A High Precision Priest Interferometer

Abstract

A novel Priest-type interferometer has been built to measure small differences in expansion of fused silica. The interferometer block consists of a 3-cm. diameter cylinder, 10 cm in height, wrung onto a shorter cylinder. The sample is supported in a 0.64-cm off-axis hole. Two 5-µm diameter silica fibers and the upper curved surface of the sample provide three point contact with the semi-circular upper flat. Temperature control is accomplished by circulating fluid from a constant temperature bath through the walls of a double-walled chamber. The fringe separation is measured with an automatic counter. The apparatus is appropriate for measuring the expansion of any material having an expansion close to that of fused silica. Absolute expansions can be measured by appropriate calibration of the interferometer using specimens of known expansion.