Beamline
Optical scheme of the beamline
The requirements for the source for the x-ray microscope, to preserve the central brightness and cut the incoherent part of the photon flux, are met by a modified version of a spherical grating monochromator (SGM) with a fixed entrance and exit slits.
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The SGM prefocusing system consists of a toroidal mirror performing a sagittal focusing of the beam into the entrance slit and tangential focusing into the exit slit. The plane mirror in combination with the grating allows the deflection angle at the grating to be changed in order to operate with minimal defocus aberration. The monochromator has two gratings with 600 and 1200 grooves/mm, which operate in outside diffraction order configuration with a deflection angle of 1740 and perform sagital focusing to the exit slit (see figure for the optical scheme of the beamline). A variable pinhole at the exit allows the beam to be tailored to the right conditions for illumination of the zone plates. According to the specification, the instrumental transmission should be of the order of 1% providing a resolution of 0.1 eV at the C K edge in a 30 µm exit slit. The tuning range covers photon energies from 250 to 1200 eV.
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