The propagation characteristics of a beam diffracted by a circular aperture are investigated. The beam-quality factor <i>M</i><sup>2</sup> defined by an 86.5% power-content radius is given theoretically and experimentally as a function of the truncation ratio. It is found that the theoretical limit of <i>M</i><sup>2</sup> is 2.37 times as great as that of an incident beam as the truncation ratio approaches 0. For a weakly diffracted beam a simple formula giving <i>M</i><sup>2</sup> is derived. Although <i>M</i><sup>2</sup> does not increase much with diffraction, the influence of diffraction should be taken into account in beam brightness.
© 2002 Optical Society of America
(000.4430) General : Numerical approximation and analysis
(030.4070) Coherence and statistical optics : Modes
(050.1220) Diffraction and gratings : Apertures
(260.1960) Physical optics : Diffraction theory
Sho Amano and Takayasu Mochizuki, "Propagation Characteristics of a Diffracted M2 Beam," Appl. Opt. 41, 6325-6331 (2002)