Approximation of the encircled energy function for the far-field diffraction of a plane light wave by planar complex-shaped apertures

A method for approximating the encircled energy in a definite solid angle in the Fraunhofer region by the simulation of the optical transfer function derivative is proposed. The selection of free model parameters allow one to obtain a valid expansion of the encircled energy at the origin of the angular coordinate and at infinity, providing a good approximation in the intermediate domain.