AI 中文总结
该研究提出一种全光超快动态波前整形策略，通过泵浦脉冲调控半导体纳米线超表面的介电常数，实现了皮秒级开关的瞬态波前调控，为全光可重构金属透镜奠定基础。
AI 中文摘要
光学超表面已成为在亚波长尺度上调控光特性的卓越纳米光子平台。通过合理设计其构成的超原子的几何形状和空间排列，可向入射光场施加工程化的相位梯度，从而利用几乎无限的调控自由度对其波前进行整形。然而，超表面一旦制备完成，其光学响应便永久固定。本文提出一种动态调控策略，通过理论预测并实验演示了周期性半导体纳米线超表面中的全光、可逆且超快的波前整形过程。采用强像散飞秒光泵浦脉冲对共振超表面进行非均匀光激发，诱导产生瞬态、空间非均匀的介电常数调制，从而对延迟探测脉冲的波前进行整形。超快成像测量显示，在选定的探测波长下，透射光场发生瞬态散焦，开关时间低于1皮秒。定量数值模拟阐明了散焦机制源于共振超表面未受扰动的光学响应与泵浦诱导的空间介电常数梯度之间的相互作用。本研究建立了一种完全全光且超快的路径，实现了梯度超表面中被动波前整形的动态类似物，为全光可重构金属透镜的发展铺平了道路。
英文摘要
Optical metasurfaces have established themselves as exceptional nanophotonic platforms to control the properties of light at subwavelength scales. By properly designing the geometry and spatial arrangement of their constituent meta-atoms, engineered phase gradients can be imparted to an incoming field, thereby tailoring its wavefront with a virtually unlimited number of control knobs. However, once fabricated, a metasurface has a permanently fixed optical response. Here, we introduce a strategy for dynamic control, by theoretically predicting and experimentally demonstrating all-optical, reversible, and ultrafast wavefront shaping in a periodic semiconductor nanowire metasurface. A strongly astigmatic femtosecond optical pump pulse is used to photoexcite the resonant metasurface non-uniformly, inducing a transient, spatially inhomogeneous permittivity modulation that reshapes the wavefront of a delayed probe pulse. Ultrafast imaging measurements reveal transient defocusing of the transmitted field at selected probe wavelengths, with a switching time below one picosecond. Quantitative numerical modelling elucidates the defocusing mechanism as arising from the interplay between the unperturbed optical response of the resonant metasurface and the pump-induced spatial permittivity gradient. Our work establishes a fully all-optical and ultrafast route to the dynamic analogue of passive wavefront shaping in gradient metasurfaces, paving the way to all-optically reconfigurable metalenses.
