Design method for off-axis aspheric reflective optical system with extremely low aberration and large field of view

This paper proposes a grouping design method based on a combination of spatial ray tracing and aberration correction to construct the initial structure for an off-axis multi-reflective aspheric optical system. This method establishes a mathematical parameter model of the optical system to satisfy the aberration balance and multi-constraint control requirements. The simulated annealing particle swarm algorithm is applied to calculate the initial optical system structure. Finally, an extreme ultraviolet (EUV) lithography projection objective with six-reflective aspheric mirrors is used as an example to verify the reliability and effectiveness of this method. A 0.33 numerical aperture EUV lithographic objective with wavefront error better than 1/70λ(λ=13.5nm) root mean square (RMS) is obtained.