Atoms and Light: Interactions pp 161-180 | Cite as

# Optical Coherence and Counting Statistics

## Abstract

The coherence of a light field can be domonstrated by the phenomenon of interference. In the classical experiment of Thomas Young in 1801 the coherence was induced by arranging that the light diffracted by a fine slit should illuminate two parallel slits which then acted as two coherent sources. In the more modern version of the experiment a laser beam illuminates the two slits; the transverse coherence across the laser beam creates two coherent sources. The temporal coherence between the two sources can be displayed by superimposing the field *E*(*t*) from one slit with the field from the other at a different time *E*(*t* + *τ*). This is achieved by observing the intensity at points that are at different distances, *s* _{1} and s_{2}, from the two slits so that one is superimposing the light fields from two different times *t* _{2} − *t* _{1} = *τ* = (*s* _{1} − *s* _{2})/*c*; see Fig. 18. The field at the observation point *P* at time *t*′ originates from the slit *s* _{1} at time *t* _{1} = *t*′ − *s* _{1}/*c* = *t*; and originates from the slit *s* _{2} at a later time *t* _{2} = *t*′ − *s* _{2}/ *c* = *t* + *τ*.

## Keywords

Light Field Coherence Function Coherence Time Coherent Light Classical Source## Preview

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