The new PTB beamlines for high-accuracy EUV reflectometry at BESSY II

High-accuracy characterization of optical components has been one of the main services of the PTB radiometry laboratory at BESSY I. Now, after the shut down of BESSY I with the end of 1999, PTB is operating two new beamlines suitable for EUV reflectometry at their new laboratory at BESSY II. As at BESSY I, synchrotron radiation from a bending magnet is used for reflectometry but additionally a beamline at an undulator covering the same spectral range from 50 eV to 1800 eV can be used for special applications where, e.g., high radiant power or very high spectral purity is needed. In this paper, the characteristics of the beamlines are presented. We present the results of the beamline characterization on photon flux, spectral resolution, spectral purity and beam stability with special respect to the EUV photon energy range. During the phase of simultaneous operation of BESSY I and II in 1999, a direct comparison was done for reflectance measurements at high quality Mo/Si EUV mirrors. The results showed perfect agreement: (68.98+/-0.17) % at BESSY I and (69.10+/-0.24) % at BESSY II. The wavelength scale was calibrated using the absorption resonances of Ar, Kr, and Xe whose energies are known with a relative uncertainty of about 10(-4). The measured peak positions agreed within this uncertainty.