International
Tables for Crystallography Volume D Physical properties of crystals Edited by A. Authier © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. D. ch. 1.4, pp. 102-103
Section 1.4.3.3. Optical methods (interferometry)
a
Institut für Geowissenshaften, Universität Kiel, Olshausenstrasse 40, D-24098 Kiel, Germany |
The basic principle of measuring thermal expansion by interferometry consists of converting sample-length changes into variations of optical path differences of two coherent monochromatic light beams, which are reflected from two opposite end faces of the sample (or planes corresponding to them). An He–Ne laser usually serves as a light source. A beam expander produces a parallel beam and interference by two planes, which are slightly inclined to each other, produces fringes of equal thickness. Thermal expansion causes a movement of this fringe pattern, which is detected by photodiodes. The number of fringes passing a reference mark is counted and gives a measure of the relative movement of the two planes.
As examples for various realizations of interferometric devices (Hahn, 1998), two basic designs will be described.
References
Hahn, T. A. (1998). Thermal expansion measurements using optical interferometry. In Thermal expansion of solids, edited by C. Y. Ho, ch. 6. Materials Park, Ohio: ASM International.Google Scholar