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Fraunhofer diffraction 
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#1
Nov1612, 04:54 AM

P: 159

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? 


#2
Nov1612, 08:59 PM

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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.telescopeoptics.net/diffraction_image.htm



#3
Nov1612, 10:30 PM

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#4
Nov1712, 06:15 PM

P: 159

Fraunhofer diffraction
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
Nov1712, 08:15 PM

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


#6
Nov1912, 07:32 PM

P: 159

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? 


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