Analysis The Infrared Stray Light Of Optical System Of Ground Solar Telescope

For the mid-infrared and far-infrared band are the last untapped solar physics observation windows, it contains many unknown observation opportunities. However, there is a great difference on detecting object and background noise of infrared solar observation comparing with visible light detection. So it becomes a problem which needs to be solved urgently and also a key technology to analyze and evaluate the influences of infrared stray light for the system, taking effective measures for suppression of stray light and improving the signal-noise ratio of the infrared astronomical observation during the research and development of the infrared solar telescope.In this paper, the main works about the infrared stray light of the optical system for ground-based solar telescope are mainly as follows:(1) Giving a comprehensive analysis of the stray light sources for the ground-based solar telescope. According to the source of infrared stray light, it can be divided into three categories:the outside stray light, the thermal radiation stray light and non-imaging path stray light. We also have analyzed the propagation path of these three sources, determined the theoretical model and analysis methods.(2) For the outside stray light, the background noise on the image plane caused by infrared radiation of the sun and atmosphere in the three atmosphere windows are simulated. The results show that the outside stray light is the main source of infrared noise especially in the near-infrared band.(3) About the internal thermal radiation stray light caused by high temperature resulting from the ambient temperature and solar radiation, we mainly simulated the thermal radiation stray light of the large size of primary mirror and secondary mirror, further the thermal radiation stray light of the ring structure and the full aperture structure mirror is compared and analyzed. The results show that the thermal radiation stray light of the ring structure is more and more significant with the infrared window moving to long wavelength, this value of middle and far infrared is improved2-3orders of magnitude than near infrared. While the primary mirror’s value is also2-3higher orders than the secondary mirror’s.Comparing different structure of mirror, the thermal radiation stray light of ring primary mirror and secondary mirror are about2-3times lower than that of the full aperture structure’s, respectively. It is clear that the ring structure is more favorable for the suppression of the thermal radiation of the system.(4) The diffraction and scattering are mainly discussed for the stray light of non-imaging path. The edge of the field stop produces more significant infrared diffraction stray light than that of the visible light band, and it becomes stronger with increasing of the incident light intensity, which forms background of stray light with great influence on infrared imaging system. For the stray light of surface scattering, through simulation of the different scattering model, the results show that the mirror scattering has little effect on the infrared stray light contribution.(5) Comprehensive analysis of various infrared stray light levels of ground-based solar telescope, the crucial infrared stray light sources of the telescope are obtained.In1-3μm range, the outside stray light is the key sources, in3-5μm range, three sources are all the key sources; and in8-12μm range, the thermal radiation of stray light is higher than other two kinds of sources nearly an order of magnitude, which becomes the focus of control. Meanwhile, the suppression measures for the key infrared stray light sources are discussed.