Testing the radiometric accuracy of Fourier transform infrared transmittance measurements

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Abstract
We have investigated the ordinate scale accuracy of ambient temperature transmittance measurements made with a Fourier transform infrared (FT-IR) spectrophotometer over the wavelength range of 2–10 µm. Two approaches are used: (1) measurements of Si wafers whose index of refraction are well known from 2 to 5 µm, in which case the FT-IR result is compared with calculated values; (2) comparison of FT-IR and laser transmittance measurements at 3.39 and 10.6 µm on nominally neutral-density filters that are free of etaloning effects. Various schemes are employed to estimate and reduce systematic error sources in both the FT-IR and laser measurements, and quantitative uncertainty analyses are performed.