Generating Helical Polymorphic Beams Using Dielectric Metasurfaces

ABSTRACT Helix‐shaped polymorphic beams are structured optical fields formed by the coherent superposition of Bessel beams with carefully selected orders. Their intensity maxima trace a helical trajectory during propagation. By engineering the transverse phase and amplitude, these beams generate optical forces for particle propulsion and trapping. Upon interaction with particles, the resulting axial forces can be either attractive or repulsive, enabling operation in tractor‐beam or pushing‐beam regimes. Their generation has traditionally relied on bulky and expensive spatial light modulators, whereas metasurfaces provide a compact and cost‐effective alternative. While metasurfaces have been used to generate two‐component solenoid beams, a specific subset of helix‐shaped polymorphic beams using phase‐only modulation, metasurface‐based generation of more general helix‐shaped polymorphic beams remains unexplored. Here, we demonstrate the generation of general helical polymorphic beams using metasurfaces for the first time, to the best of our knowledge. Two approaches are used. First, a geometric‐phase‐based complex‐amplitude approach enables simultaneous amplitude and phase control, providing flexibility for complex field engineering. By incorporating intermediate‐plane holography via back‐propagation of the target field, we achieve a 30% relative improvement in experimental efficiency. Second, we demonstrate beam generation using a phase‐only encoding approach, simplifying metasurface fabrication using techniques commonly used with phase‐only spatial light modulators.