Total spectral radiant flux measurements on Xe excimer lamps from 115 nm to 1000 nm

Xe excimer lamps are used as VUV source for industrial application like surface cleaning. To determine the VUV efficiency of the lamp the radiant flux need to be known. Due to the difficulties of VUV measurements, it is often determined by interpolation from a value of a fixed angle, which results in large uncertainties. Here a goniometric setup is presented to measure the radiant flux of VUV sources like Xe excimer lamps which emit a narrow spectral band in the VUV range between X = 147 nm and 200 nm with a peak at 172 nm and spectral lines in NIR. By the use of two monochromators, we measure the spectral resolved radiant flux from 120 nm to 1000 nm. The measurement uncertainty of 9.7% is rather low for the VUV spectral range and depends mainly on the uncertainty of the used deuterium calibration standard from PTB (7%). Due to the strong temperature dependence of the transmission edge of silica used for the lamp vessel, the measurements are done in nitrogen atmosphere to ensure the convection cooling of the lamp. We measured the radiance distribution curve and radiant flux of Xe excimer lamps and could show the angle dependence of the spectrum. The measured correlation between the VUV band and the NIR lines gives us a better understanding of the plasma kinetics, which is used to optimize the pulsed excitation of the lamp.