<title>Numerical simulation of shock waves in cavity of excimer laser</title>

ABSTRACT To clarify the characteristics of the generation and propagation of shock waves generated by pulse dischargesin an excimer laser, numerical simulation using a TVD scheme and a grid-distortion splitting method is carriedout. The calculations are condueted in conditions corresponding to our visualization experiments and high-frequencyoperations. The propagation and attenuation of the shock waves in the high-frequency operation are visualized fromthe numerical results.Keywords: shock waves, numerical simulation, excimer laser, flow visualization, color schlieren technique 1. INTRODUCTION Shock waves are generated by pulse discharges in the cavity of an excimer laser. Such waves break the homogeneous distribution of gas properties in the discharge region of the excimer laser, and cause arcing in the successive dischargesand inhomogenous excitation of laser gas in a high-frequency operation. Shock waves caused by the periodic pulsedischarges compel us to limit the frequency' in high power excimer laser operation. This paper clarifies the behaviorof the shock waves in an excimer laser cavity numerically. Prior to the numerical simulation, in order to obtainimages of these shock waves in experiments, we developed an excimer laser chamber with optical windows. By usingthis apparatus and a CCD schlieren technique, the horizontally propagating shock waves from the main dischargeregion, the shock waves from sparking pin gaps, and those from the surfaces of the main electrodes were observed withtheir characteristic properties24. To clarify the generation and propagation of these shock waves, two-dimensionalnumerical calculations using a TVD scheme57 and a grid-distortion splitting method2 are carried out in conditions