Highly Sensitive Non-linear Probes of Chiral Structure and Dynamics

手性，即物体与其镜像的不重叠性，在自然界中无处不在，是描述自然过程的基础。对于手性分子，这种镜像对称的破坏导致了分子的两个版本，左对映体和右对映体，除了与另一个手性物体（如另一个手性分子或圆偏振光）相互作用时，它们具有相同的化学和物理性质。对手性分子在时域上的响应的兴趣日益增长，促使了最近和正在进行的开发超快速非线性手性技术的努力。本提案旨在发展一种观察手性分子相干激发态动力学的新方法的理论基础。该方法对电子、振动和旋转手性动力学、各种弛豫过程和相干性损失高度敏感。此外，这种方法提供了扩展到非手性分子的可能性，因为它可以诱导“外在”手性。在一些基于非线性光学参数过程的超快光谱中，检测到的信号对底层动力学相干性的灵敏度可能很低，例如，高谐波产生和二维光谱。这是因为这些参数过程导致表征底层动力学的不同路径相互干扰，即使底层动力学是不连贯的。外部手性应该允许人们克服这一限制，并开发出对相干动力学完全敏感的超快测量方案。

Chirality, the non-superposability of an object with its mirror image, is ubiquitous in nature, and fundamental to the description of natural processes. For chiral molecules, this mirror-symmetry breaking leads to two versions of a molecule, the left and right enantiomers, which have identical chemical and physical properties except for when interacting with another chiral object such as another chiral molecule or circularly polarized light. The growing interest in the response of chiral molecules in the time domain has motivated recent and ongoing efforts to develop ultrafast non-linear chiroptical techniques to that aim. This proposal is aimed at developing the theoretical foundations of a novel approach to observing coherent excited state dynamics in chiral molecules. The approach is highly sensitive to electronic, vibrational and rotational chiral dynamics, to various relaxation processes, and to loss of coherence. Additionally, this approach offers the possibility of extension to non-chiral molecules as it can induce 'extrinsic' chirality. The sensitivity of the detected signal to the coherence of the underlying dynamics can be low in a number of ultrafast spectroscopies based on non linear optical parametric processes, such as, e.g. high harmonic generation and 2D spectroscopy. This is because these parametric processes cause the different pathways characterizing the underlying dynamics to interfere even if the underlying dynamics are incoherent. Extrinsic chirality should allow one to overcome this limitation and to develop ultrafast measurement schemes that are exclusively sensitive to coherent dynamics.