28Physics Formulary by ir. J.C.A. WeversThe dispersion of a prism is defined by:D=dδdλ=dδdndndλwhere the first factor depends on the shape and the second on the composition of the prism. For the first factorfollows:dδdn=2 sin(12α)cos(12(δmin+α))For visible light usually holdsdn/dλ<0: shorter wavelengths are stronger bent than longer. The refractiveindex in this area can usually be approximated by Cauchy’s formula.6.8DiffractionFraunhofer diffraction occurs far away from the source(s). The Fraunhofer diffraction of light passing throughmultiple slits is described by:I(θ)I0=sin(u)u2·sin(Nv)sin(v)2whereu=πbsin(θ)/λ,v=πdsin(θ)/λ.Nis the number of slits,bthe width of a slit anddthe distancebetween the slits. The maxima in intensity are given bydsin(θ) =kλ.The diffraction through a spherical aperture with radiusais described by:I(θ)I0=J1(kasin(θ))kasin(θ)2The diffraction pattern of a rectangular aperture at distanceRwith lengthain thex
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Sin, Diffraction pattern, Fraunhofer diffraction, n1, Optical axis