Comparative monochromator studies for a soft x-ray microfocus beamline forBESSY-II

We present a comparative study for a microfocus beamline at the U41 undulat or, the most brilliant source at BESSY-II, High flux and an illuminated sam ple spot size between I and 10 mu m are the primary design goals to bridge the spatial resolution gap attainable with imaging photoelectron emission m icroscopy and microspectroscopy applications. The basic layout of the beaml ine consists of a monochromatisation and a subsequent refocusing stage. For the former, a focused spherical grating monochromator (FSGM) design and a collimated plane grating monochromator (PGM) were optimised. Both monochrom ator make use of the same refocusing stage: For limited spatial resolution but large working distance between the last mirror chamber and focal spot, a horizontal deflecting toroid will give a spot of 10x20 mu m(2). The secon d system, a Kirkpatrick-Baez arrangement of bent plane-elliptical mirrors i s expected to reach a 1 x 1 mu m(2) spot. The plane grating monochromator w as finally chosen for its high flux and versatility. Ray trace calculations indicate a photon flux of ca. 3x10(13) photons/s at a spectral resolution E/Delta E above 2300. (C) 1999 Elsevier Science B.V. All rights reserved.