Galactic-form spinning beams

We present a new class of intensity-rotating structured beams generated by diffracting a plane wave through a pure amplitude spiral-like structure (SLS) composed of curved radial spokes, periodic in both radial and azimuthal directions. The resulting diffraction pattern consists of concentric rings with petal-like intensity spots, whose number and spacing are determined by the spoke count. Due to the spoke curvature, adjacent rings exhibit a relative azimuthal shift, causing the overall pattern to rotate around the optical axis during propagation, with angular speed proportional to the curvature. Simultaneously, the beam’s divergence reduces, evolving toward a quasi-non-diffractive regime. The high-intensity spots in the first ring follow helical trajectories resembling the grooves of a drill—thus termed “optical drill.” Across all rings, the spots trace spiral paths akin to galactic arms, inspiring the name “galactic-form spinning beams.” Phase analysis shows each ring carries vortex-like azimuthal phase variations with topological charge equal to the spoke number, while radial phase steps depend on curvature. Without curvature, the pattern resembles a radial carpet beam with net-zero charge. Experimental and numerical results confirm these dynamics. Such beams offer potential for optical trapping, enabling combined axial and rotational manipulation of particles along spiral trajectories.