Elliptically polarizing undulator beamline 4.0.1 for magnetic spectroscopy at the advanced light source.

A beamline for high resolution spectroscopy with elliptically polarized X-rays is described. The working energy range is large, from 20 eV to above 1800 eV. The resolving power is on the order of 10,000 at low energies (20 eV- 200 eV) and 6000 at high energies (200 eV-1800 eV). This is achieved using a variable deviation angle plane grating monochromator. A single grating;, with one line density and a varying groove depth, is used to cover the entire energy range. The beamline has been designed to operate with either one or two x-ray beams propagating simultaneously through the monochromator and to the experimental station. Switching between polarizations at rates of 0.1 Hz and slower is accomplished in the single beam mode by alternating the output of the elliptically polarized undulator source between left and right polarization. Fast polarization switching, at rates of 100-1000 Hz, is provided in the two beam mode by mechanical chopping between two photon beams, one of which is right circularly polarized, and the other left circularly polarized.