Polarization engineering and characterization of coherent high-frequency radiation are essential to investigate and control the symmetry properties of light–matter interaction phenomena at their most fundamental scales. This work demonstrates that polarization control and characterization of high-harmonic generation provides an excellent ellipsometry tool that can fully retrieve both the amplitude and phase of a strong-field-driven dipole response. The polarization control of high-harmonic generation is realized by a transient nonlinear dipole grating coherently induced by two noncollinear counterrotating laser fields. By adjusting the ellipticity of the two driving pulses simultaneously, the polarization state of every high-harmonic order can be tuned from linear to highly elliptical, and it is fully characterized through an energy-resolved extreme ultraviolet polarimeter. From the analysis of the polarization state, the ellipsometry indicated that both the amplitude and phase of the high-harmonic dipole scale rapidly with the driving laser field for higher-order harmonics, and, especially, for gases with a small ionization potential. Our experimental results were corroborated by theoretical simulations. Our findings revealed a novel high-harmonic ellipsometry technique that can be used for the next generation of high-harmonic spectroscopy and attosecond metrology studies because of its ability to provide single-digit attosecond accuracy. Our work also paves the way to precisely quantify the strong-field dynamics of fundamental processes associated with the transfer of energy and angular momentum between electron/spin systems and the symmetry-dependent properties of molecules and materials.

中文翻译：

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高阶非线性偶极响应，具有极紫外椭偏仪的特征

极化工程和相干高频辐射的表征对于在最基本的尺度上研究和控制光-物质相互作用现象的对称性至关重要。这项工作表明，高谐波产生的极化控制和表征提供了一种出色的椭圆仪工具，该工具可以完全恢复强场驱动偶极子响应的幅度和相位。高谐波产生的偏振控制是通过由两个非共线反向旋转激光场相干感应的瞬态非线性偶极光栅实现的。通过同时调整两个驱动脉冲的椭圆度，可以将每个高谐波阶次的极化状态从线性调整为高度椭圆，并通过能量分解的极端紫外旋光仪进行了全面表征。从偏振态的分析，椭圆偏振法表明，高谐波偶极子的振幅和相位都随着激光场的驱动而迅速缩放，以产生高次谐波，尤其是对于电离势较小的气体。理论模拟证实了我们的实验结果。我们的发现揭示了一种新颖的高谐波椭偏测量技术，该技术可提供下一代阿托秒准确度，因此可用于下一代高谐波光谱学和阿秒计量学研究。