Analysis of diffraction from the occulter edges of a giant externally occulted solar coronagraph

A technique is described for the calculation of the intensity of the light diffracted by the occulter of an externally occulted solar coronagraph. This technique can be applied to an occulter of generic shape, but the attention is here focused on a specific application; that is, the case of a giant space solar coronagraph, in which the occulter is located at 100 m from the telescope aperture. By means of the code developed, it has been possible to simulate the effects of various shapes of the occulter edge with the aim of analyzing in detail the best apodization for the coronagraph. The results obtained show that an occulter with a circular serrated edge allows a remarkable reduction of the amount of diffracted light on the coronagraph’s entrance aperture with respect to a simpler circular disk case