Intense excimer emission from pulsed microhollow cathode discharges

Abstract

Summary form only given, as follows. Direct current microhollow cathode discharges (MHCDs), operated in XeCl, ArF, Xe, Ar, Ne and He, are sources of excimer radiation with efficiencies between 1% and 10%. The radiant power of the excimer emission was found to increase linearly with current. For DC operation in xenon the current was kept below 8 mA, at a discharge voltage of 220 V, in order to avoid thermal damage of the electrodes. Reducing the average power by operating the discharge in a pulsed mode with on-times of 700 /spl mu/s and a duty cycle of 0.007 allowed us to increase the current to 70 mA, limited by the onset of instabilities. Whereas for this case the radiant power increased, as expected, by an order of magnitude over the dc values, the radiant emittance of the excimer source was found to stay constant due to the linear increase in the emitting plasma area with current For xenon, at a pressure of 760 Torr, it was measured as 2 W/cm/sup 2/. One possibility to increase the radiant emittance beyond this value, is to place MHCDs in series, as demonstrated with a XeCl tandem discharge. A second method of discharge operation, which provides not only an increase in radiant emittance, but also in radiant power is based on MHCD operation in a transient, nonequilibrium mode. By applying short voltage pulses, excimer emission pulses of 700 ns duration (FWHM) were generated with peak radiant power levels of six times the steady state levels. Using high speed VUV imaging system in combination with a calibrated radiometer, the peak radiant power density was measured as approximately 400 W/cm/sup 2/, more than two orders of magnitude above the dc value. Results of measurements on the recovery time of these pulsed excimer sources, indicate the possibility to generate repetitively pulsed, MHCD excimer emitters.