THE RESOLUTION FUNCTION OF A TRIPLE-CRYSTAL DIFFRACTOMETER FOR HIGH-ENERGY SYNCHROTRON-RADIATION .2. DISPERSIVE LAUE GEOMETRY

The k-space resolution function of a new triple-crystal diffractometer for high-energy synchrotron radiation is calculated for an arrangemen t of three perfect silicon crystals diffracting in dispersive Laue geo metry. A comparison is made with the results of measurements using 100 keV synchrotron radiation. The settings (<(2) over bar ><(2) over bar 0>, 111, (2) over bar<(2)over bar 0>) and ((2) over bar<(2)over bar 0 >, 400, (2) over bar<(2)over bar 0>) are discussed in detail. All feat ures of the measured resolution function are well reproduced by the ca lculations, especially if the background due to non-Bragg scattering f rom the collimators and the crystals is taken into account. In additio n, approximate formulas are presented that provide a quick survey over the features of the resolution in k space for a given experimental se t-up. On the 50% contour level, the lambda streak is by far the domina ting feature of the resolution function and reduces the resolution par allel to G(sample) by a factor of 40 to about 8 x 10(-3) Angstrom(-1). The excellent resolution in the scattering plane perpendicular to G(s ample) of 10(-5) Angstrom(-1) is not affected. Unlike in the nondisper sive case and diffraction experiments using characteristic lines of X- ray tubes, here the location and the intensity distribution of the mon ochromator streak depend on the Bragg angles of the monochromator, sam ple and analyzer crystal.