Twisted Light Beam from a Gradient-Based Inverse-Designed Metasurface

Optical vortex beams, characterized by helical wavefronts and orbital angular momentum (OAM), exhibit a phase singularity that forms a distinctive doughnut-shaped intensity profile. However, conventional observation methods often struggle to directly visualize their twisting behavior, limiting the ability to fully exploit spatial beam evolution in applications such as optical manipulation and three-dimensional structured light–matter interaction. In this work, we numerically and experimentally demonstrate a gradient-based inverse-design methodology to engineer metasurface capable of generating twisted light beams without predefined OAM or complex forward design processes. Our optimized metalens achieves precise triple-helical focusing, with focal spots consistently rotating by 40° clockwise across design focal planes and maintaining a stable radius of 2 μm. This approach offers significant potential for novel modes of optical tweezers and light-mater interaction, where controlled spatial rotation—distinct from traditional OAM-based beams—may enable new particle manipulation strategies, as well as for applications in imaging, lithography, and depth sensing.