Laser interferometer for high temperature isothermal length changes over long time periods

Abstract

A laser interferometer for high precision isothermal length change measurements over long periods of time at high temperatures is described. An example is presented of the length change of a solid material near 500 K measured over several hours. The operating range of the device is from ambient temperature to 900 K, with an ultimate length change resolution of 10 nm. The critical optical alignment of the interferometer is performed and maintained by a minicomputer using an auto-alignment control feature. Particular emphasis has been placed on long term system stability (measurement time scales greater than a few minutes) for studies of the high temperature isothermal behavior of solid materials as a function of time. To account for small temperature fluctuations in these measurements, a technique is presented for correction of the results for sample length changes induced by thermal expansion.