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Fraunhofer Diffraction Proving 
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#1
Sep1504, 02:53 AM

P: 79

I am to prove that in
y = R * m * (wavelength) / a where y is the distance between two minima, a is the width of the slit, R is the length between the screen and the slit grating, and m is an integer which is the order of the minima. I know I have to use the paraxial approximation where tan x is approximately sin x which is approx. x, but I can't seem to apply it. When I refer to my textbooks, they state that y is the difference between the central maximum and the first minimum when m=1. Is this applicable bet. two minima as well? 


#2
Sep1504, 07:20 PM

Sci Advisor
P: 1,474

Start with the condition for constructive interferance;
dsin(theta) = m(lambda) Then apply the small angle approximation. It is quite simple. Your textbook is referring to y as the difference between the first maximum and the centre of the pattern, which is equivalent (within the small angle approximation) to the distance between successive minima. Claude. 


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