CHARACTERIZATION OF THE HELICAL UNDULATOR HELIOS-I IN THE 520 TO 930 EV RANGE USING A MULTILAYER POLARIMETER

A W/Si multilayer was used to determine the degree of circular polariz ation of the soft x-ray radiation of the European Synchrotron Radiatio n Facility helical undulator HELIOS I. The multilayer, manufactured by vapor deposition serves as a wideband tunable polarization analyzer i n the photon energy range from 520 to 930 eV. The characterization of the multilayer's analyzing power, varying from 0.82 to 0.25 for these energies, indicates that it operates close to its calculated specifica tions. The lack of phase-shifters applicable in this energy range was overcome by a detailed analysis of the unpolarized background identifi ed as radiation from the magnetic lattice. In this way, the degree of circular polarization of HELIOS I was determined to exceed 0.85 for hv > 685 eV. (C) 1997 American Institute of Physics.