MODELING OF THE KINETICS AND PARAMETRIC BEHAVIOR OF A COPPER-VAPOR LASER - OUTPUT POWER LIMITATION ISSUES

A self-consistent computer model was used to simulate the plasma kinet ics (radially resolved) and parametric behaviour of an 18 mm bore (6 W ) copper vapour laser for a wide range of optimum and non-optimum oper ating conditions. Good quantitative agreement was obtained between mod elled results and experimental data including the temporal evolution o f the 4p(2) P-3/2, 4s(2) D-2(5/2) and 4s(2) D-2(3/2) Cu laser level po pulations derived from hook method measurements. The modelled results show that the two most important parameters that affect laser behaviou r are the ground state copper density and the peak electron temperatur e T-e. For a given pulse repetition frequency (prf), maximum laser pow er is achieved by matching the copper atom density to the input pulse energy thereby maintaining the peak T-e at around 3 eV. However, there is a threshold wall temperature (and copper density) above which the plasma tube becomes thermally unstable. At low prf (<8 kHz), this ther mal instability limits the attainable copper density (and consequently the laser output power) to values below the optimum for matching to t he input pulse energy. For higher prf values (>8 kHz), the copper dens ity can be matched to the input pulse energy to give maximum laser pow er because the corresponding wall temperature then falls below the thr eshold temperature for thermal instability. For prf >14 kHz, the laser output becomes highly annular across the tube diameter due to a sever e depletion of the copper atom density on axis caused by radial ion pu mping. (C) 1997 American Institute of Physics.