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Visualization of Double-Pulse Discharge in Excimer Laser with Gas Flow

The double-pulse discharge has been demonstrated in a gas flow with a velocity of 200 m/s which is generated by a Ludwieg tube. A gas mixture of helium and argon is used to simulate the excitation discharge of excimer lasers. The shock waves and the gas density perturbation between two successive discharges have also been visualized applying the shadowgraph technique using a high-speed image-converter camera. The second discharge at an equivalent pulse repetition frequency (f) of 10 kHz becomes an arc through the heated column which is generated by the first discharge. At f=5 kHz, the glow discharge can be produced between the electrodes, however, an arc is also observed through the heated column which is located somewhat downstream of the electrodes. Only a glow discharge is possible up to f=3 kHz. These results clearly demonstrate that the heated column has a decisive effect on the stability of repetitive pulse discharges.