QC 351 A7 no. 48 / New materials of low thermal expansion are finding wide application.
The expansion coefficient (a) is a function of temperature, and this function must be known for each material before its applicability can be assessed.
A novel method for determining a, which is at once precise and easily
implemented, has been devised. It is based on the dependence of mode frequencies in a Fabry-Perot interferometer on the mirror separation. The expansion sample is formed into an interferometer spacer with ends polished
flat and parallel. Spherical mirrors are optically contacted to the ends,
forming a confocal interferometer. The assembly is maintained at controlled
temperatures in an environmental chamber. The two lowest -order transverse
modes are probed by variable -frequency sidebands derived from a 633 -nm He-
Ne laser by amplitude modulation.
A change in sample temperature AT causes a change in interferometer
length AL, which shifts the resonance frequencies by Av. Then a = (1 /AT)
(AL /L) _ - (1 /AT)(iv /v). Thus, a can be measured with precision limited
ultimately by the stability of the source laser, in practice 1:109 with
presently available commercial lasers.
For a sample of Owens -Illinois Cer -Vit, a has been measured at 10 temperatures in the range 3.0 to 32.4 °C, with a mean error of 2 x10-9 and a maximum error of 3 x10 -9. For a sample of Corning ULE silica, a has been measured at six temperatures in the same range, with a mean error of <1 x10 -9
and a maximum error of <1.3 x10 -9.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/621642 |
| Date | 01 December 1969 |
| Creators | Bradford, James N. |
| Publisher | Optical Sciences Center, University of Arizona (Tucson, Arizona) |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | Technical Report |
| Rights | Copyright © Arizona Board of Regents |
| Relation | Optical Sciences Technical Report 48 |
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