A SELF-CONSISTENT MODEL FOR THE DISCHARGE KINETICS IN A HIGH-REPETITION-RATE COPPER-VAPOR LASER

A self-consistent computer model has been developed to simulate the di scharge kinetics and lasing characteristics of a copper-vapor laser (C VL) for typical operating conditions. Using a detailed rate-equation a nalysis, the model calculates the spatio-temporal evolution of the pop ulation densities of 11 atomic and ionic copper levels, four neon leve ls, and includes 70 collisional and radiative processes, in addition t o radial particle transport. The long-term evolution of the plasma is taken into account by integrating the set of coupled rate equations de scribing the discharge and electrical circuit through multiple excitat ion-afterglow cycles. A time-dependent two-electron group model, based on a bi-Maxwellian electron energy distribution function, has been us ed to evaluate the energy partitioning between the copper vapor and th e neon-buffer gas. The behavior of the plasma in the cooler end region s of the discharge tube near the electrodes, where the plasma kinetics are dominated by the buffer gas, has also been modeled. Results from the model have been compared to experimental data for a narrow-bore (p hi = 1.8 cm) CVL operating under optimum conditions. Close agreement i s obtained between the results from the model and experimental data wh en comparing electrical I-V characteristics of the discharge tube and circuit, and spatio-temporal evolution of the population densities of the laser levels and other excited Cu I and Ne I states, and lasing ch aracteristics. During the period of lasing action, the populations of the laser levels are perturbed by 10-20 percent due to stimulated emis sion. During the excitation phase, a significant population resides in the Cu I quadruplet states and in the Cu+ metastable ion level. Depl etion of electrons in the high-energy tail (epsilon > 16.7 eV) of the electron energy distribution function is found to occur during the exc itation phase, resulting in weak excitation of the neon-buffer gas in the central zone containing the Cu-Ne mixture. For the neon plasma in the end zones near the electrodes, the population densities of the neo n excited states and ions are typically two orders of magnitude higher than in the central zone.