Propagation analysis of self-convergent beam width and characterization of hard-edge diffracted beams

For a laser beam diffracted by a hard-edge aperture, propagation of the beam width, defined by the second-order moment of its irradiance distribution truncated according to the self-convergent-width criterion, obeys the familiar hyperbolic law. It is demonstrated numerically that, with the self-convergent-width approach, the beam-propagation parameters for three beam types (Gaussian, Hermite-Gaussian, and flattened Gaussian) diffracted by hard-edge apertures can be determined with the second-moment-based procedure that is recommended by the present draft standard only for unapertured laser beams.