Generation and application of controlled needle-like focuses in circular Swallowtail beams

This paper delves into the mechanism underlying the formation of needle-like focus in circular Swallowtail beams and examines its potential applications in particle manipulation dynamics. Through the integration of the cross-phase and the chirp factor, we present an innovative design for a circular Swallowtail beam with a needle-like focus (NFCSB). This beam generates two mutually perpendicular needle-like foci at distinct positions during propagation. Through thorough theoretical analysis and experimental verification, we explore the propagation characteristics of the NFCSB in free space and investigate the effective generation mechanism and the control of the needle-like focus. Our findings indicate that the intensity, the length, and the position of the needle-like focus can be precisely controlled by adjusting the initial parameters. Additionally, the NFCSB demonstrates high efficiency in capturing Rayleigh particles and guiding them to align linearly along the light intensity distribution. These results not only advance the modulation of circular Swallowtail beams and the formation of special focal spots, but also offer new opportunities for practical applications, such as optical capturing and precision manufacturing.