Ballast free, large area microdischarge excimer lamps

Abstract

Summary form only given, as follows. By using a hollow cathode geometry, it is possible to generate stable, direct current high-pressure gas discharges even in electronegative gases. These discharges when either operated in noble gases or mixtures of noble gases and halogens have been proven to be very efficient sources of excimer radiation. For dc discharges in xenon, with typical sustaining voltages of 200 V, efficiencies of 6% to 9% have been measured. When operated with nanosecond pulses, efficiencies of up to 20% have been obtained. By limiting the area of the cathode around a microhole, it is possible to operate the microdischarge in an abnormal glow mode at moderate currents of milliamperes or less. In this mode, parallel operation of microhollow cathode discharges can be achieved without ballasting the individual discharges. Experiments with xenon as excimer gas have been performed, and the spatial distribution of the excimer emission from microdischarge arrays has been measured dependent on pressure and current. The dielectric layer was formed by means of plasma spraying. Various microhole patterns have been generated by using an excimer laser to drill sets of microholes with diameters of approximately 100 /spl mu/m, and to selectively eliminate the dielectric layer around these holes. With increasing current the microdicharges turn-on sequentially, and eventually the plasma fills the space between the holes and the dielectric, generating a homogeneous surface plasma source. One-dimensional (strings) as well as two-dimensional arrays with up to 100 microdischarges covering an area of 1 cm/sup 2/ have been studied. Since these devices can easily be scaled in size, microdischarge arrays can be used as large area surface emitters with excimer radiation intensities exceeding 1W/cm/sup 2/.