Nonlinearity measurement for MCT detector by means of flux superposition method based on single and dual light laser source

The accurate nonlinearity measurement with broad range is essential for the application of MCT detectors. The MCT detector nonlinearity experimental result reported in the literature was obtained from the single-light source or dual-light source method, respectively. However, the range of the measurement nonlinearity from just single or dual light source method is relatively limited, and their consistency is difficult to be studied. Furthermore, the filter and optical gate were adopted for the single-light source method in the literature, introducing uncertainty due to multiple reflections. Therefore, to obtain the nonlinear measurement results of a wide range of MCT infrared detectors, an experimental system was designed by combining the single laser light and dual laser light source schemes in this paper. To eliminate the influence of multiple reflections of the light path in the traditional single light source scheme, a high absorptivity optical trap is used to replace the optical gate and filter as the light path on-off controller. Then, the nonlinear measurements for different MCT detectors were carried out at 4 μm. The single nonlinear and integrated nonlinear measurement results are obtained with the irradiance range of (4.6 × 10^-5∼4.7 × 10^-2) mW/cm². The measurement results show that the two methods exhibit a high degree of consistency in the overlapping area. And the nonlinear characteristics of MCT detectors with different spectral responsivity have high consistency in the illumination measurement interval. Furthermore, the relative deviation between the MCT detector nonlinear measurement results and National Physical Laboratory (NPL) results is within the claimed degree of certainty.