Propagation dynamics of a dual-ring perfect vortex beam with configurable parameters in a gradient-index medium

In this paper, the propagation characteristics of the dual-ring perfect vortex beam (DR-PVB) with full manipulation of its amplitude, radius, beam width, and topological charge (TC) for each ring in a gradient-index (GRIN) medium are systematically investigated. The influences of TCs l_o and l_i, ring radii w_o and w_i, full widths at half-maximum (FWHM) d_o and d_i, and the factor of GRIN medium b on beam evolution, especially on the focal field pattern, are analyzed. DR-PVB experiences periodic focusing and produces multilayered focal structures. By tuning beam and medium parameters, the number of bright spots and the peak intensity at the focal plane, and the focusing period can be flexibly controlled, respectively. l_o and l_i jointly regulate field intensity distributions and rotation directions. Proper ring radii and FWHM raise focal peak intensity. Reducing b shortens the focusing period and strengthens focal light intensity. Moreover, radiation force calculations demonstrate that DR-PVBs enable multi-position particle trapping and improved trapping stiffness via multimodal transverse and smooth axial optical forces. This work provides a feasible strategy for flexibly engineering vortex light fields in GRIN media and promotes their applications in optical manipulation.