Transient collisional excitation X-ray laser experiments on P102 laser at CEA-LV

Recent experiments, performed at the C.E.A./Limeil-Valenton P102 laser facility on the Ni-like transient collisional scheme, are reported in this paper. They mainly aimed at enhancing the efficiency and improving the optical properties of the already demonstrated 4d J = 0/4p J = 1 Ag¹⁹⁺ x-ray laser at 13.9 nm. The now classical 2-stage traveling-wave irradiation of slab targets was used, the illumination sequence being constituted of a long (600 ps) low-flux (0.5-11 J) laser pulse followed (200 ps later) by a short (<1 ps) high intensity (1-20 J) one. The work novelty was the use of frequency-doubled pulses, either for the pre-forming or the pumping one. Various combinations (ω-ω, 2ω-ω, ω-2ω) have been investigated in terms of lasing performances. High gains, around 34/cm, have been measured and saturation achieved for target lengths above 4 mm. A strong enhancement, up to a few μJ, of the x-ray laser output has been observed, due to traveling-wave irradiation method, while the emission duration was decreased to less than 10 ps, resulting in a 300 kW source. Moreover, under specific laser conditions, a second lasing line at 16 nm was detected. Finally, the possibility of cavity operating transient collisional x-ray lasers has been demonstrated.