Braiding of vortices in superpositions of Bessel–Gaussian beams for creation of high-contrast intensity structures

Abstract

Bessel vortices are well-known for their long focal region and the unique property of carrying angular momentum. These characteristics are desired in applications such as laser micromachining, optical trapping, and imaging. Interference of several non-diffracting vortical beams results in light fields with complex intensity distribution structure — many single charged positive and negative vortices appear and experience complex dynamics under propagation. The trajectory of single-charged vortices creates braided structures as they move, annihilate, or are created during propagation. This influences the dynamics of the high intensity regions of the combined beam: high-contrast symmetrical structures are created in the intensity profile. We demonstrate an experimental generation of such complex fields by superimposing several higher-order vortical Bessel beams. We introduce different cone angles of the interfering beams and study modifications of the resulting beam profile. We analyze the vortical structure of the combined beam, track its evolution, and observe the creation of complex high-contrast structures. We implement a convenient technique for generating superimposed higher-order Bessel beams of different spatial frequencies and topologies using diffractive phase masks. We employ a spatial light modulator to experimentally realize these structured fields and to verify theoretical and numerical predictions.