Avalanche discharge pumped xenon-chloride lasers in high pressure and high current density regimes

The central theme of this thesis addresses issues related to the high pressure performance of an important member of Rare-gas Halide (RGH) excimer lasers, the XeCl B{dollar}rightarrow{dollar}X laser, under intense discharge pumping. The potential of the broad-band XeCl C{dollar}rightarrow{dollar}A and XeF C{dollar}rightarrow{dollar}A transitions as possible tunable discharge lasers are also assessed experimentally (reported in Appendices A & B).; To carry out experiments at high gas pressures (up to 20 atm), we make use of an x-ray preionized, cable driven small discharge chamber active volume (4 x 0.5 x 1cm{dollar}sp3{dollar}) (CSDC). For the experiments under conditions of very high discharge current, a low impedance (0.4 {dollar}Omega{dollar}) water transmission-line driven discharge device (WTLDD) is employed.; Most recently, preliminary exploration of the very high discharge current regimes (up to j = 16 kA/cm{dollar}sp2{dollar}), high net gain (G = 0.63/cm) and high power laser action ({dollar}sim{dollar}3.1MW) performed in collaboration with J. G. Xie are observed in a 14 x 0.3 x 0.9 cm{dollar}sp3{dollar} volume discharge. The temporal behaviour of the XeCl B{dollar}rightarrow{dollar}X fluorescence exhibits a distinct double pulse structure. As suggested by Professor S. C. Lin, this double pulse time behaviour of the XeCl B{dollar}rightarrow{dollar}X fluorescence may indicate the presence of two important XeCl (B,C) formation processes. The short first pulse can be attributed to the rapid ionic recombination process, whereas the long second pulse could be a three body harpooning reaction: Xe{dollar}sp*{dollar} + Cl + Ne {dollar}rightarrow{dollar} XeCl (B or C) + Ne.; As indicated by measurements of discharge voltage waveforms, sufficiently high level of preionization electron can reduce the avalanche formation time t{dollar}sb{lcub}rm A{rcub}{dollar}. This effect is most evident in discharges under marginal E/n breakdown conditions. An analytical two stage model gives predictions which are in reasonable agreement with experimental results. We also demonstrated that preionization remains effective up to 20 {dollar}mu{dollar}s in typical XeCl laser gas mixtures for a 100 ns preionization pulse. Such a long preionization delay time can only be attributed to the long survival time of the low energy electrons in XeCl laser mixtures. We subsequently concluded that at high gas pressures, the principal loss channels for the electrons are 2- and 3- body electron-ionic dimer dissociative recombinations.