Fig. 1. Schematic of the nonlinearity measurement and the radiation flux superposition apertures

Fig. 2. Drift characteristic of the blackbody radiation source measured by LP4

Fig. 3. Drift characteristic of the blackbody radiation source measured by FTIR (a) relative drifts of spectrums measured by DTGS detector，(b) relative drifts of spectrums measured by MCT detector

Fig. 4. Nonlinearity measurement results and uncertainties at wavelengths of 3.9 μm and 10.6 μm (a) measurement results and uncertainties measured by DTGS detecto, (b) measurement results and uncertainties measured by MCT detector

Fig. 5. Repeatability of nonlinearity measurement results at the wavelength of 3.9 μm measured by DTGS detector

Fig. 6. Integral nonlinearity measurement results, comparisons and uncertainties