深圳大学电子科学与技术学院 For distance well beyond the Rayleigh range f the radius then increases again as r(z)z, i.e., the gaussian beam becomes essentially like a spherical wave centered at the beam waist. What this means in physical terms is that the center of curvature of the wavefront starts out at -oo for a wavefront right at the beam waist and then moves monotonically inward toward the waist, as the wavefront itself moves outward toward z->o深圳大学电子科学与技术学院 • For distance well beyond the Rayleigh range f the radius then increases again as R(z)z, i.e., the gaussian beam becomes essentially like a spherical wave centered at the beam waist. What this means in physical terms is that the center of curvature of the wavefront starts out at – for a wavefront right at the beam waist, and then moves monotonically inward toward the waist, as the wavefront itself moves outward toward z→ 