Width of Gaussian Beam and Refractive Index

Question

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?

Answer 1

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.