Light fields behind microstructures: study of the Babinet-principle in the Fresnel regime

The Babinet’s principle is a general theorem that holds for electromagnetic waves and is often applied to diffraction of light. Diffraction pattern of a body and that of the complement body are compared and the sum of both radiation patterns must be the same as for an unobstructed beam. In most cases of practical applications light fields are measured by recording the intensity and is limited by a numerical aperture smaller than one. In our contribution we study amplitude and phase behind amplitude structures. We demonstrate using the example of Talbot images what happens in experiments that try to use the Babinet’s principle to understand diffraction patterns for small periodic structures. Of particular interest is the regime close to the structure, the so-called Fresnel diffraction regime. We present results of simulation and measurement to show the impact of a limited numerical aperture