Random structured spiral beams with spatially varying coherence and their optical radiation forces

We propose what we believe to be a new class of random structured spiral beams with spatially varying coherence. By engineering the second-order statistical properties of light through nonuniform optical coherence design, the three-dimensional intensity evolution of the beam can be flexibly tailored. Both theoretical and experimental results demonstrate that, during focusing and propagation, the beam evolves from an initial Gaussian profile into a spiral structure and subsequently forms a spiral with opposite chirality beyond the focal plane. By adjusting the initial beam parameters, the structural fineness, radial scale, and angular orientation of the spiral can be independently controlled. Further analysis of the optical radiation forces reveals that stable trapping points follow spiral trajectories, forming a three-dimensional trapping channel. These results indicate that spatially varying coherence engineering provides a promising approach for controlled three-dimensional particle transport.