(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Hello, I'm really confused about this one, =(

Suppose I have a guassian beam that is colliminated (beam expanded) and then suppose i let it passed through a lens to focus it.

Given an initial waist and focal length of the lens. How can i find the waist (or half width) at the focus?

2. Relevant equations

3. The attempt at a solution

There's an approximation using the formula above

w(z)=(lambda*z)/(pi*w0)

where w0 is the waist at focus and z is the distance from it, so if i let z=f i can solve for w0

but this only works if z >> pi(w0)/lambda

how about for the case when z is small (or the focal length is small), i cant seem to solve it using the above equations.

Thanks~ ^^;

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# Homework Help: Gaussian Beam focused using a lens

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