11 October 2000 Fourier transform spectrometer for thermal-infrared emissivity measurements near room temperatures
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The NRLM has developed a Fourier transform infrared spectrometer to measure spectral radiance of thermal-infrared emission near ambient temperatures with high accuracy. The spectrometer uses a simple Michelson interferometer that consists of corner cube mirrors and a KBr beam splitter. The spectral range between 5 (mu) m and 12 (mu) m was covered by a photovoltaic HgCdTe detector. For calibration and compensation for the offset drive, the spectrometer was equipped with two high quality reference blackbodies, a fixed-temperature blackbody cooled by liquid nitrogen and a variable temperature blackbody operated in the temperature range between -20$DEGC and 100$DEGC. The calibration procedure based on the advanced phase correction technique was applied to observed spectrum to complete reconstruction of the emission spectrum. Several tests were performed to check characteristics of the spectrometer. The results showed that the size-of-source effect (SSE) of the FTIR-spectrometer is negligibly small for a target larger than 20 mm diameter. We carried out an experiment to check the linearity between incident and measured spectral radiance inside the calibration levels by measuring the radiance from a third blackbody between -20$DEGC and 100$DEGC after calibration using the liquid nitrogen cooled blackbody and the fluid bath blackbody fixed at 100$DEGC. Observed non-linearity normalized at the blackbody radiance of 100$DEGC was smaller than the 0.5% around 10 (mu) m bands.
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Juntaro Ishii, Juntaro Ishii, Akira Ono, Akira Ono, } "Fourier transform spectrometer for thermal-infrared emissivity measurements near room temperatures", Proc. SPIE 4103, Optical Diagnostic Methods for Inorganic Materials II, (11 October 2000); doi: 10.1117/12.403578; https://doi.org/10.1117/12.403578

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