Multi-focus beams with adjustable three-dimensional morphing spatial structure

The beams with axial multiple focusing characteristic have been proven highly valuable in contemporary optics. We propose a new multifocal three-dimensional morphing (M3DM) beam featuring adjustable three-dimensional(3D) morphing spatial structure. By modulating the phase spectrum of a circular Airy beam via a chirped phase and a twisted phase, the circular Airy beam is transformed into a M3DM beam with four focal points. Moreover, the continuous three-dimensional enclosed dark space between two focal points in the middle presents the bottle beam characteristics. The 3D enclosed bottle space and even the focus points exhibit diverse structures by tuning the parameters of the modulated phase. From the energy flow analysis, it is observed that the gradient of energy flow varies with the beam structures. Employing the spatial multiplexing method, an array of M3DM beams is generated, capable of producing four times the number of focal points in 3D space. Furthermore, the dimension and focal position of each M3DM beam element can be independently adjusted with a high degree of freedom. Consequently, the proposed beam with its unique multifocal and self-rotational properties demonstrates promising applications in multiparticle trapping in 3D orientation, bioscience, optical communication, and multiplanar imaging.