Lecture25 - Fresnel Diffraction Lecture 25 Near field We...

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Lecture 25 Fresnel Diffraction Near field • We can no longer consider only plane wave fronts • The curvature of the wave front depends on how far away the point source is from the obstruction object Fresnel-Kirchhoff Diffraction Integral S r r’ da P dE p = dE o r e ikr O dE o ! E L da = E s r ' " # $ % e ikr ' da = E S rr ' e ik ( r + r ' ) da Integrating over the whole opening E p = E S 1 rr ' e ik ( r + r ') da Ap !! Corrections to the integral obtained Huygens-Fresnel approach The secondary wave is not in phase with the primary wave. The secondary wave does not introduce a wave in backward direction These contributions can be treated properly with EM using Kichhoff’ s scalar diffraction theory E p will obtain the following form E p = E S 1 rr ' e ik ( r + r ') da Ap !! E p = i ! E S " F # ( ) 1 rr ' e ik ( r + r ' ) da A $$ ! F ( ) = F 0 ( ) 2 1 + cos ( ) We only have to solve the integral
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Circular apertures • Divide the aperture into zones of circular symmetry • Each zone is out of phase ( ! ) with the neighboring. • Subdividing the zone gives phases from m
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This note was uploaded on 08/06/2008 for the course PHYS 352 taught by Professor Dierolf during the Fall '04 term at Lehigh University .

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Lecture25 - Fresnel Diffraction Lecture 25 Near field We...

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