Superposition, interference and diffraction of light waves

For the sake of simplicity, here we will only treat the interaction between two individual, hnearly polarized light waves, described hyE =A cos k r — co t- -(p ) 

Although a very general treatment is possible, let us assume here that the two waves have the same frequency, i.e. CO = coi = C02- In this case, constructive (adding of amplitudes) and destructive (subtraction of amplitudes) interference is observed at the location of interaction, depending on the total phase difference arising from the combined path difference and the initial phases between the two waves. The composite amplitude averaged over an oscillation period is constant with time, leading to the intensity distribution at the location of wave interference  

For a more rigorous treatment of wave superposition and interference, the reader is referred to general textbooks on optics (see the Further Reading Ust). 

An important parameter in diffraction theory is the so-called Fresnel number of a diffracting system  

Fraunhofer diffraction, for which F = 1, deals with the limiting cases where the tight approaching the diffracting object is (nearly) parallel (plane-wave illumination) and (nearly) monochromatic, and where the image plane is at a distance that is large compared with the size of the diffracting object (the so-called far-field case). 

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