A beamline for time resolved photoelectron microscopy on magnetic materials at the Swiss light source

We describe the "Surface/Interface: Microscopy" beamline currently under co nstruction at the Paul Scherrer Institut. This beamline will use a photoemi ssion electron microscope to study the electronic and magnetic structure of materials. Its photon energy range will be 94-2000 eV. To allow time resolved measurements with millisecond resolution we use a ne w scheme allowing to switch the photon helicity optically without perturbin g the electron orbit. Two identical elliptical insertion devices are placed behind each other in the same straight section. They can produce light wit h opposing helicities. These two sources are separated horizontally by intr oducing a small static parallel offset in the electron orbit. Switching bet ween the two rays of opposite helicities is done mechanically at the horizo ntal focus behind the monochromator. The two sources are brought to overlap on the sample by slightly defocussing the refocussing mirror. A commercial microscope (Deltax similar to 20 nm resolution) is adapted to the synchrotron by various upgrades. These include a software combining mic roscope and beamline control, a computer controlled mechanical alignment sy stem, a separate sample preparation chamber, and sample cooling using liqui d nitrogen. The beamline will be available for user operation in 2002. (C) 2001 Elsevier Science B.V. All rights reserved.