X-RAY OPTICS IN METROLOGICAL APPLICATIONS

Highly pure silicon crystals with an almost perfect lattice structure constitute a powerful metrological tool. In real Si-crystals lattice spacings with an accuracy better than 1 part in 107 are realized. These have been applied as length standards in the sub-nanometer region using the scanning X-ray interferometer, and as angle standards in the nanorad region with angle X-ray interferometers. Crystallographic angles between different sets of lattice planes within the same crystal differ only slightly (1 × 10-9 rad) from values calculated for the perfect crystal. In a double-crystal arrangement Si-crystals have been used as a single-crystal polygon in order to calibrate optical angle encoders.