Active optical alignment of off-axis telescopes based on nodal aberration theory

Our paper mainly separates the specific aberration contributions of third-order astigmatism and third-order coma from the total aberration fields, on the framework of the modified nodal aberration theory (NAT), for the perturbed off-axis telescope. Based on the derived aberration functions, two alignment models for the same off-axis two-mirror telescope are established and compared. Among them, one is based on third-order NAT, the other is based on fifth-order NAT. By comparison, it is found that the calculated perturbations based on fifth-order NAT are more accurate. It illustrates that third-order astigmatism and third-order coma contributed from fifth-order aberrations can't be neglected in the alignment process. Then the fifth-order NAT is used for the alignment of off-axis three-mirror telescopes. After simulation, it is found that the perturbed off-axis three-mirror telescope can be perfectly aligned as well. To further demonstrate the application of the alignment method based on fifth-order NAT (simplified as NAT method), Monte-Carlo simulations for both offaxis two-mirror telescope and off-axis three-mirror telescope are conducted in the end. Meantime, a comparison between NAT method and sensitivity table method is also conducted. It is proven that the computation accuracy of NAT method is much higher, especially in poor conditions. (C) 2016 Optical Society of America