'Billet and Meslin bi-lenses' in two-beam X-ray interferometry

The problem of the interference patterns of X-ray interferometers, when the primary beam is a monochromatic X-ray radiation from point sources is discussed. In this case the diffraction of the beam for vacuum propagation is discussed. X-ray two-beam interferometer with narrow interplane thicknesses, three-block defocused and three-block different thickness systems are used. The analogue is shown of the first two interferometers with the known 'Billet bi-lens' system and of the third one with the 'Meslin bi-lens' system. (author)