PGM beamline with constant energy resolution mode for U49-2 undulator at BESSY-II

A PGM beamline has been designed for the U49-2 undulator at BESSY-II in which the collimation by the preoptics is done in the dispersive and horizontal direction. The beamline is characterized by high flux, high brightness, high spectral resolution (E/ΔE>5000) over a wide spectral range of ∼70–1500 eV and a relatively small spot size of 70 μm×20 μm (fwhm). To achieve high spectral flux two interchangeable blazed gratings are used in the monochromator. For this beamline a new drive mode has been derived in which almost constant spectral resolution can be maintained while driving the monochromator on-blaze. This constant resolution is maintained even for gratings with different line densities.