function [ w, s ] = gaussian_focus( w0, s0, f, lambda )
%GAUSSIAN_FOCUS Summary of this function goes here
%   Detailed explanation goes here

zR = pi*w0^2/lambda;
s = f*(1+(s0/f-1)/((s0/f-1)^2+(zR/f)^2));
w = w0/sqrt((1-s0/f)^2+(zR/f)^2);
end