Fresnel Diffraction: Opaque Strip

Jenkins & White's treatment is the best I've found. Below is a sketch from J&W which is in best agreement with what we see with the diffraction pattern from a human hair.

In an undergraduate modern physics laboratory, the diffraction from various objects was observed. When a human hair was tried as the diffracting object with a helium-neon laser, a beautiful diffraction pattern similar to a single slit was observed. But superimposed was a modulation of intensity which looked very much like the rapid undulations of intensity in the slde lobes shown here. We treated the entire lobes as single slit lobes to approximate the single slit behavior.

Cornu spiral
Index

Diffraction concepts

Fresnel diffraction

Reference
Jenkins & White
p. 400
 
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Opaque Circle

An opaque circular disk gives a concentric ring diffraction pattern similar to the circular aperture, but in addition it has a bright spot in the center referred to as either Poisson's spot or Fresnel's spot. It seems more appropriate to name it after Fresnel since he developed the theory. Halliday and Resnick have the best picture of it I have found.

In fact, Poisson strenuously objected to having it named after him because it was observed after an objection he raised to Fresnel's thesis - i.e. that Fresnel's calculation would imply such a bright dot and it hadn't been seen. This initiated a search for it and it was quickly found.

Index

Diffraction concepts

Fresnel diffraction

Reference
Halliday, Resnick,Walker
Ch 37
 
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