Performance of the grating-crystal monochromator of the ALOISA beamline at the Elettra Synchrotron

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Abstract
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

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