Effects of Detector Nonlinearity on Spectra Measured on Three Commercial FT-IR Spectrometers

Abstract

The effect of the nonlinear response of mercury-cadmium-telluride (MCT) detectors has been evaluated on three commercial Fourier transform infrared (FT-IR) spectrometers. The greater the photon flux and the photon flux density, and the smaller the area of the detector on which the source image is focused, the greater are the effects of the nonlinearity. The signal-to-noise ratio (SNR) of spectra measured with an MCT detector under conditions of high photon flux and, especially, high photon flux density is significantly less than the SNR calculated by using the manufacturer's D* value. Detector nonlinearity usually leads to negative deviations in Beer's law plots. An empirical correction algorithm has been applied to Beer's law spectra acquired with the use of photoconductive MCT detectors and has been found to work well.