Three exit beams from a single (hkl) X-ray diffraction plane

An unusual case of three diffracted beams from a single incoming monochromatic X-ray beam and from the same Bragg plane is reported. Extremely asymmetric diffraction in a thin Si perfect crystal with a cleaved lateral face was experimentally studied. Two of the beams emerge grazing the front and back faces and the third beam emerges from the lateral face.