Focusing properties of the double-vortex beams through a high numerical-aperture objective

We study the focusing properties of the double-vortex beams through a high numerical-aperture objective based on the vectorial Debye theory. We investigate the double-vortex beams composing of two rings, and each ring carries different orbital angular momentum (OAM). It is shown that the total intensity distributions in the focal region are of double-ring structure, and by adjusting certain parameters, the shape of double-ring can be changed. The tight focusing of the double-vortex beams may find applications in micro-particle trapping, manipulation, material processing, etc.

► Focusing of a double-vortex beam (DVB) through a high NA objective is studied.
► Intensity distribution of the DVB is found to be of double-ring structure.
► Each ring of the DVB carries different orbital angular momentum.
► Tight focusing of the DVBs may find many applications in optical spanner, etc.