Calculations of M-squared values for clipped focused Gaussian beams using vector diffraction theory

Vector diffraction theory is applied to apertured Gaussian laser beam propagation. The computational model developed treats the light field as a 6-component vector electromagnetic wave. None of the commonly employed approximations are assumed (i.e., ray optics, scalar field approximations, paraxial approximations, wavelengths much smaller than longitudinal or tangential distances, etc.) A conductive circular aperture is placed in a converging Gaussian laser beam. Light field distributions beyond the aperture and within the focal region are investigated as a function of the clipping ratio (the ratio of the aperture radius to the Gaussian beam width in the diffraction plane.) The effects of a variety of clipping ratios on the field's maximum intensity and the beam's M-squared value are investigated.