 0.9 cm-1, and the emissions of Si XII 3d-4f (130.02 Å) and 3p-5d (87.36 Å) transitions show small amplifications. The driver laser pulse has a time envelope of 4 ns-FWHM (full width at half maximum) and contains several short pulses of about 120 ps-FWHM with time intervals of about 350 ps. The average irradiation power density of a short pulse was estimated to be only 5×1011 W/cm2.