Ultrafast dynamic mid-infrared beam steering via hot-electron modulation in graphene metasurfaces

Ultrafast dynamic wavefront control is pivotal for advancing photonics applications in LiDAR, high-resolution imaging, and quantum information processing. Conventional wavefront control techniques, such as mechanical beam steering and liquid-crystal-based modulators, are limited by slow response times and bulky configurations, making them unsuitable for high-speed, on-chip applications. In this work, we propose a graphene-based phase-gradient metasurface that leverages hot-electron dynamics for tunable, ultrafast wavefront control in the mid-infrared regime. By precisely modulating the electron temperature in graphene with femtosecond laser pulses, our device achieves real-time beam steering with a maximum reflection angle shift of 21° within 104 fs, as well as dual-focal length switching. The device demonstrates high reflectivity, continuous 2π phase modulation, and an achromatic response over a substantial bandwidth, making it a robust solution for high-speed optical encoding and adaptive optics. This graphene-based platform provides a compact, reconfigurable solution that overcomes the limitations of traditional and emerging approaches, establishing a foundation for next-generation integrated photonics systems.