Galactic-form spinning beams

Creating a structured transverse-intensity distribution that undergoes axial rotation during propagation while preserving its overall shape remains a major challenge, as achieving a stable, continuous, and substantial rotation across the entire beam cross-section has thus far proven elusive. Here, we introduce a class of intensity-rotating structured beams generated by diffracting a plane wave through a purely amplitude-based spiral-like structure composed of curved radial spokes, periodic in both radial and azimuthal directions. The diffraction patterns form concentric rings with petal-like intensity spots, whose number and spacing are set by the spoke count. Spoke curvature, L, induces relative azimuthal shifts between rings, producing a global rotation around the optical axis during propagation. Increasing L by an order of magnitude yields measurable rotations over 10−2 of the initial propagation length, enabling faster rotations at shorter distances. Simultaneously, the beam divergence decreases, evolving toward a quasi-non-diffractive regime. The spots trace spiral trajectories reminiscent of galactic arms, inspiring the term galactic-form spinning beams. Phase analysis shows vortex-like azimuthal variations with topological charge equal to the spoke number. Numerical and experimental results confirm these dynamics, offering opportunities for structured-light applications. Intensity-rotating beams are a class of structured beams that can potentially enable advanced optical manipulation techniques, as well as applications in free-space optical communication and high-resolution imaging, but their exploration has remained mostly theoretical. The authors demonstrate galactic-form spinning beams, i.e a stable, intensity-rotating beam whose dynamics and divergence can be precisely controlled.