Laterally-graded Si1-xGex crystals for high resolution synchrotron x-ray optics.

We present first experimental data on a novel type of optical element for synchrotron radiation applications in the x-ray region: namely laterally-graded aperiodic crystals on the basis of Si1-XGeX alloys. The lattice parameter of such a gradient crystal containing up to some atomic % Ge in a Si single crystal changes nearly linearly along the plane of diffraction. Thus the variation of the Bragg angle of divergent incident light on the crystal can be compensated for. This opens up the possibility to operate a crystal monochromator in nearly crystal limited resolution in the whole energy range above 2 keV at the full vertical divergence without a collimating premirror. Simultaneously the reflected spectral intensity can be increased considerably as compared with a conventional Si-crystal monochromator.