Optical Design Of An Integrating Sphere-Fourier Transform Spectrophotometer (FTS) Emissometer

Keith A. Snail; Kevin F. Carr

doi:10.1117/12.975519

13 October 1986 Optical Design Of An Integrating Sphere-Fourier Transform Spectrophotometer (FTS) Emissometer

Keith A. Snail, Kevin F. Carr

Proceedings Volume 0643, Infrared, Adaptive, and Synthetic Aperture Optical Systems; (1986) https://doi.org/10.1117/12.975519
Event: 1986 Technical Symposium Southeast, 1986, Orlando, United States

Abstract

This paper describes the optical design of an integrating sphere - Fourier Transform Spectrophotometer (FT S) instrument for measuring diffuse IR reflectance as a function of angle, temperature and wavelength. The integrating sphere is 5 inches in diameter with a center mounted sample stage permitting beam incidence angles of 10 to 70 degrees. Samples can be mounted back-to-back for relative measurements and ports are included for specular subtraction of the reflected beam at 20 and 60 degree incidence angles. A heater capable of producing temperatures over 150°C h'as been included in a sample mount on the wall of the sphere. In addition, the sphere can be rotated about the beam port, permitting operation in both the center and wall mounted modes. Two detectors are planned for the sphere: a 16 mm² square cooled HgCdTe detector and an uncooled 3 mm diameter DTGS detector which is coupled to the sphere with a nonimaging compound elliptic concentrator (CEC). The CEC restricts the detector's field-of-view (FOV) to uniform contrast areas on the sphere wall with essentially no change in detector flux. The sphere's coating consists of a 0.5 micron thick gold film on a aluminum substrate, with a mean feature size of approximately 20 μm; a similar coating with a roughness average of approximately 10 pm was also considered. Measurements of the 10 pm coating's total spectral reflectance from 0.3 - 20.0 pm and the bi-directional reflectance distribution function (BRDF) at 3.8, 10.6, and 20.0 μm are presented. The BRDF results show a Lambertian character in fixed azimuthal planes and no specular peaks until the wavelength equals 20 μm and the incident angle is 80 degrees.

Citation Download Citation

Keith A. Snail and Kevin F. Carr "Optical Design Of An Integrating Sphere-Fourier Transform Spectrophotometer (FTS) Emissometer", Proc. SPIE 0643, Infrared, Adaptive, and Synthetic Aperture Optical Systems, (13 October 1986); https://doi.org/10.1117/12.975519

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