title: Diffraction effects in the radiometry of coherent beams.
abstract: High-accuracy radiometry requires an optical beam in which all the light is contained within the radius of the smallest detector to be calibrated. We analyze a common configuration of the optical components used to prepare such a beam and show that diffraction rings are formed in the far field although the irradiance is zero along the limiting aperture's edge. The beam profile is calculated and used to find the radius of the smallest detector that can be calibrated with this beam.
authors.forename: D J
authors.initials: DJ
authors.lastname: Butler
authors.forename: R
authors.initials: R
authors.lastname: Köhler
authors.forename: G W
authors.initials: GW
authors.lastname: Forbes