Transient birefringence of liquids induced by terahertz electric-field torque on permanent molecular dipoles.
Transient birefringence of liquids induced by terahertz electric-field torque on permanent molecular dipoles.
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DOI：
10.1038/ncomms14963
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发表时间：
2017-04-10
影响因子：
16.6
通讯作者：
Kampfrath T
中科院分区：
文献类型：
--
作者：
Sajadi M;Wolf M;Kampfrath T
低频分子集体运动对液体中的化学反应和结构弛豫有重要影响。到目前为止，这些模式主要是通过非共振光脉冲间接访问的。在这里，我们提供的证据表明，强烈的太赫兹（THz）脉冲可以共振激发重取向的非质子和强极性液体通过耦合到永久分子的偶极矩的librational模式。我们观察到一个显着增强的响应，因为瞬态光学双折射是高达一个数量级高于获得光激发。依赖于频率的测量和一个简单的分析模型表明，增强产生共振驱动的振动和它们的耦合到重定向运动，由泵场和/或笼平移模式的协助。我们的研究结果开辟了应用的道路，如有效的分子排列，增强瞬态克尔信号和系统的共振非线性太赫兹光谱的分子间模式在液体中的耦合。液体中的低频结构动力学及其潜在的相互作用是复杂且具有挑战性的。在这里，Sajadi等人使用强太赫兹场通过将场耦合到其永久分子偶极矩来直接询问极性液体中的分子间模式。
Collective low-frequency molecular motions have large impact on chemical reactions and structural relaxation in liquids. So far, these modes have mostly been accessed indirectly by off-resonant optical pulses. Here, we provide evidence that intense terahertz (THz) pulses can resonantly excite reorientational-librational modes of aprotic and strongly polar liquids through coupling to the permanent molecular dipole moments. We observe a significantly enhanced response because the transient optical birefringence is up to an order of magnitude higher than obtained with optical excitation. Frequency-dependent measurements and a simple analytical model indicate that the enhancement arises from resonantly driven librations and their coupling to reorientational motion, assisted by the pump field and/or a cage translational mode. Our results open up the path to applications such as efficient molecular alignment, enhanced transient Kerr signals and systematic resonant nonlinear THz spectroscopy of the coupling between intermolecular modes in liquids. Low-frequency structural dynamics in liquids and their underlying interactions are complex and challenging to resolve. Here, Sajadi et al. use intense terahertz fields to directly interrogate intermolecular modes in polar liquids by coupling the fields to their permanent molecular dipole moments.