A Computer Controlled Interferometer System for Precision Relative Angle Measurements

Abstract

An angle measuring interferometer system has been constructed for use in a high precision crystal‐diffraction γ‐ and x‐ray spectrometer. The angle measuring device has been designed to be free of most sources of systematic error (e.g., movements of the axes of rotation, thermal effects, etc.). Electronic circuits count ¼‐fringe increments which correspond to a change in angle between two rotating platforms of Δφ=0.025″. A PDP‐8 computer reads the incremental fringe count and corrects drifts in angle by applying analog signals to magnetostrictive transducers. Using the computer, the spectrometer can be made to scan over a succession of diffraction angles, remaining locked at each position under feedback control. Preliminary tests indicate that the over‐all system is capable of making consistent diffraction‐angle measurements within an accuracy of ±0.005″; this upper limit of stability is determined by the spectrometer resolution and the limited counting statistics obtained.