A detector system based on the photoionization of rare gases at low particle densities has been developed for absolute photon flux measurements of highly intense and extremely pulsed radiation in the VUV and EUV spectral range. Due to its wide dynamic range, the device can be calibrated with spectrally dispersed synchrotron radiation at low photon intensities but applied with high power sources. The detector is free of degradation and almost transparent, and therefore suitable for intensity monitoring. We describe here the application of the detector for flux measurements at a beamline for undispersed deflected undulator radiation in the PTB Radiometry Laboratory at the electron storage ring BESSY II. In the single-bunch operation mode of BESSY II, measurements of the pulse energy down to 3 nJ for single EUV pulses have been performed. This demonstrates the capability of the gas detector for a broad range of applications with pulsed EUV sources.