Implications of diffraction theory for aperture transmission in optical radiometry

Theoretical results for the total flux transmitted by a circular aperture are reviewed for four theories of propagation: rigorous theory, Kirchhoff diffraction theory, Fresnel diffraction theory, and geometrical optics. Curves are given which indicate, for a desired accuracy, the wavelength and aperture size at which the theories diverge. The implications for flux calculations and area measurements are discussed. Measurements of the transmission of a medium-sized aperture support the validity of the Kirchhoff and rigorous theories over the Fresnel and geometrical theories at optical wavelengths, but are unable to determine decisively the most accurate theory.