Analysis Of Infrared Stray Radiation Of The Optical System Of A Large Ground-based Solar Telescope

As the last bands observed through the solar physical observation window,the midinfrared and far-infrared bands contain many new researching values.However,infrared astronomical research has great particularities in its background noise and detecting targets.Especially for the infrared observation of the sun,the infrared stray light interference from the sky,local environment and the optical-mechanical structure of telescope will be stronger.Hence,it is the first and most unavoidable task to conduct simulation and evaluation on the impact of infrared stray light in advance and propose the solutions for suppression of stray light in the study of large-scale ground-based solar telescope.In particular,stray light arising from the thermal radiation of the system itself is a distinctive source of stray light in infrared detection systems.Based on the optical system of ground-based solar telescope,this paper studied the infrared stray light caused by thermal radiation of the optical system itself.The main contents are as follows:1.Focusing on the ground-based solar telescope CGST,the finite element analysis software COMSOL was used to simulate the thermal environment of the CGST primary mirror and secondary mirror,and the thermal stability of the ULE mirror embryo and the Zerodur mirror embryo were compared to illustrate the advantages of Zerodur mirror embryo and the necessity of thermal control.2.Comprehensive studies were conducted on the self-thermal radiation stray light of the primary mirror and the secondary mirror in the annular telescope,then the key factors affecting the stray light in the system were found.Using the temperature results simulated by COMSOL,combined with ZEMAX simulation,the stray light generated by thermal radiation at different bands on the primary mirror and secondary mirror surface was quantitatively analyzed under different conditions of working environmental temperatures and different surface emissivity.Further,the results are compared with that of the full-aperture structural reflector.The results indicated that:(1)The thermal radiation from the back of the primary mirror contributed the most to stray light,and it should be emphatically inhibited;(2)The emissivity of the mirror was an important factor affecting the self-thermal radiation and should be kept at a low level as much as possible;(3)The contribution of far-infrared radiation to the system’s own thermal radiation was 1-3 order of magnitudes higher than that of mid-infrared band and near-infrared band;(4)The higher the environment temperature,the stronger the stray light of its own thermal radiation was,so corresponding temperature control measures should be taken for more precise;(5)The annular structure is more advantageous to the self-thermal radiation stray light inhibition than the full-aperture structure.3.Different methods of suppressing the self-thermal radiation stray light for the ground-based solar telescope optical system were introduced from the aspects of surface coating design and temperature control.Basing on the characteristics of CGST’s own thermal stray radiation and analysis,measures on controlling the temperature of CGST primary mirror were given.