The phenomenon of bending of light from the corners or edges of aperture or obstacles and departure of true rectilinear path of light is diffraction of light. It is due to the super position secondary wavelets generated from single wave front.
Types of Diffraction
1. Fresnel diffraction: If the source of light and screen is finite distance from the slit, then this type of diffraction is Fresnel diffraction. No lenses are needed to converge the light at slit and screen. The incident wave front on slit is spherical or cylindrical.
2. Fraunhofer diffraction: If the source of light and screen is infinite distance from the slit, then this type of diffraction is Fraunhofer diffraction. Two lenses are used to converge the light at slit and screen. The incident wave front on slit is plane wave front.
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