Joyce T, Jaron-Becker A
Opt Lett. 2020 Apr 1;45(7):1954-1957. doi: 10.1364/OL.388758.
High harmonic spectroscopy utilizes the extremely nonlinear optical process of high-order harmonic generation (HHG) to measure complex attosecond-scale dynamics within the emitting atom or molecule subject to a strong laser field. However, it can be difficult to compare theory and experiment, since the dynamics under investigation are often very sensitive to the laser intensity, which inevitably varies over the Gaussian profile of a typical laser beam. This discrepancy would usually be resolved by so-called macroscopic HHG simulations, but such methods almost always use a simplified model of the internal dynamics of the molecule, which is not necessarily applicable for high harmonic spectroscopy. In this Letter, we extend the existing framework of macroscopic HHG so that high-accuracy ab initio calculations can be used as the microscopic input. This new (to the best of our knowledge) approach is applied to a recent theoretical prediction involving the HHG spectra of open-shell molecules undergoing nonadiabatic dynamics. We demonstrate that the predicted features in the HHG spectrum unambiguously survive macroscopic response calculations, and furthermore they exhibit a nontrivial angular pattern in the far field.
高谐波光谱学利用高次谐波产生（HHG）这一极其非线性的光学过程，来测量处于强激光场中的发射原子或分子内复杂的阿秒级动力学。然而，理论与实验的比较可能会很困难，因为所研究的动力学通常对激光强度非常敏感，而在典型激光束的高斯分布范围内，激光强度不可避免地会发生变化。这种差异通常会通过所谓的宏观HHG模拟来解决，但此类方法几乎总是使用分子内部动力学的简化模型，而这不一定适用于高谐波光谱学。在本信函中，我们扩展了现有的宏观HHG框架，以便能够将高精度的从头计算用作微观输入。这种新方法（据我们所知）被应用于最近一项涉及经历非绝热动力学的开壳层分子的HHG光谱的理论预测。我们证明，HHG光谱中预测的特征在宏观响应计算中明确地保留下来，而且它们在远场呈现出非平凡的角向模式。
