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I know that in free space, the width of a Gaussian beam can be written as $W=W_0\sqrt{1+(\frac{z}{z_0})^{2}}$. However, I was wondering if it was possible to express this width as a function of refractive index instead (since I don't believe a Gaussian beam originating in say, glass, will diverge in the same manner as one in air). Anyone have any ideas?

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up vote 3 down vote accepted

Yes, and the formula you already have still works. Take z to be the optical path length: refractive index n times physical distance. A Gaussian beam in glass diverges in exactly the same way as in free space, only 'squeezed' in the z direction by a factor of n.

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Looks good. Could you take a look at my other question:…, which is related to this one? – John Roberts Oct 1 '12 at 18:38

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