Study On Long-wave Infrared Imaging Spectrometer With Smile Eliminated

Imaging spectral technique is an emerging photoelectric detecting technique,and can get both spatial and spectral information of the target. Due to the spectralcharacteristics of the long-wave infrared, imaging spectrometer of this waveband iswidely used in military and civilian areas, such as geographical remote sensing,detection of chemical gas, military target detection and thermal fluent analysis.Based on the maturity, efficiency and the advantages of energy and cost inlong-wave infrared of plane blazed reflection grating, we choose plane blazedreflection grating as beam split element, which is one of the core components ofimaging spectral system. In order to ensure the accuracy of data collection and thefeasibility of image processing, smile and keystone should be very small in theimaging spectral system. However, a larger smile and keystone will be produced byplane grating. So it is necessary and meaningful whether theoretically or practicallyto solve the problem of smile and keystone. The specific research contents include:1. The calculation method of the initial structure of the coaxial three-mirrorsystem is detailed. And it is discussed that the relationship between intermediateimage and values of profile parameters and focal length of the system. Depending onthe requirements of application, we simulate and design the off-axis three-mirrorsystem without intermediate image.2. The smile and keystone caused by grating are calculated. It is proposed for the first time that using off-axis lens to correct the smile and keystone. Thecharacteristics of eliminating smile and keystone of off-axis lens are analyzed.According to the vector diffraction theory, we analyze the diffraction characteristicsof plane grating. The formulas of the image height of two-dimensional field in tiltedimaging system are also deduced. Then, the smile and keystone caused by planegrating in Gaussian imaging system and tilted imaging system are calculatedrespectively. Finally, the elimination of smile and keystone of the off-axis lens isstudied by means of spatial ray tracing. It provides theory for the design of imagingspectrometer with smile and keystone eliminated.3. Collimating lens with small distortion and secondary imaging lens with100%efficiency of cold aperture are designed. The spectrophotometric systems withrefraction and reflection structure are compared, and the results show that thereflective structure is difficult to optimize the rational optical system with coldaperture and no obscuration. However, for refractive system, the rationalconstruction with100%efficiency of cold aperture and no obscuration can berealized through secondary imagery method.4. The imaging spectral system is optimized; the image quality and tolerance isanalyzed. The system designed has good image quality, tight structure and loosetolerance distribution. The maximum of smile and keystone of the optical systemdesigned are8.17μm and13.64μm, respectively. Both of them are less than half thepixel size of the detector. Plane blazed grating is used in the system to split the light,and it will work in pushbroom mode. The optical system with main performances ofhigh spectral resolution of32nm, spatial resolution of0.15mrad, focal length of200mm and F number of2is obtained.