Parameters of a Gaussian Laser Beam. A 1-mW He-Ne laser produces a Gaussian beam at a wavelength of A = 633 nm with a spot size 2W = 0.1 mm. (a) Determine the angular divergence of the beam, its depth of focus, and its diameter at 2 = 3.5 x 10 km (approximately the distance to the moon). (b) What is the radius of curvature of the wavefront at z = 0, x = 20, and z = 2z0? (c) What is the optical intensity (in W/cm) at the beam center (z = 0, p = 0) and at the axial point z = zo? Compare this with the intensity at zo of a 100-W spherical wave produced by a small isotropically emitting light source located at z = 0.