The Fraunhofer Diffraction formula where we've dropped the subscripts, 0 and 1, E(x,y) = const if a plane wave Aperture function We can write this result in terms of the off-axis k-vector components: k x = kx 1 /z and k y = ky 1 /z kzkz kyky kxkx  x = k x /k = x 1 /z and  y = k y /k = y 1 /z and: or:
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