Comparison of noise sources in dual- and single-beam Fourier-transform near-infrared spectrometry

We report the results of noise source investigations and stability tests in both dual- and single-beam Fourier-transform near-infrared operation. The noise sources are divided into two parts: intrinsic and extrinsic. The intrinsic noise sources, which include detector system noise, are common for both modes of operation. The extrinsic sources, which include variations in ambient conditions (room temperature, atmospheric gaseous components, and source scintillations), are shown to be smaller in dual-beam operation than in single-beam operation by a factor of 2-10. The results are based on interferograms measured in specified time intervals. The root-mean-square values are calculated at each retardation point. The values obtained near the centerburst and average values obtained for the dual-beam operation are compared with the intrinsic noise value obtained for single-beam operation. The dual-beam advantage is observed in both open-beam and liquid cell measurements, and it corresponds well with earlier results based on multivariate calibration techniques applied on aqueous solutions.