Research On Airborne Mid-wave/Long-wave Dual Color Infrared Optical Systems

Infrared technology has been widely utilized in military,remote sensing,industry,medicine and other fields because of its advantages of passive work,all-time,not susceptible to interference and so on.In the field of infrared imaging,the two most widely utilized atmospheric window bands are the mid-wave band of 3-5 ?m and the long-wave band of 8-12 ?m.These two bands have different advantages and limitations.With the development of the new generation of dual-band/multiband infrared detector technology,the use of multiband imaging has become more and more extensive.In order to successfully apply the new generation detectors,it is necessary to design optical systems that can simultaneously have the ability of multiband imaging.Compared with monochromatic infrared system,the number of materials that can be selected for mid-wave/long-wave dual-band infrared optical system is significantly reduced,and the dispersion characteristics of materials change obviously in different wavebands.Chromatic aberration correction is the main problem in the design of dual-band optical system.Airborne constraints,such as small size,light weight and harsh thermal environment,also put forward higher requirements for infrared imaging equipment with long focal distance,large aperture and high resolution,which increases the difficulty of optical system designIn order to meet the urgent needs of the design of multiband infrared optical system,this paper studies some key technologies of airborne mid-wave/long-wave dual-band infrared optical system.We propose the method of accurate selection of optical materials.We propose a non-rotationally symmetric field mapping method for back-scanned step/stare imaging system,which can make all field points stable on the focal plane array during back-scanning.We design and development a dual-band infrared detection system and a large aperture and long focal length mid-wave/long-wave dual-band infrared optical system.The main research contents and contributions are as followsAiming to the problems of less available materials and difficulty in correcting wide band chromatic aberration,this dissertation proposes a calculation evaluation method to select materials for dual-band infrared optical imaging systems.The criterion includes the absolute lens power and the average defocus evaluated at a number of wavelengths in the designing radiation waveband.Evaluation of all potential combinations of materials by using this method,we can obtain the optimal combination of materials and the initial focal power distribution for optical components rapidly and efficiently.Through analysis and evaluation,ZnS/IG2 is the best two-lens material combination mode for mid-wave/long-wave dual-waveband infrared optics.Ge/ZnS/GASIR1 is the best three-lens material combination mode for mid-wave/long-wave dual-waveband infrared optics.We prove that the method is valued through designing and analyzing the combinations detailed.These best combinations can be used as lens elements to provide a good starting point for designing actual optical systemsIn order to meet the requirements of light weight,large relative aperture and low self radiation of the dual band infrared detection system,an infrared imaging system is designed by adopting the structure of catadioptric optical system..The working waveband are 3.7 ?m?4.8 ?m and 7.7 ?m?9.5 ?m.The focal length is 150 mm,and The F number is 2.Through design optimization,the modulation transfer function(MTF)of all field of views at the Nyquist spatial frequency of 33.31p/mm are close to the diffraction limit.The axial and vertical chromatic aberration are well suppressed,The cold stop matching is 100%,and the equivalent black body temperature of the optical system itself is only 233KAddressing the problems of off-axis field point wander and image blurring caused by the use of fast steering mirror(FPA)in back-scanned step/stare imaging system,this dissertation proposes a non-rotationally symmetric field mapping method for back-scanned step/stare imaging system,which can make all field points stable on the FPA during back-scanning.The mathematical model of non-rotationally symmetric field mapping between object space and image space is established Meanwhile,a back-scanned step/stare imaging system based on the model is designed,in which this non-rotationally symmetric mapping can be implemented with afocal telescope including freeform lenses.Experimental results show that this non-rotationally symmetric field mapping can provide the highest contrast images for back-scanned step/stare imaging systemAn airborne mid-wave/long-wave dual-band infrared optical system with large aperture and long focal length is designed.The detector is a Stirling cooled 320 × 256 dual-color infrared focal plane array with a pixel size of 30?m×30?m.With catadioptric optics and the folding around of plane mirrors,the size and weight of the infrared optical system are greatly reduced.The volume of the optical system is compressed by the aspheric main mirror with high gradient and fast focal ratio.The axial and vertical chromatic aberration are well corrected,and the MTFs of mid-wave band and long-wave band are close to or reach the diffraction limit.The aperture of the optical system is 220mm and the focal length is 880mm.In order to realize the rapid production and low cost of products,the main mirror and secondary mirror are made of aluminum alloy,and the optical manufacture is completed by means of single point diamond turning.The image of the device under static and dynamic conditions is tested by remote outdoor observation and the images are excellent.