Simulation Of The Optics Design Of The Wide Field Of View Soft X-Ray Imager And Analysis Of Its Imaging Performance

The soft X-ray has a relatively high reflection efficiency when the grazing-incidence angle is less than 1°.The conventional Wolter-type soft X-ray imaging telescope is a grazing-incidence focusing imaging system with a single optical axis,generally its field of view is only tens of arc minutes.The imaging method of soft X-ray imager based on lobster-eye optical imaging principle is different from that of the Wolter-type soft X-ray telescope.It has a spherical multi-optical axis micro-channel optical structure which is similar to compound eyes structure,and can theoretically achieve high resolution in 4?field of view.With the development of space technology,the application of wide field of view soft X-ray imager has become more and more urgent.At the same time,the advancement of ultra-precision micro-machining technology has greatly promoted the lobster-eye-type wide-field soft X-ray imaging equipment into engineering application stage in the past ten years.The research work of this paper takes Sino-European joint space science mission:Solar Wind Magnetosphere Ionosphere Link Explorer(SMILE)as the engineering application background to carry out the optical design simulation and image quality analysis of wide field of view soft X-ray imager(SXI),providing powerful observation and data analysis methods for large-scale exploration of the coupling mechanism between the solar wind and the Earth's magnetosphere and the evolutionary model of its dynamic processes.Thanks to the release of soft X-rays from the charge exchange process between solar wind particles and neutral atmospheric components in the near-Earth space,the wide field of view soft X-ray imager will monitor the Earth's magnetospheric boundries and its dynamic changes using the lobster-eye optical system in the soft X-ray band of 0.2~5keV,including the location,shape and motion of bow shock,dayside magnetopause and cusps.According to the structure of ideal lobster-eye optics,the principle of total reflection and the calculation of interface reflectivity in X-ray band are introduced.The characteristics of special"cross-shaped"image spot for point light source imaging are discussed.The focal length and relationship between the object and the image are derived and the imaging indicators of lobster-eye optical system including field of view,spatial resolution,effective area,and focusing efficiency are given.Aiming at the lack of lobster-eye optical system simulation tool that can be used for engineering,this paper focuses on the establishment of optical imaging simulation model based on lobster-eye principle and the development of optical imaging software,as well as image quality analysis based on simulation results.The mathematical model of lobster-eye optics with a tens of million-level micro-channel structure and spherical surface is established.The ray-tracing algorithm of the whole imaging process is designed.The parallelized program is coded.Finally,the visualization lobster-eye optical simulation software is developed and verified by the demonstrations of point and surface light sources imaging.According to the application scenario of SXI,the composition and working principle of SXI prototype are introduced from straylight baffle,filter,lobster-eye focusing component,CCD detector and high-energy particle shielding door,and the optical imaging requirements of the prototype are given.Based on developed simulation software,the influence of lobster-eye optics parameters on imaging resolution,effective area and focusing efficiency was analyzed systematically.Combined with the imaging requirements of SXI prototype,the micro-channel aspect ratio of lobster-eye component is optimized to 30 when the radius of curvature is600mm.The spatial resolution is about 6 arc of minutes and the total optical effective area is about 17.84cm~2 when the energy of incidenct X-ray is 0.5keV.In addition,several defects of the lobster-eye optics in the installation and manufacturing process are analyzed in combination with the actual process.The defective lobster-eye models are established,the corresponding imaging algorithms are designed and the imaging differences between the defective and ideal lobster-eye optics are analyzed.