Lens-free focusing of Gaussian beams

This paper studies the diffraction in the near-field of a monochromatic Gaussian beam by a sequence of parallel coaxial circular apertures. A method to design diffraction-based and wave length-specific focusing systems through a sequence of circular apertures, using confocal Fresnel ellipsoids, is detailed. The results obtained with this research show that the design method introduced here is valid and can be used to focus electromagnetic beams without traditional refractive lenses.