AI 中文总结
研究基于光学涡旋驱动的高次谐波产生，通过少周期涡旋光束驱动ZnO晶体中的HHG，发现谐波辐射拓扑电荷受晶体反演对称性破缺和载波包络相位影响，可通过CEP控制调整，为波形控制的结构化阿秒光源研究提供了新方向。
AI 中文摘要
由光学涡旋驱动的高次谐波产生（HHG）是在不同光谱区域产生结构化光的有力途径。根据缩放定律\(l_q = q\times l\)，非线性过程将轨道角动量（OAM）从驱动场转移到发射的谐波，这是旋转不变性和角动量守恒的结果。我们表明，在少周期脉冲的情况下，在有限光谱窗口内检测到的谐波辐射的拓扑电荷（TC）不再仅由该缩放定律固定，而是由晶体反演对称性破缺和载波包络相位（CEP）敏感的亚周期电子动力学之间的相互作用决定。通过用中心波长为3.2~μm的少周期（约1.5个周期）涡旋光束驱动ZnO晶体中的HHG，我们观察到测量的TC变得强烈依赖于CEP，在相邻整数值之间切换，但仅当反演对称性被打破且谐波发射对CEP敏感时才会发生。当任何一个条件被去除时，TC切换消失。数值分析表明，TC切换源于CEP控制的光谱权重在光谱重叠谐波阶之间的重新分布，这改变了检测窗口内的主导OAM通道。这些结果将CEP确定为调整高次谐波辐射拓扑结构的一个自由度，指向波形控制的结构化阿秒光源。
英文摘要
High-order harmonic generation (HHG) driven by optical vortices is a powerful route to produce structured light in different spectral regions. The nonlinear process transfers orbital angular momentum (OAM) from the driving field to the emitted harmonics according to the scaling law $l_q = q\times l$, a consequence of the rotational invariance and angular momentum conservation. Here, we show that, in the regime of few-cycle pulses, the topological charge (TC) of the harmonic radiation detected within a finite spectral window is no longer fixed by this scaling law alone, but is governed by the interplay between broken crystal inversion symmetry and carrier-envelope phase (CEP)-sensitive sub-cycle electron dynamics. By driving HHG in a ZnO crystal with few-cycle ($\approx 1.5$ cycles) vortex beams centered at 3.2~$μ$m, we observed that the measured TC becomes strongly CEP-dependent, switching between adjacent integer values, but only when the inversion symmetry is broken and the harmonic emission is CEP-sensitive. The TC switching vanishes when either condition is removed. Numerical analysis reveals that the TC switching originates from a CEP-controlled redistribution of spectral weight among spectrally overlapping harmonic orders, which changes the dominant OAM channel within the detection window. These results identify the CEP as a degree of freedom for tailoring the topological structure of high-harmonic radiation, pointing toward waveform-controlled structured attosecond light sources.
