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![[Figure 14]](ge5117fig14mag.jpg)
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Figure 14
Young's experiment for creating an interference pattern in which two apertures are illuminated with quasi-monochromatic radiation from a temporally and spatially extended incoherent source (the waves from the two source points shown are emitted independently of one another with a random phase difference). In this two-dimensional illustration, the radiation is emitted as circular waves from each point on a line. The distances between source and apertures and between apertures and detection line are great enough that the Fraunhofer or far-field limit is a valid approximation for describing the scattering. At the location of the apertures A1 and A2, the circular wavefronts are nearly planar. Any single-aperture diffraction that might occur and modulate the two-slit interference pattern plotted on the far right-hand side of the figure is neglected since it is not relevant to the arguments made concerning the role of the mutual coherence function and fringe visibility discussed in the text (this is equivalent to both single-aperture widths approaching zero). The red and green patterns of intensity plotted on the right correspond to two point sources, one at the origin S0 and the other off the horizontal axis of symmetry at S1, respectively. The blue curve results upon adding these two single-source-point intensity distributions together. Because of the translational offset between the two single-point patterns, a reduced `fringe' visibility or diminished instrumental resolution results. |
![[Figure 14]](ge5117fig14.jpg)
 | JOURNAL OF APPLIED CRYSTALLOGRAPHY |
ISSN: 1600-5767
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