| Since the first reported in 1984, soft X-ray laser as a coherent light source, characterized by good monochromaticity, high instant brightness, narrow pulse duration and short wavelength, seizes more and more scientists'attention. Soft X-ray laser could be generated through hitting solid targets with energetic and bulky laser, which requires high operating costs and in turn limits its application. Therefore, realizing the miniaturized, low running-cost soft X-ray laser has become the research focus of worldwide scientists.The proposal of capillary discharge is one of the most effective solutions to achieve desktop, miniaturized soft X-ray laser. Since 1994, the first time when Rocca and his colleagues in US successfully realized capillary discharge Ne-like Ar 46.9nm soft X-ray laser, there has been 7 other countries such as Japan and Italy, that succeed in achieving soft X-ray laser using the same mechanism, which significantly promotes the development of soft X-ray laser. Our research team realized 46.9nm soft X-ray laser output in 2004, using the experimental setup developed by ourself, and becomes the third research group in the world that claims saturation output of 46.9nm soft X-ray laser after several years'endeavor, and it is the first time to realize saturation output under both low current and low pressure condition in 2009. Realization of saturation under both low current and Ar pressure is avail the proposed of miniaturization, which pushes forward the development of soft X-ray laser both experimentally and theoretically to some extent. Saturation output under low main current means obtain the highest laser energy under low threshold, and low main current lead to low Ar pressure, which means small inverted population density, all of this will need the optimization of character. Centre on this theme, this thesis consists of three parts, i.e.: theoretical research, introduction and improvement of experimental instruments and experimental investigation, all of which serves for augmentation of laser energy and realization of stable output of saturated laser.Theoretically, chapter 2 analyzes systematically dependence of laser generation time on the initial Ar pressure and the amplitude of main pulse current, using numerical simulations in combination with experiments recur to the description of Z-pinch theory using Snow plow model. The theory presented in chapter 2 provides reference for determinations of discharge parameters during experiments. The fact that the existence of electron density gradient during plasma formation affects the transmission of soft X-ray laser, necessitates the detail investigation on light transmission within the plasma column under different electron densities by solving the light transmission equation. Finally, associated with the analysis of the shelter from pinhole and the experimental result of about 4mrad angle of divergence, the results prove that the electron density of plasma is approximately parabolic distribution. And the parabolic distribution of electron density is be propitious to the gain amplification when the laser transmitting through the plasma, in order to obtain higher laser energy.Capillary discharge device is mainly constituted of five parts, i.e.: main pulse system, prepulse system, detection system, working load and inflation as well as vacuum system. This thesis first describes the operation principle of main components for discharge device, and improvements of the device with regarded to enhancing the laser gain as well. The improved main switch can alter the rising edge of main pulse current through switching different inductors. The improved inflation system is conducive to investigate on the influence of gas mixture on laser gain. All in all, improvements of discharge device guarantee the reliability of operation of experiments.Chapter 4 describs experimental research in order to obtain higher gain. Firstly, the impact of the amplitude for main pulse current on laser gain was studied, the optimal amplitude was found when the given Ar pressure, and this is in favor of realizing higher gain coefficient. Secondly, the influence of mixture ratio of He with Ar on laser gain was studied, and the results show that the incorporation of a certain proportion of He will help to improve the laser gain, finally increase the laser output energy. This thesis also investigated the effect of main pulse rising edge on laser gain. Experiments indicate that the slow rising edge is conducive to produce higher laser gain, and accordingly improve the laser energy, providing that other conditions remain unchanged. Finally, we also analyzed the impact of amplitude for prepulse current on laser output under delay times of 2μs and 7μs between main pulse and prepulse, which serves to produce high laser gain and stable laser output. It is found that under an amplitude of 20A for prepulse current, laser tends to have the most stable output, and a relatively higher gain, and higher laser energy.In the aspect of the laser character and saturation research, firstly, monochromator was employed to analyze the time characteristics of laser. Apart from that, application of both flat-field grating spectrometer and Rowland spectrometer gives accurate spectroscopic information of capillary discharge soft X-ray laser, which confirms that the spike detected by X-ray diode is indeed Ne-like Ar 46.9nm soft X-ray laser. Secondly, the employment of slit-scan method shows that the spot diameters of 5.9mm and 6.1mm in the position of XRD, which corresponds to horizontal and vertical divergence angle of the laser were 4mrad and 4.1mrad respectively. The most important research of the thesis, by fitting with the Linford formula, gain coefficients under different discharge conditions were achieved. The maximum gain coefficient was 0.68cm-1. Gain coefficient of 0.5cm-1 was achieved under both low current and low pressure condition, which is the first time realization in the world. The laser energy was estimated to be 67.4μJ through calibrating the X-ray diode. Finally, the thesis discussed the possibility of reaching shorter wavelength laser using mechanism of capillary discharge.
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