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Electrical Engineering, Measurement and Control Technology
A beamline for advanced dichroism (BACH), to perform light polarization dependent experiments in the 35–1600 eV photon energy range is under construction at the ELETTRA Synchrotron Radiation Source in Trieste, Italy. The radiation source, based on two APPLE-II helical undulators, is designed for high photon flux and high resolving powers. The photons dispersion system is based on a Padmore variable angle spherical grating monochromator with a typical resolving power of 20 000–6000, 20 000–6000, and 15 000–5000 in the energy ranges 35–200 eV, 200–500 eV, and 500–1600 eV, respectively. Two separate branches after the monochromator allow setting two independent experimental chambers. The photon flux in the experimental chamber(s), calculated at the best resolutions achievable and with the aperture of the slits set at 10 μm, is expected to be above 1011 photons's with linearly or circularly polarized light. In addition, a fourth grating operates in the 400–1600 eV range to provide a higher flux, 1012 photons's with smaller resolving power (10 000–2000), allowing fluorescence and x-ray scattering experiments. The refocusing section(s), based on plane elliptical mirrors in a Kirkpatrick–Baez scheme, will provide on the sample, a nearly free-aberration spot(s), whose dimensions are expected to be 200×10 μm2 (horizontal×vertical). In the following, the general layout of the beamline is reported and the characteristics of the optical elements, as well as the optical performances (resolving powers and efficiencies of the monochromator, flux, and spot dimensions) are described in detail. © 2001 American Institute of Physics.
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