A High Precision Laser Assisted X-Ray Goniometer for Circular Plates.

An X-ray goniometer system capable of high accuracy measurements on thin, circular crystal plates is described. The errors in previous systems have been due primarily to the fact that, whereas one wishes to measure the angle between the atomic plane and the plate face, goniometers in general measure the angle between the atomic plane and a plane defined by the goniometer which is not necessarily parallel to the plate face. The system described corrects for the inaccuracies associated with the goniometer by means of a laser alignment system. The X-ray beam and a laser beam are reflected from the same point on the plate. The reflected laser beam is monitored with position sensing photodetectors which can detect the position of the plate face with accuracies better than 0.5 seconds of arc. The accuracy of measurements is thus limited primarily by the accuracy with which the peak of the X-ray rocking curve can be determined. A prototype of the measurement system has been assembled from commercially available components.