Two-dimensional X-ray interferometry

This paper demonstrates the capability of X-ray interferometry for the measurement of the detailed parasitic motions that may occur in very high precision slideways. X-ray interferometry has been used for the first time to obtain simultaneous fringes by motion of the sensing crystal in two orthogonal directions, giving (with two independent X-ray sources) fringes corresponding respectively to the lattice spacings of (111) and (220) crystal planes. A monolithic X-ray interferometer was designed for this experiment, with two sets of leaf spring supports for the moving blade, so that it could be driven in the two orthogonal directions by magnet/coil transducers. A phase plate was positioned and moved so that three spatial-phase signals could be obtained for each positional measurement of each of the two axes, providing measurement accuracy of the order of 20 pm for the conditions of this experiment.