Research On Application Of Free-form Surface In Large Field Of View Infrared Camera

Space remote sensing technology is at a period of rapid developing,as requirements for the resolution rate and width of satellite image have increased,the application of regular spherical and aspherical optical systems can hardly achieve these performance.Free-form surface,with its property of non-rotational symmetry,complex surface variation and a wide range of designing freedom,has provided enough optimization variables for optical system design.The image quality of the off-axis optical system can be further improved by applying free-form surface optimization.Meanwhile,key technologies like lightweight,large FOV and low F number now have become the core competitiveness of space infrared camera,thus the free-form surface is playing a vital role.The main content of this thesis is as below:According to the problem of space camera's small FOV,this thesis designs an offaxis three-mirror optical system with wide FOV.Detailed index and initial structure parameters of this optical system have been calculated and analyzed.Starting with the coaxial three-mirror optical system,through decentering and tilting,processing both mirror tilting and surface description,a Cook-TMA with field angle of 30°×10° has been obtained.Derived from paraxial aberration theory,this paper also elaborates the variation of each aberration in the off-axis optical system.This paper elaborates a variety of free-form surface design methods and principles,through analysis and comparison,select a reasonable design.Designing the main reflector mirror of wide field off-axis three-mirror optical system by Zernike polynomials free-form surface,which has achieved improved performance when compared to even aspheric surface method.Merit and demerit of free-form surface application are also analyzed.This thesis also introduces the processing technology of optical free-form surface by classification,analyses the basic procedure of ultraprecision digital control processing,analyses the necessity of multiple circular module of processing and testing,the basic principles of free surface processing method selection are established.Meanwhile,this subject starts from testing methods of aspherical surface,demonstrates testing accuracy and rationality of zero-compensation CGH,then the basic route of the free surface detection scheme is developed.This thesis uses the ray tracing to get surface discrete point data of the main reflector mirror,and matches the points to obtain the free-form surface shape.This thesis starts with correlated properties of the free-form surface,applies it into off-axis three-mirror system and verifies its superior performance of expanding FOV,correct aberrations and simplifying structure The results show that the free-form surface has great advantage in improving the image quality of off-axis system.Compared to aspheric surface,the average transfer function of the free-form system has improved above 0.09,which approaches the diffraction limitation,90% of the imaging points are in the range of Airy disk,the energy concentricity is above 0.9 within 15?m diameter.The application of Zernike free-form surface in off-axis three-mirror system is good and the imaging performance has been enhanced greatly.