Recent content by zebanaqvi

How to prove that energy travels at group velocity and not phase velocity?

Thanks a lot :) Sorry, what I am about to ask might be lame. I have the helmholtz equation, and I want to solution to represent a beam whose phase front is not plane always, whose intensity profile is not uniform across the cross section. What function should I try out? You'll say complex...

I am new to lasers. In the expression for q parameter, 1/q = 1/R - j(λ/πw^2) how did we come to know that w(z) is a measure of decrease in field amplitude E with distance? I can't feel it. Does the gaussian beam itself contract to the minimum diameter? Shouldn't a lens be required for this...