Performance of the Grating-Crystal Monochromator of the ALOISA beamline at the Elettra Synchrotron

he new beamline ALOISA, now operational at the Elettra Synchrotron, is designed for surface studies by means of several experimental techniques: surface x-ray diffraction and reflectivity, photoemission spectroscopy, photoelectron diffraction, e(-)-Auger coincidence spectroscopy. A new monochromator has been specifically designed and realized for this multipurpose beamline: it makes use of a channel-cut Si crystal dispersive element for the 3-8 keV range and of a plane mirror-plane grating element for the 200-2000 eV range. Both dispersive elements share the same optical system. In the low energy range (200-900 eV) the spectral resolving power exceeds 5000 while maintaining a throughput higher than 10(10) photons/s/200 mA/0.02% BW. In the case of the N-2 1s -->pi* and Ne 1s --> 3p transitions, the extremely high signal-to-noise ratio of the absorption spectra allowed a very accurate determination of the corresponding natural linewidth (116 +/- 2 and 250 +/- 10 eV, respectively). Moreover, the vibrational structure of the CO-oxygen 1s -->pi(*) transition has been fully resolved. In the high energy range, the measured flux exceeds 10(10) photons/s/200 mA up to 6.5 keV with a resolving power of similar to 7500.