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Proceedings Paper

Measurement of low-absorption optics by thermal imaging
Author(s): Alan F. Stewart; William Hughes
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Paper Abstract

An infrared camera system has been used to measure absorption in optical coatings and substrates. Laser light is directed at the test sample and milliwatts of power are absorbed. The camera images the surface of the sample and provides a direct measurement of the 8-12 micron radiation emitted. By considering the effective emissivity of the sample and the ambient temperature, the surface temperature of the sample is obtained. Through the use of an equivalent "reference" sample which is not heated by the laser, background variations may be effectively eliminated. The application of standard calorimetric methods to infrared imaging as well as the availability of improved sensors such as the microbolometer array has led to our ability to resolve temperature excursions as low as 0.01°C with a S/N of 20 for typical samples. The IR imaging method has been used to evaluate many optical coatings and window materials for the Airborne Laser program. Because the method is noncontact, it has been used to directly measure absorption on large optical surfaces. In some instances, defects have been observed and mapped using this method. Variations in absorption which might be predicted from the coating design have been measured directly. The IR imaging technique thus offers great flexibility and sensitivity comparable to precision calorimetry.

Paper Details

Date Published: 15 January 2007
PDF: 11 pages
Proc. SPIE 6403, Laser-Induced Damage in Optical Materials: 2006, 64031H (15 January 2007); doi: 10.1117/12.696277
Show Author Affiliations
Alan F. Stewart, Boeing Directed Energy Systems (United States)
William Hughes, Lockheed Martin Missiles and Space (United States)

Published in SPIE Proceedings Vol. 6403:
Laser-Induced Damage in Optical Materials: 2006
Gregory J. Exarhos; Arthur H. Guenther; Keith L. Lewis; Detlev Ristau; M. J. Soileau; Christopher J. Stolz, Editor(s)

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