Generation of time-varying orbital angular momentum beams with space-time-coding digital metasurface

The recently proposed extreme-ultraviolet beams with time-varying orbital angular momentum (OAM) realized by high-harmonic generation provide extraordinary tools for quantum excitation control and particle manipulation. However, such an approach is not easily scalable to other frequency regimes. We design a space-time-coding digital metasurface operating in the microwave regime to experimentally generate time-varying OAM beams. Due to the flexible programmability of the metasurface, a higher-order twist in the envelope wavefront structure of time-varying OAM beams can be further designed as an additional degree of freedom. The time-varying OAM field patterns are dynamically mapped by developing a two-probe measurement technique. Our approach in combining the programmability of space-time-coding digital metasurfaces and the two-probe measurement technique provides a versatile platform for generating and observing time-varying OAM and other spatiotemporal excitations in general. The proposed time-varying OAM beams have application potentials in particle manipulation, time-division multiplexing, and information encryption.

Automated summary

The recent development of extreme-ultraviolet beams with time-varying orbital angular momentum (OAM) has provided unique tools for quantum excitation control and particle manipulation. However, the scalability of this approach to other frequency regimes is challenging. In this study, we propose a microwave digital metasurface that enables the generation of time-varying OAM beams. By utilizing the programmability of the metasurface, we can design higher-order twist in the envelope wavefront structure of the time-varying OAM beams, offering additional degrees of freedom. Furthermore, we demonstrate the dynamic mapping of the time-varying OAM field patterns using a two-probe measurement technique. This combined approach provides a versatile platform for generating and observing time-varying OAM and other spatiotemporal excitations, with potential applications in particle manipulation, time-division multiplexing, and information encryption.