Field spread of a diffracted Gaussian beam through a circular aperture

The behavior of the diffraction field of a Gaussian beam through an aperture depends on incidence conditions and aperture radius. The field spread in the Fraunhofer region varies with the curvature of the equiphase surface of the incident beam as well as the ratio of the aperture radius to the spot size. The divergence angle obtained from the field spread is considered and an approximation method to the diffracted beam by one Gaussian beam is proposed. And the effect of curvature of the incident equiphase surface is also discussed.