Multidimensional spectroscopy in the visible and infrared spectral ranges has become a powerful technique to retrieve dynamic correlations and couplings in wide-ranging systems by utilizing multiple correlated light-matter interactions. Its extension to the terahertz (THz) regime of the electromagnetic spectrum, where rich material degrees of freedom reside, however, has been progressing slowly. This chapter reviews some of the THz-frequency two-dimensional (2D) spectroscopy techniques and experimental results realized in recent years. Examples include gas molecule rotations, spin precessions in magnetic systems, and liquid molecular dynamics studied by 2D THz or hybrid 2D THz-Raman spectroscopy techniques. The methodology shows promising applications to different THz-frequency degrees of freedom in various chemical systems and processes.

可见光谱和红外光谱范围内的多维光谱学已成为一种强大的技术，可通过利用多个相关的光-质相互作用来检索大范围系统中的动态相关性和耦合。但是，它扩展到电磁频谱的太赫兹（THz）体制，其中存在丰富的材料自由度，但是进展缓慢。本章回顾了一些太赫兹频率二维（2D）光谱技术和近年来实现的实验结果。示例包括气体分子旋转，磁性系统中的自旋进动以及通过2 THz或混合2D THz-拉曼光谱技术研究的液体分子动力学。该方法论显示了在各种化学系统和过程中对不同的太赫兹频率自由度的有希望的应用。