Dark spot in Fraunhofer diffraction

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    Diffraction Fraunhofer
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Discussion Overview

The discussion revolves around the unexpected appearance of dark spots in the Fraunhofer diffraction patterns produced by a narrow slit aperture. Participants explore potential causes for these anomalies, questioning the applicability of established principles such as Babinet's principle and the relevance of the diffraction regime being analyzed.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant reports observing dark spots in the diffraction pattern that are not predicted by the Fourier transform of the aperture.
  • Another participant questions the meaning of "near the edges of the slits," suggesting that this might indicate a transition to Fresnel diffraction rather than remaining in the Fraunhofer regime.
  • The original poster clarifies that "near the edges of the slits" refers to the incident beam being close to the top or bottom of the slit aperture, providing specific dimensions of the slit.
  • Some participants express uncertainty regarding the cause of the observed dark spots.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the cause of the dark spots, and multiple viewpoints regarding the interpretation of the diffraction regime and the slit geometry remain unresolved.

Contextual Notes

The discussion highlights potential limitations in understanding the diffraction behavior due to assumptions about the diffraction regime and the specific geometry of the aperture.

thepopasmurf
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Hi, I've been doing Fraunhofer diffraction and I have been getting dark spots in the middle if my patterns, not predicted by the Fourier transform of the aperture. I don't think it's babinets principle and effect is stronger near the edges of the slits. Any ideas? Thanks
 
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Not sure what would cause that. What do you mean by "near the edges of the slits"? Near the slits would correspond to Fresnel (near field) diffraction, not Fraunhofer diffraction. What is your specific slit or aperture geometry?
 
What do you mean by "near the edges of the slits"?

I mean when incident beam is near the top or bottom of the slit aperture.
The aperture in question is a narrow slit, around 100 microns wide (i think, that's off the top of my head) and perhaps 2mm or 3mm high.
 
Weird, not sure what would cause that.
 

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