first: emission from a plane interface, which covers the whole x,y plane second: emission from parts of the plane (apetures, circular and rectangular) In the rectangular case: one edge length very long, often infinite; Both cases - caused (or explained) by interference of "wavelets"coming from different positions of an opening

Important mathematical trick: Weyl's expansion of spherical wave(let)

Fresnel cases: quadratic dependence on the distance from the normal (from the "axis" or "the edge") Fraunhofer cases: large distance; the quadratic term becomes negligible, the linear is important

( note that the plots on further slides go only to corresponds to N=2.0; and for N=2 we get darker region in the middle ) Remember that the circular case contains the Bessel function J1(x) where x is quadratic function of the radial distance

( note )

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