When a Gaussian beam with complex amplitude U(r) = |A|eiϕ is transmitted through a thin lens, What happens to both |A| and ϕ?
1) Both |A| and ϕ are modified by the lens
2) Only |A| is modified by the lens
3) Only ϕ is modified by the lens
4) Neither |A| nor ϕ is modified by the lens
5) The answer depends on whether we are close to or far from the beam waist
