Longitudinally tuned OAM vortex beams for advanced particle manipulation

Structured light has become a pivotal tool for optical manipulation, advancing applications from biology to micro-engineering. However, conventional orbital angular momentum (OAM) vortex beams are limited to unidirectional particle rotation in transverse planes, leaving longitudinal control largely undeveloped. Here, we introduce a longitudinally tunable OAM vortex beam (LTOVB) that enables versatile particle dynamics along the optical axis—including stationary trapping, speed modulation, and bidirectional rotation—while maintaining a constant orbital radius. Using vector diffraction modeling and experimental validation, we demonstrate programmable particle manipulation across sequentially tuned OAM segments under tight focusing.