Axial Irradiance Distribution Throughout the Whole Space Behind an Annular Aperture: Comments

We comment on the recent paper by Harvey and Krywonos [Appl. Opt. 41, 3790 -3795 (2002) , in which ]approximate irradiance calculations along the axis of a circular aperture illuminated by a plane wave are performed. As the starting point of their calculations, an approximated version (valid for z >>(lambda)) of the RayleighSommerfeld diffraction integral is used. They based their numerical conclusions on a misleading "near field criterion, " which guides the readers to the wrong idea that their calculations are valid even for the very near field behind the aperture. Their ideas are not original; the exact calculations of diffracted fields behind a circular aperture have been known for 40 years [J. Opt. Soc. 51, 1050 -1054 (1961) .]