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What I cannot understand and what my textbook does not mention is where the 0.61 part comes from. How is this derived and what is the significance of 0.61? In your equation if you take nuclear diameter $D=2R$ Then your relation looks like $D\sin\theta = 1.22 \lambda$ If one wishes to resolve two objects separated by a distance $D$, one can use ...

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It is not possible to write a closed form equation for the Fresnel diffraction pattern. Usually one will use the Cornu spiral to evaluate problems like this. The Cornu spiral is a graphical tool that maps the phase / amplitude contribution of a infinitesimal element of the aperture. (image by R. Nave, from http://hyperphysics.phy-astr.gsu.edu/hbase/...

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Note I am the OP The geometric angle of deviation is given by: $$\theta_{dg}=\theta \frac{u}{|v|}$$ $$=\theta\left| 1-\frac{u}{f}\right|$$ If we let $u=f+\Delta$ then: $$\theta_{dg}=\theta\frac{ |\Delta|}{f}$$ Now taking $\Delta$ to be small we can assume the angular deviation due to diffraction is given by: $$\theta_{dd}=\frac{1.22 \lambda}{D}$$ $$=\frac{1.... 0 In X-ray crystal structure analysis the useful wavelength of approx. one angstrom is used (one can get X-rays in that range from different targets) which is available from x-ray sources. The above wave length is of the order of length of covalent bond and the radius of single atoms. Therefore the X-ray scattered/diffracted data can be more useful. ... 2 This is really just a geometry problem since we can not use Fraunhofer approximation in general. The solution depends on what you mean by "width" of the central maximum. If you take it to be the distance between the two adjacent minima (full width) then the solution is:$$z_{fresnel} = \frac{a^2}{4 \lambda} - \frac{\lambda}{4} Alternatively the full ...

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It looks like a diffraction pattern from the pixels of the screen. In a different SE question, the pattern was four horizontal and vertical "rays" consisting of finely spaced peaks, rather than the wide spacing here and the angles that differ from 90 degrees. If you measure the apparent angle between the first diffraction peaks (the ones at the edge of the ...

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