Characteristics of Double-Pulse Discharge in Supersonic Flow for Excimer Laser Excitation

Abstract

The development of a high-repetition-rate excimer laser is a vital requirement for providing a high average power and a high throughput. However, its development has been limited by various factors produced by excitation discharge. In this study, a double-pulse discharge method in a supersonic flow with a Mach number of 2.0 is used to simulate a high-repetition-rate excimer laser. An equivalent repetition rate f for the stable discharge of as high as 17 kHz is obtained. A glow discharge is also obtained between the electrodes at f ¼ 20 kHz; however, a discharge between the cathode and the UV pins appears almost simultaneously. At f ! 25 kHz, the second discharge becomes an arc through the heated column produced by the former discharge or in the region downstream of the shock wave moving upstream from the heated column. It is clearly demonstrated in this study that not only the heated column but also the shock wave has a key effect on the stability of the subsequent discharge. From the results, a formula for estimating the maximum repetition rate in a supersonic flow is proposed.