Oliver Rosier

The efficiency of coaxial KrCl* excilamps

The spectrum, input power and 222 nm radiant efficiency were measured for coaxial KrCl* excilamps based on a dielectric barrier discharge. The inner tubes of the lamps have an inner/outer diameter (ID/OD) of 14/16 mm. The OD of the outer tubes is 40 mm with wall thicknesses of 1.2, 1.5 or 2.0 mm. The lamps were driven by sinusoidal, rectangular and pulsed electronic control gears (ECGs). The 222 nm radiant power is derived from irradiance, according to the Keitz formula. The input electric power is measured with an oscilloscope, combined with a voltage probe and a current probe. The results show that the maximum efficiency of the 222 nm radiation is 9.2% for a KrCl* excilamp with a wall thickness of 1.2 mm, filled with krypton (198 mbar) and chlorine (2 mbar), driven by a pulsed ECG. The effects of waveform, frequency, wall temperature and transmittance of the tube are discussed. We observe that the filament configuration of the micro-discharges changes for different voltage waveforms. The results of gas composition and pressure show an optimum pressure at 200 mbar and an optimum chlorine percentage around 0.4–1.0%.