A high-resolution section topograph technique applicable to synchrotron radiation sources

Asymmetric Bragg reflection from the surface of a plane crystal monochromator is employed to provide the spatially narrow beam (width less than 10 μm) required for high resolution in X-ray section topographs. Details are given of apparatus in which the monochromator is traversed back and forth to even out local irregularities in its reflecting power, and a precisely positionable screen is interposed between the monochromator and specimen to cut out radiation reflected from imperfections below the monochromator surface. The system was designed to be tolerant of some imperfection in the monochromator and this objective was achieved. With Cu Kα₁ radiation, a natural diamond (111) face and the asymmetric 220 reflection, a lateral compression of the beam by a factor of 22.6 was obtained. Section topographs are exhibited in which the spatial width of the incident beam is only 7 μm. A benefit of this technique is the possibility of reducing the wavelength bandwidth effective in recording the topograph to less than that of the Kα₁ emission profile, and hence of reducing the contribution of dispersion to diffusion of the topograph image. The applicability of the method to synchrotron radiation sources is discussed.