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Beamline Description

The beamline


The optical layout of the BEAR beam line is based on the PMGM (Plane Mirror Plane Grating) configuration [see G. Naletto et al., Pure Applied Optics 1, 357, 1992]. Any movement of the beam is monitored by a photon beam position monitor (BPM) installed at the beginning of the beamline. After this, the beamline is equipped with a device for selecting the polarization of light. The PMGM configuration is based mainly on a first parabolic mirror, collimating the light emitted by the BM source without any entrance slit, a monochromator working in parallel light at variable deviation angle, a second parabolic mirror focusing the dispersed beam onto the exit slit, and finally an elliptical mirror focussing the beam on the sample. The layout has been conceived to be theoretically aberration free and to have the non plane optics in sagittal focusing. This configuration reduces the slope error aberration effects on the dispersion plane of a factor 1/cos. The polarisation effects introduced by the sagittal focusing of the non plane optics are compensated by the tangential focusing of the monochromator plane optics. The bending magnet light is collimated on the monochromator by a platinum coated mirror, working in sagittal focusing. The mirror is placed at 12059 mm from the source. Eventual movements of the source are monitored by a Photon Beam Position Monitor. The monochromator is based on two different channels working in parallel light: the grazing incidence channel working in the 40-1600 eV energy range, and the normal incidence channel working in the 3-50 eV energy range. Both channels are mounted on the same mechanical stage, whose horizontal translation allows to select the different channel. A second paraboloidal mirror P2 collects the radiation coming from the monochromator focusing it onto the exit slits. The monochromatized beam is focused into the exit slits. The beam is focused on the sample by an ellipsoidal mirror (REFO). The intensity of the light on the sample is monitored on the monitor section.


Layout of the BEAR beamline


 

Last Updated on Thursday, 12 October 2017 18:25