Development of a Laser Interferometric Dilatometer

Abstract

The ongoing development of a high precision dilatometer using laser interferometry is described. Design criteria require operation over a temperature range from ambient to 900 K with a length change sensitivity of ten microinches (0.25 µm) or less. In addition, the dilatometer is designed to achieve rapid sample turnaround for quality control measurements in a production environment. To achieve this, design features are incorporated which minimize sample preparation time by relaxing critical size and shape restrictions on test samples. The length change measurement is based on a modified Michelson interferometer using a two-frequency HeNe laser and ac detection of fringes. The final critical alignment of the interferometer during sample installation is achieved by automatic computer control. This alignment control feature can be used to maximize interferometer alignment continuously through the course of a run. The furnace system incorporates a low thermal mass heating chamber to achieve rapid thermal response with minimal thermal disturbance to the interferometer system. Flexibility and reproducibility in heating schedules are achieved through digital control. Dilatometer control and data acquisition functions are accomplished by a minicomputer using a standard interface bus. Areas for further development are also discussed.

This work was supported by the U.S. Department of Energy (DOE), under Contract DE-AC04-76-DP00789.

A U.S. DOE facility.