Diffraction analysis of multiple-disk occulters in external coronagraphs based on uniform boundary wave diffraction theory.

Occulters with multiple-disk structure are commonly used for mitigating the diffraction light from specific incident angles in external coronagraphs. In the design phase of coronagraphs, it is of great importance to calculate the diffraction propagation of the occulters with high accuracy and high efficiency. In this paper, an analytical method is proposed for the diffraction analysis of multiple-disk occulters based on uniform boundary wave (BDW) diffraction theory. First, an analytical propagator with Fresnel functions is derived for single-disk case, of which the accuracy and efficiency are demonstrated by a numerical example. Then it is proved that the propagator in multiple-disk case was just the iterative use of the single-disk one when neglecting the gradient diffraction term. The analytical propagator presents much improvement on simplification and efficiency compared to former numerical propagators, and hence, is of great significance to future external coronagraph design and analysis.