| Summary: | 碩士 === 國立中正大學 === 物理系 === 91 === In this thesis, the history of x-ray laser developments is reviewed and the principle of x- ray laser generations and amplifications is discussed in details. The working theory and the function of the plasma and x-ray diagnostics employed in our experiments are also introduced. To reduce the refraction effect and increase the pumping laser energy absorbed in the laser-produced plasma, we design a multi-pulse pumping configuration to optimize the plasma condition for transient x-ray amplifications. By changing pumping pulse parameters such as pulse ratio and pulse delay between the pulses, we can control the electron density gradient, temperature and ionization state in the plasma. Besides, we develop a flat field spectrometer, a crystal spectrometer and a reflective shadowgraphy to measure and thus achieve the necessary plasma conditions for x-ray lasing gains. In our experiment, we successfully observe x-ray spectra generated from titanium target using the flat field spectrometer. We also measure the ionization balance of plasma by detecting the emission of the resonance line from highly ionized Ti ions. Furthermore we temporally resolve the onset of the ionization on targets caused by the pumping pulses using the reflective shadowgraphy. There are two possible lasing transition lines at 30.1 nm and 32.6 nm but with only low or no gain during our experiment. Our diagnostics suggest that the plasma temperature is too low to achieve high gain for x-ray amplifications due to a large preformed plasma produced by the undesired prepulse at 10 ns before the arrival of the main pulse. The main pulse does not have enough energy to heat up the preformed plasma. Further increasing the temporal contrast of the pumping laser system to avoid the pre-ionization on targets is necessary for achieving high temperature and high x-ray gain in the laser-produced plasma.
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