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The nonlinear effect is one of the characteristics of photodetectors. In infrared measurement systems, photodetectors like MCT, InGaAs and InSb are widely used; while their non-linearity is still a problem. National Institute of Metrology, China has built an infrared spectral radiance measurement system. The system consists of a variable temperature blackbody as the standard radiation source; and uses a Fourier transform Infrared Spectrometer as the measuring instrument, including a MCT detector which is the main source of non-linearity uncertainty. In this study, an interpolation method and a polynomial fitting method are used to correct the non-linearity of the measurement system. To do so, at first, set the temperature of the standard variable blackbody to a serial of different temperatures, and use the measurement system to acquire the spectral response signal at each temperature; then, calculate the spectral radiance value of the standard radiation source based on the Planck’s law; after that, in the spectral dimension, analyze the relationship between and , and correct its non-linearity with a piecewise linear interpolation method and a multi-order polynomial fitting method; finally, verify the above two methods and analyze the relative deviation accordingly. The results show, the deviation is relatively large in wavelength range smaller than 8μm; while in 8μm~14μm wavelength range, the relative deviation is around 0.5%~0.001% and around 1.0%~0.001% by using the piecewise linear interpolation method and polynomial fitting method, respectively.
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