| As the outer atmosphere of the sun,the corona is the main disturbance factor of the solar-terrestrial space environment.In order to perform ground-based spectroscopic imaging of CMEs（Coronal Mass Ejection）and MHD（Magnetohydrodynamic）waves in the field of view of the coronal source region above the solar surface in the range of0.05～1.0 R⊙（R⊙denotes the solar radius）,as well as to obtain the spectral images and primordial characteristics of CMEs and the image characteristics of MHD waves in the perihelion region,an internally masked transmission coronagraph with a flux aperture of 200 mm is designed in this thesis.Compared with the current internationally operating Inner Occulteded ground-based coronagraphs,its MTF（Modulation transfer function）is already close to the diffraction limit,and it is chosen to have stronger radiation in both the coronal hole and active region,which is suitable for studying the low-temperature spectral lines of Alfvén waves with different magnetic field structures for observation.Based on the international existing experience of coronagraph development,the internal occultation coronagraph developed in this thesis adopts a dual optical path structure of the main optical path and the splitting optical path,with the splitting optical path mainly responsible for the control of pointing accuracy.The main parameters of the system are:field of view±1.05～±2.0 R⊙（distance from the sun center）,pixel size of 13.5μm,MTF of 0.76（@37lp/mm）at 0.262°field of view and 0.73（@37lp/mm）at0.542°field of view,and its central wavelength of FeⅩ637.4 nm（alternative FeⅪ792.8 nm）,the system F-number is 5.8,the total length of the optical system is 3769.75mm,the focal length is 1160 mm,and the total system length is 4339 mm.The most important indicator in the design of coronagraphs is the suppression level of image plane stray light,which is 10-6 B⊙（B⊙indicates the average solar brightness）of the photosphere into direct light.The coronagraph defines stray light as three levels according to the PST（Point Source Transmittance）test standard,the first level is the photospheric layer of direct light;the second level is the diffraction of the objective diaphragm,the image plane stray light level is 10-5 B⊙;The third level is the secondary reflection ghost image of the objective lens itself.The stray light level on the image plane is 10-6 B⊙,which is on the same order of magnitude as the coronal light of 1.05R⊙;The fourth level is the scattering from the sky background and other stray light introduced by dust,scratches,surface roughness on the lens and lens impurities.For the direct light we suppress it by internal mask reflection.For diffracted stray light,we mainly apply plane wave diffraction and boundary wave diffraction theory to calculate diffracted light,and combine with ray tracing method to design Lyot spot to mask diffracted light.The objective mirror itself ghost image is absorbed on the front surface of the first lens of the relay mirror set by plating a 1mm chromium film by photolithography and electron beam vaporization method.We designed the adjustable displacement mask assembly based on the optical design,which allows focusing compensation for the spectrum in the 500～820 nm band.And based on Kirchhoff’s radiation law,we established the inverse model of absorbance of different materials.A complete surface radiation model is established in combination with atmospheric optics.The temperature change of different materials and the stress displacement of the mask bottom surface are calculated by the optical-thermal coupling model,and the correctness of the model is verified by experiments.The approach optimizes the suppression method of direct light and reduces the loss of coronal information over thousands of kilometers.To optimize the stray light detection accuracy,a new spliced detection method is proposed,which can find the scattered imaging position of the emitting surface before the relay mirror group by controlling the spatial position of the simulated light source and the size of the emitting aperture under laboratory conditions,where the detection error can be reduced by absorbing it.And an OEBC（Optimized Expanded Boundary Algorithm）based on T-matrix is established to expand the Non-Sphericalized scattering of Mie theory,showing the surface field distribution and computational errors of ellipsoidal and oblate spheres,which can be further analyzed by calculating the visualized particles in the localization region and optimizing the coronagraphic stray light theory from the computational point of view.Optimization of coronagraphic stray light theory from a computational point of view by combining the particle surface accumulation efficiency model.A Lyot-type birefringent cascade filter was designed due to the requirement of wavelength shift of the heliopause spectral line,and its final parameters and design structure were determined.Finally,the stray light of the conventional system is detected in the image face of the coronagraph,and the stray light can reach 6x10-6B⊙（at 1.05 R⊙）,5x10-7B⊙（at 2.0 R⊙）.The stray light level can be reduced by at least one order of magnitude after splicing detection.The final systematic stray light detection of the coronagraph at the image plane can reach stray light levels of 6x10-6 B⊙（at 1.05 R⊙）and 5x10-7 B⊙（at 2.0 R⊙）. |
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