A Gaussian beam is coming out of a laser. Assume λ = 6000 Å and that at z = 0, the beam wi...

A Gaussian beam is coming out of a laser. Assume λ = 6000 Å and that at z = 0, the beam width is 1 mm and the phase front is plane. After traversing 10 m through vacuum what will be (a) the beam width and (b) the radius of curvature of the phase front.