Fraunhofer diffraction (Diffraction by a slit of infinite depth)
In optics, the Fraunhofer diffraction equation is used to model the diffraction of waves when the diffraction pattern is viewed at a long distance from the diffracting object, and also when it is viewed at the focal plane of an imaging lens. In contrast, the diffraction pattern created near the object, in the near field region, is given by the Fresnel diffraction equation.
For a a monochromatic plane wave at normal incidence and a diffraction by a slit of infinite depth, the width of the central band in the diffraction pattern can be calculated by the wavewidth, the distance that the diffracted light is viewed and the width of the slit.( If W < λ, the intensity of the diffracted light does not fall to zero, and if D << λ, the diffracted wave is cylindrical).
|df||Width of the central band in the diffraction pattern (mm)|
|z||Distance that the diffracted light is viewed (mm)|
|W||Width of the slit (mm)|