Observation of excitation discharge on an excimer laser in nonuniform gas density distribution

In excimer lasers, the excitation discharge causes various instabilities in subsequent discharge which collapse the highly-repetitive operation. The present study has investigated the effects of the gas density depletion on the excitation discharge instability eliminating the shock waves, the residual ions and the discharge products. The gas density depletion is simulated by utilizing a subsonic flow between the curve electrodes. We have compared the discharge that occurred in the gas density depletion with that by the double- pulse experiment in the stable gas. The gas density distribution is observed by using a Mach-Zehnder interferometer combined with a high-speed image-converter camera. We have found that the big density non-uniformity tends to cause the arc without the shocks, ions and products. The transition from glow to arc with respect to the gas density depletion occurs almost discontinuously. On the other hand, the second discharge on the double-pulse discharge becomes arc in much smaller non-uniformity, where the transition occurs very slowly. Therefore, it can be suggested that the discharge instability is also caused by some factors other than gas density depletion.