Understanding Fraunhofer Diffraction: Classical vs. Quantum Interpretation

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Discussion Overview

The discussion centers around the phenomenon of Fraunhofer diffraction, particularly in the context of single slit diffraction, exploring both classical and quantum interpretations. Participants examine the nature of light as it interacts with a slit, questioning the roles of different parts of the wavefront and the implications of diffraction theory.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that only light near the slit is diffracted, questioning whether light passing through the middle contributes to the central maximum.
  • Others argue that the electromagnetic wave cannot be divided in such a manner, asserting that the diffraction pattern results from the wave interfering with itself rather than light being diffracted off the edges of the slit.
  • There is a challenge to the interpretation that diffraction occurs only at the edges, with some suggesting that all parts of the slit contribute to the diffraction pattern.
  • A participant expresses confusion regarding the explanation of minima and maxima in the context of diffraction, seeking clarification on how these features arise.
  • Some participants acknowledge the Huygens–Fresnel principle as a framework for understanding diffraction, emphasizing the need to view light as a wave rather than as rays.
  • There is a mention of quantum mechanics and its relation to diffraction, with a participant noting that while the mathematics differs, the outcomes remain consistent with classical interpretations.

Areas of Agreement / Disagreement

The discussion contains multiple competing views, particularly regarding the nature of diffraction and the contributions of different parts of the wavefront. There is no consensus on the interpretations presented.

Contextual Notes

Participants express uncertainty about the implications of their interpretations, particularly concerning the roles of various rays and the definitions of diffraction in classical versus quantum contexts.

Who May Find This Useful

This discussion may be of interest to those studying optics, wave theory, or quantum mechanics, particularly in relation to diffraction phenomena.

Ezio3.1415
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In single slit fraunhofer diffraction, only the light which goes near the slit is diffracted... If it goes just through the middle it will not be... If the slit is really small would light be diffracted even if it goes through middle?And do all light waves that go near the slit diffract? Does all light that goes through the middle go undiffracted and contribute to central maximum?

What would be the classical and quantum interpretation of this question?
 
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The EM wave cannot be divided into parts that "go through the middle" or not. When focused down to a spot, the resulting airy disk is the result of the EM wave interfering with itself. Contrary to popular belief, no light is being "diffracted off the edges". The pattern of the airy disk is a result of missing part of the wavefront. For example, a larger aperture in a camera or telescope allows more of the EM wave in which results in more of the wave interfering with itself, with the end result being a smaller airy disk. I cannot explain it well. See the following link for a MUCH more detailed look: http://www.telescope-optics.net/diffraction_image.htm
 
Ezio3.1415 said:
In single slit fraunhofer diffraction, only the light which goes near the slit is diffracted... If it goes just through the middle it will not be...

Where did you get this from? I think you must have misinterpreted something that you read. Each point in the diffraction pattern receives light from all parts of the slit.
 
Last edited:
Drakkith Thank you very much for the link... But what do you mean by 'no light is being "diffracted off the edges'... If there's no diffraction then why the pattern is like it is? You said for the missing wave fronts... Then is the proof wrong where the pattern is explained using

'some rays.who change their direction at an angle.then we pair them & explain minima.'
Though I didn't see the explanation for maxima there?

Jtbell I was asking what happens for which rays? But I should've left these lines and asked the ques... "do all light waves that go near the slit diffract? Does all light that goes through the middle go undiffracted and contribute to central maximum?"
 
Ezio3.1415 said:
Drakkith Thank you very much for the link... But what do you mean by 'no light is being "diffracted off the edges'... If there's no diffraction then why the pattern is like it is? You said for the missing wave fronts... Then is the proof wrong where the pattern is explained using

I imagine you are thinking of diffraction like photons bouncing off the sides of the slit. This is not true at all. Light is an EM wave. When it passes through a slit and emerges on the other side it wants to expand outwards from the slit. Per the Huygens–Fresnel principle, we can consider the wave to consist of an infinite amount of waves of infinitesimal size. (Not wavelengths) These infinitesimal waves all interfere with each other as they propagate, with the resulting diffraction pattern depending on the size of the slit and the wavelength of the light.

See here: http://en.wikipedia.org/wiki/Huygens–Fresnel_principle
http://en.wikipedia.org/wiki/Diffraction_formalism

'some rays.who change their direction at an angle.then we pair them & explain minima.'
Though I didn't see the explanation for maxima there?

Do not think of light as "rays" or you WILL be confused. Rays do not explain diffraction and interference.

Jtbell I was asking what happens for which rays? But I should've left these lines and asked the ques... "do all light waves that go near the slit diffract? Does all light that goes through the middle go undiffracted and contribute to central maximum?"

The entire wavefront is affected by going through the slit.
 
Thank you...

I knew the huygen's principle and the explanation given by wave theory of light... Trying to think about photon in it was a wrong approach... However,I should say waves that hit the screen at an angle(angle that is created from their origin with the axis)...

btw what does quantum mechanics say abt diffraction?
 
Ezio3.1415 said:
btw what does quantum mechanics say abt diffraction?

The math is different, but the end result is the same.
 

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