Design method for an off-axis reflective anamorphic optical system with aberration balance and constraint control

This paper proposes a design method for an off-axis reflective anamorphic optical system (ORAOS). This method first applies vector aberration theory to establish a mathematical model to balance the aberration of an ORAOS. It then builds the error function of structural parameters and constraints through spatial ray tracing and grouping design. Next, it introduces automatic adjustment of weight factors for dynamic balance of aberrations and constraints. A particle swarm simulated annealing algorithm is used to iteratively calculate the initial structure of the ORAOS. Finally, we use an extreme ultraviolet (EUV) lithographic projection objective with off-axis six-reflective anamorphic mirrors (beta(x) = 1/4, beta(y) = 1/8) as an example to verify the effectiveness of this method. We obtain an EUV lithographic anamorphic objective with a numerical aperture of 0.55 and a root mean square wavefront error better than 1/30 lambda (I >> = 13.5 nm). (C) 2021 Optical Society of America