We describe a bending magnet beamline designed to operate on a third generation synchrotron light source-the Advanced Light Source (ALS)-in the energy range 50-1300 eV. It was constructed for the characterization of optical elements (mirrors, gratings, multilayers, detectors, etc.) but has capabilities for a wide range of measurements in other fields, in particular materials science and atomic physics. The optical system consists of a monochromator, a reflectometer, a three-mirror order suppressor, and horizontal and vertical focusing mirrors to provide a small spot on the sample. The monochromator is a varied line spacing, plane grating (VLS-PGM) design in which the mechanically ruled grating operates in the converging light from a spherical minor working at high demagnification. The spherical aberration of this mirror is corrected by the grating line spacing variation, so that the monochromator is essentially aberration-free over its tuning range. Wavelength is scanned by simple rotation of the grating with a fixed exit slit. The small size and stability of the ALS source allows entrance slitless operation, leading to high flux and a spectral resolving power lambda/Delta lambda of around 7000, limited by the ALS vertical source size. The reflectometer has the capability of positioning the sample to 10 mu m and setting its angular position to 0.002 degrees. LABVIEW(TM)-based software provides a convenient interface to the user. The reflectometer is separated from the beamline by a differential pump, and can be pumped down to 10(-7) ton, in 0.5 h. This allows rapid turn-around of materials science samples for measurements which do not require UHV, such as NEXAFS. Auxiliary experimental stations can be mounted behind the reflectometer. Results are shown which demonstrate the performance and operational convenience of the beamline. (C) 1998 Published by Elsevier Science B.V. All rights reserved.
