PERFORMANCE OF THE MODIFIED SX-700 PLANE GRATING MONOCHROMATOR AT THE FINNISH BEAMLINE IN MAX-LAB

A soft x-ray beamline designed principally for gas phase measurements has been constructed and tested at the 550-MeV MAX I electron storage ring in Lund, Sweden. The beamline uses synchrotron radiation from a short 35-period undulator with a magnetic period of 24 mm. The photon energy range of the undulator is about 60-600 eV covering, e.g., the important C, N and O 1s ionization regions. The beamline is based on a modified SX-700 plane grating monochromator with a plane elliptical focusing mirror. The beamline has been tested by measuring total ion and electron yield spectra from the rare gases Kr and Ar in the resonance excitation regions just below the Kr M4,5 and Ar L2,3 ionization thresholds. These results show that the monochromator has very high resolution, E/DELTAE almost-equal-to 4800 at 244 eV and almost-equal-to 7600 at 91 eV, comparable with the best spherical and plane grating monochromators. The beamline is equipped with an effective differential pumping system for the gas phase experiments combined with a refocusing mirror in order to provide a small spot size (phi < 1 mm) at the sample region.