Research On Optical Design Method Of Dispersive Imaging Spectrometer Based On Freeform Surface

Imaging spectrometer is an optical instrument that can perform imaging and spectral information detection at the same time.Since its inception,it has played an important role in various disciplines.However,scientific research has never-ending requirements for the quality of spectral data,which is the internal cause of the continuous development of imaging spectrometers,which drives the continuous improvement of imaging spectrometers in the direction of larger field of view,higher resolution,and more compact volume.Imaging spectrometers based on traditional surface shapes have been difficult to meet these requirements.Optical freeform surface generally refers to an optical surface without rotational symmetry,which has a high degree of freedom in optimization,strong surface shape controllability,and can correct aberrations caused by asymmetry in off-axis optical systems.The application of optical freeform surfaces in the design of imaging spectrometers helps to achieve high-demand imaging spectrometer designs.Therefore,the design of freeform imaging spectrometer has become a hot research direction in the field of spectrometer design today.However,in the design of freeform optical systems,there are problems such as few initial structures,unclear design directions,and large design blindness.In this regard,this paper: First,a grating mid-wave infrared grating spectrometer system is designed using non-freeform surface.The system adopts the classic C-T structure,uses aspheric mirrors to improve image quality,and adds cylindrical mirrors to compress astigmatism.The design is compact,but the residual aberration causes the designed spectrometer to still not meet the needs of imaging and spectral detection at the same time.In this regard,the feasibility of performance improvement brought by freeform surfaces is analyzed,and optical freeform surfaces are proposed to be used for further improvement.Secondly,the surface shape characterization method of optical freeform surface in freeform optical system is studied.The XY polynomials,Zernike polynomials,Q-Type polynomials and radial basis functions are investigated to characterize the optical freeform surfaces.Among them,the XY polynomial has a simple mathematical form,is closely related to optical processing,and has strong adaptability to different aperture shapes.It is suitable for the design of freeform imaging spectrometers.Therefore,XY polynomial is selected as the surface shape characterization method of freeform imaging spectrometers.Then,aiming at the problems of insufficient modularity and slow solution speed in the existing design methods of the initial structure of freeform optical systems,a new method is proposed that can directly obtain initial freeform optical systems with good optimization potential from the plane afocal system.Using this method,the design of a compact off-axis two-reflection telescope is completed,and the design results of the existing traditional surface C-T spectrometer are improved.The successful design of the two optical systems verifies the feasibility of the design method.Finally,in view of the problem of strong design blindness in the existing initial structure design methods of freeform optical systems,a design method is proposed that can select the structure form of the curved prism imaging spectrometer that saves the most design resources.Using this method,the design of a curved prism free-form imaging spectrometer is completed,which verifies the feasibility of the proposed method.