Commissioning results and performance of the high-resolution Russian–German Beamline at BESSY II

Excellent results were obtained during commissioning of the Russian–German Beamline at bending-magnet D16-1A of the electron-storage ring BESSY II. The beamline is based on a Petersen-type plane-grating monochromator covering the XUV and soft X-ray photon-energy range. Photoionization spectra taken from the 2,–13 resonance of doubly excited He reveal a resolving power of E/ΔE≅100,000 at hν=64.12 eV. To our knowledge, this represents the best energy resolution achieved up to now on a bending-magnet beamline in the grazing-incidence photon-energy range. We present results on photon flux and dimensions of the light spot at the sample position, and show representative photoionization spectra of several gases studied in the course of the characterization of the beamline at various photon energies. The high stability of the beamline is demonstrated by the first observation of the weak 4,−24 resonance of doubly excited He, which had not been observed before.