The statistical description of light fields emitted from thermal sources enables us to completely take into account all effects of source dimensions, the spectral composition of the radiation, and the geometrical characteristics of any interference phenomena. Again we assume that the light source consists of a huge number of elementary (atomic) sources, and in the present chapter we shall see, how effects of these sources can be found from simple considerations regarding their statistical properties. However, the existence of any correlation of the fields in a light beam is of interest in itself, because it is the field correlation that allows a stationary superposition of amplitudes at a point of observation to become observable. In other words, the observation of all diffraction and interference phenomena, produced by a superposition of light waves, is only possible since a field correlation exists.
KeywordsCorrelation Function Interference Pattern Spectral Distribution Interference Fringe Spatial Mode
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