Sufficient conditions for the application of the Fresnel approximation of the two-dimensional Kirchhoff diffraction formula are derived for spatially band-limited input signals diffracted by a slit. The method used is an extension of the one given by Papoulis, who derives conditions only for input signals that are sufficiently smooth. For band-limited input signals, the Fresnel region can have an upper limit for the axial extent, depending on the maximum frequency in the input signal.
© 1975 Optical Society of America
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