Laterally-graded SiGe crystals for high resolution synchrotron optics

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 mixed crystal is presented. The lattice parameter of such gradient crystals containing up to some at. % Ge 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, 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 synchrotron source divergence without a collimating pre-mirror. Simultaneously the reflected spectral intensity can be increased considerably as compared with a conventional Si-crystal monochromator.