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15 October 2012 Measuring grazing-angle DHR with the infrared grazing angle reflectometer
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The Infrared Grazing Angle Reflectometer allows measurement of Directional Hemispherical Reflectance (DHR) at very high angles of incidence (30 to 85 degrees) and at wavelengths ranging from 4.3 to 10.8 microns. A hemi-ellipsoidal mirror redirects the reflected light and reflects it on to a novel five-sided pyroelectric detector. The incident light intensity is measured and used in calculating the DHR of the sample. In this paper, the theory of operation of this detector is derived, and used to simulate the operation of the system. This simulation of the detector shows errors of 3% or less for both diffuse and specular samples, compared to the theoretical DHR. The calibration method defined in this paper allows for high accuracy and ease of use without knowing the specific attributes of the optics used in the system. Finally, collected DHR data is compared with the simulated data for comparison. Comparing the measured data to the simulation shows that the model correctly predicts the locations and trends of the scattered energy.
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Michael R. Benson, Michael A. Marciniak, and Jeffrey W. Burks "Measuring grazing-angle DHR with the infrared grazing angle reflectometer", Proc. SPIE 8495, Reflection, Scattering, and Diffraction from Surfaces III, 84950R (15 October 2012);

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