Large gain in nickel-like iron and nickel-like tin and silver plasmas produced by multiple-laser-pulse irradiation

This work has consisted in demonstrating that high gain can be achieved by pumping x-ray lasers (XRL) with a combination of a high intensity and short duration driving pulses (∼100 ps). Short pulses are very well suited for pumping collisional XRL since a high lasant ion density, electron density and temperature can be achieved simultaneously. We have successfully tested this pumping scheme on the 4d-4p (J=0-1) transition of Ni-like tin (λ∼11.93 nm) and silver (λ∼13.89 nm) as well as on the 3p-3s (J=0-1) Ne-like iron (λ∼25.5 nm) at an intensity of ∼2×10¹³ Wcm^-2 (130 ps in duration). The driving laser (λ=1.06 μm) was composed of three pulses (a prepulse and two main pulses). Large amplifications were demonstrated in tin and silver (respectively GL∼12 and GL∼16). Finally, the saturation of the 3p-3s (J=0-1) transition of Ne-like iron at 25.5 nm was achieved on both pumping pulses, using a prepulse of 10⁹ Wcm^-2. A gain coefficient of 15±3 cm^-1 (GL∼26±5) on the first main pulse and 12±1cm^-1 (GL∼23±2) on the second one was measured.