A street lamp has a diffusing glass globe of diameter

PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Coherence and statistical optics · Coherence and statistical optics

What an Instrument Can See, Ch Spatial coherence and the van Cittert-Zernike theorem

Problem

0.40\,\text{m}

, modelled as a uniform incoherent disc source, viewed from a distance of

100\,\text{m}

. Take the light as quasi-monochromatic at

\lambda = 550\,\text{nm}

. ((a)) Estimate the transverse coherence radius (the separation of the first zero of

|\mu_{12}|

) in the plane of an observer

100\,\text{m}

away. ((b)) A typical human pupil has diameter about

3\,\text{mm}

. Estimate how many coherence patches (of the size found in part (a)) fit across the pupil area, and use this to say whether light entering the eye from the lamp should be treated as spatially coherent or incoherent.

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