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Niles
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Homework Statement
Consider a cylindrical piece of material of a constant thickness d and radius r = a, but made out of a material with position-dependent index of refraction. How must the index of refraction vary with radial distance r such that the cylindrical piece act as a lens with a focal length of f. Assume d << a, i.e., a thin lens.
The Attempt at a Solution
Ok, first I remind myself that light follows the path, where the optical path length is stationary. So I write
[tex]
\Gamma = \int {n\left( {r,\phi ,z} \right)} \,rdrd\phi dz.
[/tex]
I can integrate dz and dφ out, since we only want to look at the r-dependence. Now, I need to find dGamma/dr = 0, but that just gives me n(r)=0, which is clearly wrong. Can you give me a hint?Niles.
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