Generation of multi-focus abruptly autofocusing beams with adjustable focus characteristics

Generation controllable optical chain using an optical pen

An aperiodic snake-like optical chain has been proposed and generated by using an optical pen technique, whose numbers and positions of focal points are controllable. Moreover, by introducing a fan phase together with a twisted phase into the optical pen technique, a self-rotation optical chain can be obtained; meanwhile, it transforms the bright optical chain into a twisted optical chain with a rotating hollow region in a three-dimensional (3D) space. The properties of the rotatable focal points and the variable diameters of cross-sectional intensities during the propagation of the optical chain are demonstrated in the experimental results. Consequently, this research framework can be applied in the techniques such as deep multiplexing and rotation angle multiplexing while also enabling the realization of multiple capture sites and more intricate manipulations.

Generating multi-focus beams with a spatial non-uniform coherence structure

We introduce a class of structured light beams, named multi-focus beams, which exhibit self-focusing at multiple propagation distances. We show that the proposed beams not only have the ability to produce multiple longitudinal focal spots, but also that the number, intensity, and position of the foci can be controlled by adjusting the initial beam parameters. Furthermore, we demonstrate that these beams still exhibit self-focusing in the shadow of an obstacle. We have experimentally generated such beams and the results are consistent with the theoretical predictions. Our studies may find application where fine control of the longitudinal spectral density is needed, such as longitudinal optical trapping and manipulation of multiple particles, and transparent material cutting.

Multi-focus autofocusing circular hyperbolic umbilic beams

We propose and demonstrate a type of multi-focus autofocusing beams, circular hyperbolic umbilic beams (CHUBs), based on the double-active variable caustics in catastrophe theory. The mathematical form is more general compared to circular Airy, Pearcey and swallowtail beams. The CHUBs can generate multi-focus at its optical axis, while the on-axis intensity fluctuates up to two orders of magnitude that of the maximum intensity in the initial plane. Using the concept of topographic prominence, we quantify the autofocusing ability. We construct the criteria for selecting the effective foci, and then explore the influence of related parameters. Our findings suggest that the CHUBs could be a suitable tool for multi-particle manipulation, optical tweezers, optical lattices and related applications.