Gas‐Monitor Detector for Intense and Pulsed VUV/EUV Free‐Electron Laser Radiation

In the framework of current developments of new powerful VUV and EUV radiation sources, like VUV free‐electron‐lasers or EUV plasma sources for 13‐nm lithography, we developed a gas‐monitor detector in order to measure the photon flux of highly intense and extremely pulsed VUV and EUV radiation in absolute terms. The device is based on atomic photoionization of a rare gas at low particle density. Therefore, it is free of degradation and almost transparent, which allows the detector to be used as a continuously working beam‐intensity monitor. The extended dynamic range of the detector allowed its calibration with relative standard uncertainties of 4% in the Radiometry Laboratory of the Physikalisch‐Technische Bundesanstalt at the electron‐storage ring BESSY II in Berlin using spectrally dispersed synchrotron radiation at low photon intensities and its utilization for absolute photon flux measurements of high power sources. In the present contribution, we describe the design of the detector and its applicat...