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Abstract
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Measurement of the source size and specifying its effect on the spatial coherence of propagating light are important
for characterizing distant sources such as stars, and imaging with partially coherent light. The common method
for measuring spatial coherence is Young’s two-pinhole experiment. For characterizing spatial coherence along a
line, one needs to change the location of the pinholes over a large number of pairs of points. But it requires many
measurements, which takes significant time. In this paper, we use Fresnel diffraction from a step in reflection to
measure the source width and transverse coherence length. It is shown theoretically and experimentally that these
quantities are determined by specifying the location of minimum visibility on the diffraction pattern.We utilize a
sodium vapor lamp with a variable slit in front of it as an extended one-dimensional incoherent light source. The
measurements are made through recording only one diffraction pattern formed by the step. The study is applicable
in 2D, and one can characterize weak starlight using highly sensitive equipment.
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