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Interferometric Measurement of Temperature

IP.com Disclosure Number: IPCOM000073957D
Original Publication Date: 1971-Feb-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Alstad, JK: AUTHOR [+3]

Abstract

Shown is an optical schematic for temperature measuring apparatus using interference phenomenon. A source of coherent light S directs light to a transparent material 10. Some of the light from the source S is reflected directly to a converging lens 12, while other light is refracted into the transparent material 10 before it is reflected back out to the converging lens 12. Phase difference of the light at point P on the surface of the material 10 is the same as phase difference at point P1. The intensity of light is monitored at point P1. That intensity will vary in accordance with the interference between the directly reflected light and the refracted light.

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Interferometric Measurement of Temperature

Shown is an optical schematic for temperature measuring apparatus using interference phenomenon. A source of coherent light S directs light to a transparent material 10. Some of the light from the source S is reflected directly to a converging lens 12, while other light is refracted into the transparent material 10 before it is reflected back out to the converging lens 12. Phase difference of the light at point P on the surface of the material 10 is the same as phase difference at point P1. The intensity of light is monitored at point P1. That intensity will vary in accordance with the interference between the directly reflected light and the refracted light.

The thickness of the material 10 will, of course, vary as the temperature of the material. As the material 10 expands or contracts due to temperature changes, the conditions for interference will change, and the change in thickness may be detected by observing fluctuations in intensity at point P1. If these fluctuations in intensity from maximum to minimum at P1 are detected and graphed, then the change in thickness may be calculated by the expression Delta D = m Lambda Omnicron over 2n cos Phi/1/ where m is the number of cycles on the graph, Lambda Omnicron is the wave length of light, Phi/1/ is shown in the above figure, and n is the index of refraction of the transparent material 10. The change in temperature is then given by Delta T = 1 over K Delta D where K is...