Filamentary Transition and Energy Stability Optimization of High Pressure Nanosecond Pulsed Discharges for Laser Chambers

The diatomic rare gas halide excimer laser is currently the mainstream excimer laser, featuring short wavelength and high power. Experimental observations have shown that the cathode of the laser exhibits localized filamentation phenomena along the longitudinal length, which affects the laser gain. In this study, we utilized the PASSKEy2 code to develop a 0-2D coupled model for ArF excimer lasers, where the glow region was calculated using a OD kinetic model and the filamentary phase was calculated using a 2D fluid model. Meanwhile, a coupled pulse magnetic compression circuit was used to self-consistently calculate the cathode voltage, and the results matched well with experimental data. During the simulation, it was found that by adding a local deformation of about 10 um on the cathode surface to simulate the cathode hotspot, the discharge generated filaments from the cathode hotspot and gradually propagated towards the anode, forming a high-density filamentary channel with a diameter of about 0.6 mm. As the area of filamentary region increased, the energy deposited in the uniform glow phase under single pulse gradually decreased. Due to the strong electric field caused by the cathode hotspot, the filamentary phase would reach the ionization threshold and current peak faster, resulting in the electrode voltage being pulled down rapidly, which ultimately leading to the early termination of the glow discharge. In this process, the difference in total discharge current was not significant, but there was a substantial difference in energy distribution between the filamentary and glow phases. Adjusting the parameters of the magnetic compression circuit can enhance the efficiency of energy distribution in the glow phase.