Design of long-wave infrared imaging spectrometer with eliminating spectral curvature

To achieve the long-wave infrared hyperspectral imaging for remote sensing targets and to eliminate the spectral curvature of a plane grating effectively, a long-wave infrared imaging spectrometer with an off-axis lens was designed. The spectral curvatures from the plane grating and a single off-axis lens were calculated, respectively, and the relationships between spectral curvatures and relative parameters were analyzed, then an initial structure for eliminating spectral curvature was designed. The optical system optimized shows an aperture of 100 mm, F number of 2, spectral resolution of 20 nm, spatial resolution of 150 μrad, and a cold aperture efficiency of 100%. Moreover, its image quality is close to the diffraction limit and the spectral curvature of system changes from more than 180 μm to less than 14.3 μm. The design obtains a universal eliminating spectral curvature formula, and proves that the off-axis lens has the function to eliminate spectral curvature. It concludes that the imaging spectrometer of plane grating using off-axis lens can offer a spectral curvature less than half the pixel size of the detector without increasing the system complexity, which meets the use request on the premise of satisfying imaging quality.