Fig. 1. Retrieval error of column concatenation for carbon dioxide under different spectral resolving powers

Fig. 2. Signal-to-noise ratio of imaging spectrometer under different F-numbers

Fig. 3. Structures of optical splitting system. (a) Chrisp-Offner structure; (b) Littrow-Offner structure; (c) RT structure

Fig. 4. Structure scheme of designed optical system

Fig. 5. Structure diagram of designed optical system

Fig. 6. Optical path diagram of symmetric double off-axis three-mirror structure

Fig. 7. System wavefront at different wavelengths. (a) 1.90 μm; (b) 2.40 μm

Fig. 8. MTF curves and spot diagrams of system at the central wavelength. (a) MTF curves; (b) spot diagrams

Fig. 9. Smile and keystone of system. (a) Smile; (b) keystone

Fig. 10. Symmetric double off-axis three-mirror structure after introducing freeform surfaces

Fig. 11. System wavefront at different wavelengths after introducing freeform surfaces. (a) 1.90 μm; (b) 2.40 μm

Fig. 12. MTF curves and spot diagrams of system at the central wavelength after introducing freeform surfaces. (a) MTF curves;

Fig. 13. Smile and keystone of system after introducing freeform surfaces. (a) Smile; (b) keystone

Fig. 14. Spectral response function curves at different wavelengths after introducing freeform surfaces. (a) 1.90 μm; (b) 2.15 μm;