Applications of high-order Laue-case rocking curves

Spherical-wave Pendellösung fringes have been used for many years to make absolute measurements of X-ray coherent scattering amplitudes. Bonse & Teworte [J. Appl. Cryst. (1980), 13, 410-416] have suggested that the corresponding fringes seen in Laue-case rocking curves between two crystals with almost equal thicknesses might have important applications and they showed that agreement to within ½% could be achieved in structure factor measurements on silicon. Two further applications are demonstrated in this paper. By a simple construction the range of double-crystal topography, using only a Lang camera, has been extended to the region δd/d < 10-9. In another experiment it is found that the Pendellösung method can be extended to very high orders (the 10,10,0 reflection in silicon for example) so that attention can be focused, for the first time with high precision, on the coherent Bragg scattering at very high sin θ/λ.