J. Phys. IY France 11 (2001) O EDP Sciences, Les Ulis Nickellike and neonlike soft X-ray lasing driven by two 200 ps Nd:glass laser pulses Y. Gu, Yutong Li, Yingjun Li, Y. You, S. Chunyu, W. Huang, S. He, Y. He, L. Lu, X. Yuan, X. Wei, C. Zhang and J. hang' National Laboratory of High Temperature and High Density Laser-Plasma, lnstifute of Nuclear Physics and Chemistry, P. 0. Box 9 19(986), Mianyang 62 1900, China Institute of Physics, Chinese Academy of Sciences, P.O. Box 603(4), Beijing 100080, China Abstract. Soft x-ray lasing at 18.9 nm and 20.3 nm in nickel-like molybdenum and niobium ions has been demonstrated using two 200 ps laser pulses with -0.2TW laser power at 1.053pm from XingGuang I1 laser facility. A comparison has been made of performance of the neon-like chromium soft x-ray lasing at 28.5nm driven by a double 900 ps pulse at 6 TW/cm2, compare to that driven by a double 200 ps pulse at similar iriadiance. The 900 ps pulse duration was found to be able to provide stronger emission and narrower divergence of neon-like chromium sofi x-ray lasing. 1. INTRODUCTION One of the major objectives for the development of x-ray lasers is to reduce the energy significantly to make x-ray laser widely available. Over last ten years, great progresses have been made in this respect. In terms of driving pulse configuration, single, double, multiple pulse and traveling-wave pumping technique [l] were developed. The most impressive achievement is the introduction of prepulse technique [2]. In the collision excitation scheme, the prepulse technique reduces the drive energy and enhances the J=0-1 lasing line dramatically. We have demonstrated soft x-ray lasing at 32.6nm in neon- like titanium ions driven by 40 J of energy using prepulse technique [3]. A shadowgraph experiment using this laser was conducted in which a copper mesh was imaged [4]. For x-ray laser applications such as Moore deflectometry [5] and interferometer [6] in plasma diagnostics, soft x-ray laser sources at a wavelength shorter than 30 nm is desirable because the higher density region can be probed and the multilayer mirrors can have higher reflectivity. In the hope to develop a x-ray laser at a wavelength shorter than 30 nm driven by small energy Nd: glass laser, we explored neon-like chromium laser at 28.5~1, nickel-like molybdenum laser at 18.9nm and niobium laser at 2 0 . 3 ~ 1 as our potential x-ray sources for future application experiments. 2. EXPERIMENTS AND RESULTS 2.1 Nickel-like molybdenum and niobium x-ray laser experiments One of the efficient ways of producing lasing at shorter wavelength is provided by nickel-like ions, in which the pump intensity can be reduced significantly because the quantum efficiency of the nickel-like system is much higher than that of the neon-like system. Much effort has been devoted to developing nickel-like x-ray lasers [l 1-14]. In the experiments [l l] and [12], the saturation of nickel-like Ag and Sm was demonstrated at 14nm and 7 nrn with an irradiance of 2 0 - 4 0 ~ ~ 1 c m ~ . A small-scale x-ray laser based on the collision excitation scheme in nickel-like low-Z ions was first proposed by Hagelstein [16]. According to the author, for molybdenum an electron temperature near 150 eV and density near 1.2~10'~ cm-) were optimal conditions. A preliminary experiment to observe the gain in nickel-like molybdenum was done by using a series of 80 ps pulses separated by 7.5 ns, however, the lasing is too weak to be identified [l 71. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:2001231