Understanding Fraunhofer Diffraction: Classical vs. Quantum Interpretation

In summary: All light is diffracted when it goes near a slit. However, the amount of diffraction depends on the wavelength of the light.
  • #1
Ezio3.1415
159
1
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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  • #2
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
 
  • #3
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.
 
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  • #4
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?"
 
  • #5
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.
 
  • #6
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?
 
  • #7
Ezio3.1415 said:
btw what does quantum mechanics say abt diffraction?

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

1. What is the difference between classical and quantum interpretation of Fraunhofer diffraction?

The classical interpretation of Fraunhofer diffraction describes the diffraction pattern as the result of light waves passing through a narrow slit and producing a pattern of bright and dark fringes. The quantum interpretation, on the other hand, explains the diffraction pattern as the result of the wave-like nature of particles, such as photons, passing through the slit and interfering with each other.

2. Is one interpretation more accurate than the other?

Both interpretations are valid and have been supported by experimental evidence. However, the quantum interpretation is considered to be more accurate as it can explain phenomena that cannot be explained by classical theories, such as the photoelectric effect.

3. Can Fraunhofer diffraction occur with other types of waves besides light waves?

Yes, Fraunhofer diffraction can occur with any type of wave, including sound waves and water waves. The diffraction pattern will depend on the wavelength of the wave and the size of the diffracting object.

4. How is Fraunhofer diffraction used in practical applications?

Fraunhofer diffraction is commonly used in spectroscopy to analyze the properties of materials and in the design of optical instruments, such as telescopes and microscopes. It is also used in the production of holograms and in the study of the atomic and molecular structure of materials.

5. Are there any limitations to the classical or quantum interpretation of Fraunhofer diffraction?

The classical interpretation has limitations when describing the behavior of very small particles, such as electrons, which exhibit wave-like behavior. The quantum interpretation also has limitations, as it cannot fully explain the behavior of larger objects, such as macroscopic objects. However, both interpretations have been successful in explaining and predicting the diffraction patterns observed in various experiments.

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