Symmetric sub-diffraction focusing via hybrid Airy-superimposed vector beams

To overcome the conventional diffraction limit in optical systems, we propose a class of hybrid Airy-superimposed vector beams (HASVBs) and investigate their tightly-focusing properties. These HASVBs are formed by orthogonally superposing an inverse circular Airy beam and a circular Airy beam. Using the Richards-Wolf vector diffraction theory, we numerically demonstrate that HASVBs can generate a symmetric sub-diffraction focal spot, breaking the classical diffraction limit in both transverse dimensions. By adjusting the initial phase difference between two components, the focal-spot shape can be tuned periodically from elliptical to circular symmetry. Furthermore, the influence of key beam parameters-the main-ring radius, scaling factor, and decay factor-on the focal-spot size is systematically analyzed. For a given optical system with a certain numerical aperture, optimal sub-diffraction focal spots can be achieved by appropriately choosing the main-ring radius and scaling factor. Moreover, the longitudinal intensity patterns reveal that our design produces a needle-like profile near the focal region. The result has promising potential for applications in super-resolution imaging, direct laser writing, and optical manipulation.