Design of pupil off-axis space telescope with freeform surfaces based on the nodal aberration theory

Abstract

Pupil off-axis optical system has the advantages of imaging unobscured and restraining the stray light for the next generation space telescope. However, non-rotationally asymmetric aberrations lead by the pupil off-axis structure becomes the main influencing factor of imaging quality. Since the freeform surface can provide more degrees of freedom for optical design, it is widely used to control the non-rotationally asymmetric aberrations. In order to guide designer optimize the pupil off-axis optical systems with freeform surfaces efficiently, an aberration analysis method for pupil off-axis optical system with Fringe Zernike polynomial freeform surfaces is proposed. The analysis expressions of third-order astigmatism and coma of the pupil off-axis freeform system are deduced. The freeform impacts on aberration nodal properties are analyzed. According to the aberration distribution, a pupil off-axis space telescope freeform optical system is designed by optimizing the Zernike terms pointedly. The effective focal length is 25m, the pupil diameter is 2m. By stitching multi-detectors to realize the field of view (FOV) of 1.2°×1.2°. Because of introducing freeform surfaces, the third-order astigmatism and coma nodes are both moved back to the FOV. Therefore, the asymmetric aberrations lead by pupil off-axis are balanced. The final imaging quality is closed to the diffraction limit, which meets the requirements.