Gaussian beam diffraction from radial structures: detailed study on the diffraction from sinusoidal amplitude radial gratings.

Abstract

In this work, we report a comprehensive theoretical investigation on the diffraction of a Gaussian beam from structured radial apertures. In particular, the study of near- and far-field diffraction of a Gaussian beam from an amplitude radial grating having a sinusoidal profile provides new theoretical insights and possible applications. We observe a high self-healing feature at far-field for the Gaussian beam in the diffraction from amplitude radial structures. It is also shown that by increasing the spokes number of the grating, the strength of the self-healing decreases, and reforming of the diffracted pattern into a Gaussian beam occurs at longer propagation distances. The energy flow towards the central lobe of the diffraction pattern and its dependence on the propagation distance are also investigated. In the near-field regime, the diffraction pattern is very similar to the intensity distribution in the central area of the radial carpet beams generated in the diffraction of a plane wave from the same grating. It is shown that by optimally choosing the waist radius of the Gaussian beam, in the near-field regime, it is possible to have a petal-like diffraction pattern, which has been experimentally used in multiple-particle trapping. Compared to radial carpet beams, since in this case there is no energy in the geometric shadow of the radial spokes of the grating, the main part of the power of the incident Gaussian beam is transferred to the main intensity spots of the petal-like pattern, which significantly increases the multi-particle trapping efficiency. We also show that regardless of the grating spokes number, at the far field, the diffraction pattern becomes a Gaussian beam, and its power share reaches 2/3 of the total power passed through the grating.