For spatial-modulation imaging spectrometers, the conventional non-uniformity correction method cannot efficiently reduce the pattern noise caused by stationary interference fringes on the imaging plane. In this study, we apply optical the defocus method to realize scene-based non-uniformity correction. By applying severe defocusing, the diffraction effects can be neglected, and the point spread function of the system is equivalent to the geometric projection at the exit pupil. When the light of each spot is within the field of view, it illuminates the entire detector, and the detector obtains uniform irradiance. We can implement a single-point calibration or single-plus-two calibration using the uniform irradiance.
In order to achieve infrared imaging spectrometers for environmental gas monitoring in the medium-wave infrared and long-wave infrared spectra, meanwhile detecting the characteristic spectra of a variety of ambient gas molecules, it is necessary to do research on the design of the infrared wide spectrum (3.2μm～14μm) imaging spectrometers optical system with a large relative aperture. First of all, the lens power of reasonable distribution will be available by solving of the wide spectrum correcting chromatic aberrations equation and athermalization equation. Secondly, the list compares the common infrared optical material in the infrared wide spectrum dispersion characteristics and thermal characteristics differences, optimizes the three infrared optical materials of the Germanium single crystal, wide spectral Zinc sulfide, and Chalcogenide glass for transmission optical system design. Thirdly, using CODE V optical design software to optimize the optical parameters, the system uses four lenses, introduces four aspherical faces, the rest are spherical. Finally, the modeling gives the 3D layout of the system, and the image evaluation and tolerance analysis of the optical system are carried out. The results show that the modulation transfer function (MTF) value of the optical system at the spatial frequency 30lp/mm is greater than 0.5. The average square root (RMS) value of the diffused spot diameter is less than 17μm; The working band is 3.2μm ~14μm, F number 1, the optical system in the temperature range of -40°C ~+60 °C has a good imaging quality. The optical system has the characteristics of large relative aperture, wide working band, good process and compact structure, and can be used for 640×480 the infrared wide-spectral segment focal plane detector.
During the transmission of the thermal radiation in the atmosphere, the radiant energy is attenuated due to physical processes such as refraction, absorption, and scattering, which causes a change in the detection capabilities of the thermal imaging system. As a key performance of thermal imaging system, the inspection of the operating range is of great significance to the theoretical research and practical application of thermal imaging systems. Actually, the environmental condition that does not match the specified test condition when testing the operating range which are not encountered. It's complex to judge whether the thermal imaging system meets the index requirements by the test result directly. By modeling the target, analyzing and comparing the spectral transmittance under different atmospheric conditions, the paper introduces a method for judging the operating range of the infrared thermal imaging system when inspecting environmental deviates from the specified environment proposed.