TESTING THE RADIOMETRIC ACCURACY OF FOURIER-TRANSFORM INFRARED TRANSMITTANCE MEASUREMENTS

We have investigated the ordinate scale accuracy of ambient temperatur e transmittance measurements made with a Fourier transform infrared (F T-IR) spectrophotometer over the wavelength range of 2-10 mu m. Two ap proaches are used: (1) measurements of Si wafers whose index of refrac tion are well known from 2 to 5 mu m, in which case the FT-IR result i s compared with calculated values; (2) comparison of FT-IR and laser t ransmittance measurements at 3.39 and 10.6 mu m on nominally neutral-d ensity 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 ar e performed. (C) 1997 Optical Society of America.