Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
J Chem Phys. 2018 May 21;148(19):194201. doi: 10.1063/1.5030402.
A fundamental goal of chemical physics is an understanding of microscopic interactions in liquids at and away from equilibrium. In principle, this microscopic information is accessible by high-order and high-dimensionality nonlinear optical measurements. Unfortunately, the time required to execute such experiments increases exponentially with the dimensionality, while the signal decreases exponentially with the order of the nonlinearity. Recently, we demonstrated a non-uniform acquisition method based on radial sampling of the time-domain signal [W. O. Hutson , J. Phys. Chem. Lett. , 1034 (2018)]. The four-dimensional spectrum was then reconstructed by filtered back-projection using an inverse Radon transform. Here, we demonstrate an alternative reconstruction method based on the statistical analysis of different back-projected spectra which results in a dramatic increase in sensitivity and at least a 100-fold increase in dynamic range compared to conventional uniform sampling and Fourier reconstruction. These results demonstrate that alternative sampling and reconstruction methods enable applications of increasingly high-order and high-dimensionality methods toward deeper insights into the vibronic structure of liquids.
化学物理学的一个基本目标是理解处于平衡和非平衡状态下液体中的微观相互作用。原则上，通过高阶和高维非线性光学测量可以获得这种微观信息。不幸的是，执行此类实验所需的时间随维度呈指数增长，而信号随非线性阶数呈指数衰减。最近，我们展示了一种基于时域信号的径向采样的非均匀采集方法[W. O. Hutson，J. Phys. Chem. Lett.，1034（2018）]。然后通过使用逆 Radon 变换的滤波反投影来重建四维光谱。在这里，我们展示了一种基于不同反投影光谱的统计分析的替代重建方法，与传统的均匀采样和傅里叶重建相比，该方法的灵敏度显著提高，动态范围至少提高了 100 倍。这些结果表明，替代的采样和重建方法使得越来越高阶和高维的方法能够应用于深入了解液体的振动结构。
