The Resolution Function of a Triple-Crystal Diffractometer for High-Energy Synchrotron Radiation. II. Dispersive Laue Geometry

The k-space resolution function of a new triple-crystal diffractometer for high-energy synchrotron radiation is calculated for an arrangement of three perfect silicon crystals diffracting in dispersive Laue geometry. A comparison is made with the results of measurements using 100 keV synchrotron radiation. The settings (0, 111, 0) and (0, 400, 0) are discussed in detail. All features of the measured resolution function are well reproduced by the calculations, especially if the background due to non-Bragg scattering from the collimators and the crystals is taken into account. In addition, approximate formulas are presented that provide a quick survey over the features of the resolution in k space for a given experimental set-up. On the 50% contour level, the λ streak is by far the dominating feature of the resolution function and reduces the resolution parallel to G_sample by a factor of 40 to about 8 × 10⁻³ Å⁻¹. The excellent resolution in the scattering plane perpendicular to G_sample of 10⁻⁵ Å⁻¹ is not affected. Unlike in the nondispersive case and diffraction experiments using characteristic lines of X-ray tubes, here the location and the intensity distribution of the monochromator streak depend on the Bragg angles of the monochromator, sample and analyzer crystal.