Study on alignment technology of off-axis four-mirror optical systems based on vector aberration theory

The image quality of reflective optical systems is influenced strongly when the position of each mirror changed compared to the theoretical design state. Since multiple degrees of freedom in reflective optical system and the interaction between each mirror coupled, which makes it difficult to separate the misalignment of each mirror accurately. By now, vector wave-front aberration theory has been used to computer-aided alignment of two-mirror and three-mirror optical systems widely, however, due to actual engineering demands, optical systems with more than three mirrors have been designed, which greatly increases the difficulty of installation and alignment. At present, there are still few researches on this aspect. Based on vector wave aberration theory, the aberration shift vector of each element in four-mirror optical systems with off-axis field is derived by using paraxial ray trace equation of the optical axis ray and the principle ray, then the misalignment model of the four-mirror optical systems with shifted field is established in detail. The model can accurately calculate the misalignment of optical elements, which greatly promotes the high-precision alignment of complex reflective optical systems. And the perturbed off-axis four-mirror telescope can be perfectly aligned in terms of the vector aberration theory. This greatly facilitates the optical design technology of complex reflective optical systems in some way.