FIXED EXIT DOUBLE-CRYSTAL MONOCHROMATOR WITH ONE SINGLE COOLED CRYSTAL

The performance of a fixed exit double-crystal monochromator in terms of stability and reproducibility of the outgoing X-ray beam becomes th e crucial point at modern synchrotron beamlines dealing with high-reso lution X-ray optics. Due to the high heat load the monochromator cryst als have to be cryogenically cooled. The cooling loop of the second cr ystal may have an impact on the performance of the monochromator. We t herefore suggest to use a Si1-xGex single crystal as the first cooled crystal of the monochromator. The second crystal is held at room tempe rature. To verify the proposed solution an experiment was performed wh ere the lattice parameters of pure Si and SiGe crystals as a function of the temperature were measured. (C) 1998 Published by Elsevier Scien ce B.V. All lights reserved.