- #1
Nanxie
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Homework Statement
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?
Homework Equations
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 can't seem to solve it using the above equations.
Thanks~ ^^;