High-current discharge pumping of ArF, F 2 lasers without cathode hot spots and filament instabilities

The aim of this work is spectroscopic diagnostics of a discharge in a new compact 'sealed-off' excimer laser. Spatial-time behaviors of the main excited atomic and ionic species, gas temperature and electron density were monitored with ns-gated ICCD camera from spontaneous emission spectra of the discharge. Ignition of cathode hot spots is detected from atomic emission lines of a cathode material. At increased current density cathode hot spots appear after the end of the pumping pulse because of delayed explosion of overheated emission centers on the cathode surface. No constrictions have been developed in the discharge from these spots because the pumping is very short. At highest pulse repetition rate discharge constriction is initiated from accumulated overheating of the boundary gas layer near the cathode surface.