A Cryogenic Research Reflective Off-axis Collimator Vacuum

Space remote detection technology continues to evolve and progress, that brings about increasing requirements of space optical systems. Off-axis reflective collimators with large-aperture and high-quality have become one of the focus of the study. In this paper, the optical design of a low-temperature vacuum off-axis reflective collimator, the temperature compensation method under low temperature, low temperature thermal deformation of the system, processing and testing technology of the aspherical mirror, the alignment technique and image quality under cooling conditions are researched.According to the design specifications of the collimator with Φ380mm diameter and6m focal length, the off-axis R-C structure is proposed to choose. The initial structure of the system is calculated. The design result is optimized by Zemax software. The RMS value of wavefront aberration in the center field is better than0.02λ, and RMS value in the axis field is better than0.25λ.The instrument works under100K-330K cryogenic vacuum environment. Reverse temperature compensation mode using invar steel and stainless steel, is presented. The temperature distribution and thermal deformation of the systerm, the primary mirror and steering mirror after4-days temperature reduction, is analyzed by Patran sofyware. Under conditions of low temperature150K, the temperature is evenly distributed, the mirror deformation is less than λ, and the image quality of the system is stable.Taking account of surface shape requirements of the primary mirror with Φ390mm diameter and380mm off-axis distance, the knife-edge method and Offner compensation are choosed for fabrication and testing. Finally, the RMS value is better than λ/30.Using dynamic interferometer and auto-collimation method, the installation of the system at normal temperature and pressure adjustment is completed. The outgoing wavefront aberration of the system is better than λ/10. How the positional relationship between the primary and secondary mirrors effects on the image quality of the system in the alignment process, is analyzed. Real-time monitoring temperature dropping from20℃to-110℃, the outgoing wavefront aberration of the system is better than0.25λ, that achieves the design requirements.