| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 93 === In the past few years, there has been considerable interest in using small-scale, high power, femtosecond laser system operating at high repetition rates to generate optical-field-ionization(OFI) plasmas suitable as gain media for collisional excited lasers at xuv wavelengths (< 50 nm). Saturation amplification has been reported by using gas cell targets. In addition, the further development of driving such xuv lasers in plasma waveguides have revealed its potential.
The first chapter of this thesis presents the historic review of xray lasers and the first demonstration of an optical-field-ionization (OFI) x-ray laser with a laser-irradiated xenon clustered gas jet. Near saturated amplification was achieved. The output energy reached 95 nJ, and the divergence angle of which was 5.2 mrad. In comparison with previous OFI x-ray lasers which use gas cell targets, the use of gas jet make contamination-free and long-term operation possible. For xuv lasers of such class, the lifetime of the population inversion is short and so the pumping must be in the form of a traveling wave. This can be achieved most easily by longitudinal pumping. The most serious issue by longitudinal pumping is the formation of a sufficient length of plasma for amplification of xray photons. In order to extend the gain length, it is necessary to guide the pump pulse over many Rayleigh lengths.
In the second chapter, by using the axicon ignitor-heater scheme on a 5-mm slit jet, we successively generated high quality plasma waveguides with significantly improved efficiency of guiding laser pulses with peak intensities relevant to OFI schemes.
The result of a preliminary experiment for OFI x-ray lasers driven in a plasma waveguide is reported and analyzed in the third chapter. Finally, such plasma waveguide will be applied on different ion species to push the OFI lsers toward shorter wavelength and saturation.
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