In this contribution we report an analytical formulation for evaluating along any line, directed towards the geometrical focus, the field diffracted by a rotationally nonsymmetric screen, at any Fresnel number. Our formula consists of two factors. The first factor involves a suitable 1-D Fourier transform of the azimuthally-averaged amplitude transmittance of the screen, around the point where the off-axial line intersects the screen plane. The second factor depends on the inverse distance to the aperture, and it is the responsible for the focal shift effect along the above mentioned straight lines, for low Fresnel numbers.
|