Comparison of near-infrared transmittance and reflectance measurements using dispersive and Fourier transform spectrophotometers

A spectrophotometer based on an integrating sphere coupled to a commercial Fourier Transform Infrared (FTIR) instrument has been constructed for regular spectral transmittance and reflectance measurements over the 1 mum to 18 mum wavelength region. Despite the large number of sources of error that often limit the radiometric accuracy of FTIR measurements, we demonstrate uncertainties similar to established dispersive instrumentation. We performed near-normal-incidence reflectance and transmittance measurements on a series of samples over the 1 mum to 2.5 mum wavelength range using both FTIR and dispersive spectrophotometers. The results are compared, taking into account any differences in measurement geometry among the various systems and the combined measurement uncertainty. We find agreement within the combined uncertainties over most of the measured spectral region.