Absolute Specular Reflectance Measurements In The Infrared

Keith A. Snail; Arthur A. Morrish; Leonard Hanssen

doi:10.1117/12.936699

23 February 1987 Absolute Specular Reflectance Measurements In The Infrared

Keith A. Snail, Arthur A. Morrish, Leonard Hanssen

Proceedings Volume 0692, Materials and Optics for Solar Energy Conversion and Advanced Lightning Technology; (1987) https://doi.org/10.1117/12.936699
Event: 30th Annual Technical Symposium, 1986, San Diego, United States

Abstract

The absolute reflectance of specular surfaces can be measured with a "V-W" optical system invented by Strong. The most difficult systematic error to eliminate in a V-W measurement is drift of the beam spot on the detector surface with small angular shifts of the beam between the sample-in (W) and sample-out(V) positions. In the infrared, this problem is exacerbated by the nonuniformity and small size of available detectors. Previous researchers have minimized this error with integrating spheres (in the visible) and/or auxiliary optics which desensitize the system to sample tilt errors. In order to verify this sensitivity to beam drift, a set of angular response measurements were performed on a commercial, variable angle V-W accessory and then modelled with a CODE V raytrace. The absolute accuracy of the instrument was estimated by measuring the specular reflectance of silver from 2-20 microns and comparing it to a Hagens-Rubens model. Finally, a nonimaging concentrator and a gold integrating sphere are considered as ways to increase the effective area of the detector and thus further desensitize the optics to misalignment errors.

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Keith A. Snail, Arthur A. Morrish, and Leonard Hanssen "Absolute Specular Reflectance Measurements In The Infrared", Proc. SPIE 0692, Materials and Optics for Solar Energy Conversion and Advanced Lightning Technology, (23 February 1987); https://doi.org/10.1117/12.936699

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