Research On Temporal Characteristics Of 69.8nm Soft-X-ray Laser Pumped By Capillary Discharge

X-ray laser has an extensive prospect because of its specifications, such as short wavelength, high peak power and short pulse duration. Since Rocca group obtained 46.9nm soft-x-ray by electron collisional excitation scheme pumped by capillary discharge for the first time in 1994, many scientific groups have joined the ranks of the research of capillary discharge-pumped soft-X-ray laser. Currently, Ne-like Ar 46.9nm, Ne-like Ar 69.8nm has been achieved taking advantage of capillary discharge pumping scheme. The research of Ne-like Ar 46.9nm laser is relatively mature, a series of reports have been published about its properties. While the study on Ne-like Ar 69.8nm laser which has the same gain medium(Ar⁸⁺) with Ne-like Ar 46.9nm have been gradually proceeding since it had been found in 2011 by our group. There is rarely article about its temporal characteristics. In this paper, the research on temporal characteristics of the Ne-like Ar 69.8nm soft-X-ray laser is studied theoretically and experimentally.In theory, the radius and speed of plasma column during the Z-pinch process under different initial Ar gas pressure conditions have been calculated utilizing snow plow model. In addition, the FWHM of 69.8nm soft-X-ray laser under different plasma lengths conditions also has been calculated taking advantage of pulse width calculating theoretical model. In this model, the gain is approximately parabolic distribution taking into account the gain saturation effect. Those theoretical results provided basis for the analysis of experimental results.In experiment, first, the 46.9nm and 69.8nm lasing time comparative experiment has been carried out. Combined with the theoretical result obtained by snow plow model, it can be concluded that, the lasing time of 46.9nm laser is prior to the 69.8nm laser only about 1ns, both of them are occurred near the moment when the plasma column is compressed to the minimum radius. And with the growth of initial capillary Ar pressure, the internal dynamics pressure of plasma increase, the lasing time delay. Then, the FWHM of 69.8nm soft-X-ray laser under different plasma length and initial Ar gas pressure conditions are measured. Experiments show that the FWHM of 69.8nm soft-X-ray increase with the length of the gain medium augment when 69.8nm laser intensity reach gain saturation. It means that the laser pulse broaden when the laser saturation condition get deeper. On the other hand, before the 69.8nm soft-x-ray laser reach saturation, its FWHM is inversely proportional to the length of the gain medium.Lasing time and pulse width are the important parameters of temporal characteristics of soft-X-ray laser. The former reflects the gain generated time of corresponding level. The latter determine the the minimum time scale the laser pulse can distinguish. The temporal characteristics of soft-X-ray laser are decided by the state of plasma during Z-pinch process, because soft-X-ray laser is derived from amplification of spontaneous emission. Exploration of the temporal characteristics of the laser can help get deeper understand of the physical mechanisms of the formation of the soft-X-ray laser and the dynamical processing of Z-pinch effect. At the same time, the capillary discharge parameters can be optimized to meet the future applications of laser experiments by studying the change rule of pulse width under different experimental conditions.