Measurement of radiation and temperature of cathode spots in excimer laser discharge

Abstract

Cathode spots and streamer discharges in excimer laser discharges shorten the life of electrodes because they cause the current concentration. One of the problems to develop a long-lived excimer laser is to remove cathode spots and streamer discharges in excimer laser discharges. In this paper, we measured the radiation timing of cathode spats and streamer discharges, and estimated the temperature of cathode spots and glow discharges by analyzing the spectra. The following results were obtained from the measurements. Cathode spots begin to radiate at about 20 ns after the discharge initiation, and the radiation peaks appear at the first zero point and approximately at the second zero point of the discharge current. Streamer discharges develop rapidly between the anode and the cathode at the second radiation peak of cathode spots, while glow discharges diminish and almost disappear at this period. The temperature of the cathode spats and the glow discharges are about 5500K and 2600K, respectively. They are constant in a charging voltage range from 13kV to 19kV. On the other hand, the average discharge temperature, which is found to be 2700K below the charging voltage of 17kV, increases above 17kV and reaches 3300K at 19kV. From these results, we conclude that the charging voltage for the excimer laser used in this work should be kept below 17kV in order to extend the laser lifetime.