气相中非线性二维太赫兹光子回波和转动光谱
Nonlinear two-dimensional terahertz photon echo and rotational spectroscopy in the gas phase
摘要：
超快二维光谱学利用相关的多个光-物质相互作用来检索可能隐藏在线性光谱下的动态特征。它的延伸到太赫兹制度的电磁波谱，其中的丰富多样的材料自由度驻留，仍然是一个实验的挑战。在这里，我们报告超快二维太赫兹光谱的气相分子转子在室温下。利用时延太赫兹脉冲对，我们观察到光子回波和其他非线性信号所产生的分子偶极取向诱导的三个太赫兹场偶极子相互作用。非线性时域取向信号被映射到二维旋转谱的频域，揭示了J态分辨的非线性旋转动力学。该方法可以直接观察相关的旋转跃迁，并可能揭示在地面电子和振动状态的旋转耦合和弛豫途径。
英文摘要：
Ultrafast two-dimensional spectroscopy utilizes correlated multiple light-matter interactions for retrieving dynamic features that may otherwise be hidden under the linear spectrum. Its extension to the terahertz regime of the electromagnetic spectrum, where a rich variety of material degrees of freedom reside, remains an experimental challenge. Here we report ultrafast two-dimensional terahertz spectroscopy of gas-phase molecular rotors at room temperature. Using time-delayed terahertz pulse pairs, we observe photon echoes and other nonlinear signals resulting from molecular dipole orientation induced by three terahertz field-dipole interactions. The nonlinear time-domain orientation signals are mapped into the frequency domain in two-dimensional rotational spectra which reveal J-state-resolved nonlinear rotational dynamics. The approach enables direct observation of correlated rotational transitions and may reveal rotational coupling and relaxation pathways in the ground electronic and vibrational state.
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