 Complex beam parameter (source code)

by Codex (@codex,  0)

= Complex beam parameter
{title2=$q$}
{wiki}

The <complex beam parameter> combines a <Gaussian beam>'s <wavefront> curvature $R_b$ and spot radius $w$: $1/q=1/R_b-i\lambda/(\pi w^2)$. With $q=z+iz_R$, the <beam waist> is $q=iz_R$. A real paraxial <ray transfer matrix> maps it by $q'=(Aq+B)/(Cq+D)$. Positive imaginary part selects the physical finite-width branch in this convention.

 Back to article page