| This thesis is based on "Advanced Space-based Solar Observatory(ASO-S)",the"Strategic Priority Research Program(Class A)" of the Chinese Academy of Sciences.Full-disc vector MagnetoGraph(FMG),as one of the three major loads,the main scientific exploratory task is to measure the solar full-disc vector magnetic field,study the occurrence,development,interaction,and the resulted consequences of the solar magnetic field,and further understand the internal physical mechanism of flares and coronal mass ejection,as well as provide an observation basis for space weather event prediction.In view of the stability and accuracy requirements of FMG on-orbit observation of the solar magnetic field,the thesis starts from the solar magnetic field measurement principle and instrument design requirements,and conducting the following research work on the FMG entrance window,optical system,and optical system polarization characteristics:Firstly,the measuring principle and method of the solar magnetic field based on the Zeeman effect are introduced.For different measurement methods,the key optical system composition of the solar magnetic field telescope is analyzed in detail.The composition and advantages and disadvantages of imaging optical system and polarization optical system with different structure forms are compared,which lays the foundation to the selection of optical system of solar magnetic field telescopes.Secondly,in response to the in-orbit adaptability issues of the FMG optical system,the optical incident window of the FMG is studied.A summary and analysis were firstly conducted on the impact of the complex space environment of the ASO-S on optical glass and coatings,based on which fused quartz glass was chosen as the material for the incident window.Subsequently,through simulation and comparison studies of three different structural incident windows-cemented,monolithic,and double separationfor their thermal stability,the double separation structure was selected as the initial structure for the incident window.Then,combining the above research,the configuration of coatings for the incident window was proposed.Finally,the impact of several major space environmental factors,such as ultraviolet radiation and electron radiation,on the performance of the incident window faced by the FMG was investigated through experimental research.Thirdly,based on the measurement principle of the solar magnetic field with the Zeeman effect and the imaging characteristics of the optical system,the source of the polarization measurement error of the optical system is analyzed.An evaluation model between the optical system and polarization measurement accuracy was firstly established using scalar diffraction theory and aberration theory and combined with the solar magnetic field measurement principle.The results show that the error change tends to be constant when the RMS value of wave aberration of the optical system better then λ/38;according to FMG’s instrument measurement accuracy requirements,when the RMS value of wave aberration of the imaging optical system is λ/25,it can meet and exceed the observation requirements of the polarization background of the FMG measurement system of 0.0005Ic and the polarization crosstalk error of 0.015.Subsequently,the influence of instrument polarization characteristics of the imaging optical system on the accuracy of system polarization measurement was analyzed.Based on the description of polarized light with Stokes parameters,the polarization transmission model of the FMG optical system was then established;the influence of the polarization effect of the incident window,optical telescope,imaging system,polarization beam splitter,and quarter-wave plate optical elements on the polarization measurement accuracy of the system is analyzed through numerical simulation.This thesis provides a theoretical basis for the early design of the FMG and other optical systems used for polarization measurement and the evaluation of system measurement accuracy in the later stage.Finally,according to the FMG scientific observation requirements of 532.4 nm wavelength and 1" resolution,an optical system scheme with low polarization background,small crosstalk,simple polarization model,and photon-loss free is designed.To meet the accurate measurement requirements in orbit,a calibration and focusing scheme for the optical system was designed,and the structure of the incident window was optimized,reducing stray light by 68.61%after optimization.To verify the performance of the imaging optical system of the FMG,an optical polarization characteristic test platform was built,and the measurement results showed that the optical imaging quality and instrument polarization error of the FMG incident window and imaging optical system meet the measurement accuracy requirements of the FMG system.Finally,after comparing the observation results of the FMG with those of other similar solar magnetic field telescopes,the results showed that the on-orbit observation accuracy of the FMG was much higher than that of ground-based solar magnetic field telescope.In the observation of the details of a local longitudinal magnetic field,it was almost identical to the most advanced HMI observation results internationally. |
