Probing molecular chirality and chiral dynamics using High Harmonic generation

我们项目的主要目标是开发对分子手性（包括其结构和动力学）敏感的新方法。我们的目标包括解决和控制分子中的多电子手性动力学在其自然的，亚飞秒的时间尺度。到目前为止，这种超快的手性反应时间尺度仍然隐藏在实验中。所提出的方法是基于高谐波产生的气体的随机取向的分子（手性HHG，cHHG）。它的关键部分是应用定制的强脉冲来诱导、增强和操纵手性响应。手性是生命物质的基本属性，对其功能至关重要。分子的左右对映异构体具有相同的化学和物理性质，除非它们与另一个手性物体（如手性光）相互作用。在旋转各向同性介质中的手旋光辨别的传统方法是线性光谱技术，其测量左和右对映异构体对手性（例如，圆偏振）光的光学响应的差异。在这些技术中，手旋光效应来自于光诱导的电偶极跃迁和磁偶极跃迁之间的相互作用。光-物质相互作用中的磁效应一般很弱。这导致弱的手旋光响应，通常比例如光吸收小四到六个数量级。手性响应的弱点给时间分辨测量带来了挑战，对增强手性响应的不断努力使得在非常具有挑战性的气相研究中取得了显着的进展。 最灵敏的技术之一是光电子圆二色性光谱，PECD，它预示着手性光学鉴别中的“偶极革命”：不使用手性光的手性鉴别。 几种新的方法遵循这一显着的突破，纯粹在电偶极子近似下工作，包括对映体敏感的微波检测，光激发圆二色性（PXCD）和光激发诱导的光电子圆二色性（PXECD）。PXCD和PXECD的概念是在该提案的第一阶段开发的，涉及超快激发和手性电子或振动动力学的探测。 我们的理论提供了一个统一的和简单的描述所有偶极近似为基础的技术，并澄清了机制，使手性歧视没有手性脉冲。有了这些知识，我们准备迈出关键的新一步：我们建议将“偶极革命”带到手性HHG。通过新的cHHGd方法，我们的目标是实现高手性二色性值-所有基于偶极的技术的标志，同时还能够以比现有最先进技术好两个数量级的时间分辨率对潜在的手性动力学进行精确成像。

The main objective of our project is to develop new methods sensitive to molecular chirality, both its structure and dynamics. Our goals include resolving and controlling multielectron chiral dynamics in molecules at its natural, sub-femtosecond time-scale. So far, this ultrafast time-scale in chiral response has remained hidden in experiments. The proposed method is based on high harmonic generation from a gas of randomly oriented molecules (chiral HHG, cHHG). Its key component is the application of tailored intense pulses to induce, enhance and manipulate the chiral response.Chirality is a basic property of living matter, crucial for its function. Left and right enantiomers of molecules have identical chemical and physical properties unless they interact with another chiral object, such as chiral light. Traditional methods of chiroptical discrimination in rotationally isotropic media are linear spectroscopic techniques, which measure the difference of the optical response of left and right enantiomers to chiral (e.g. circularly polarized) light. In these techniques, the chiroptical effects arise from the interplay between the light-induced electric- and magnetic-dipole transitions. The magnetic effects in light-matter interaction are generally very weak. This results in a weak chiroptical response, often four to six orders of magnitude smaller than e.g. light absorption. The weakness of the chiral response poses challenges for time-resolved measurements.Constant efforts towards the enhancement of the chiral response have led to a remarkable recent progress in very challenging gas-phase studies. One of the most sensitive techniques is photoelectron circular dichroism spectroscopy, PECD, which heralded the "dipole revolution" in chiro-optical discrimination: chiral discrimination without using chiral light. Several new methods followed this remarkable breakthrough, working purely in electric dipole approximation, including enantio-sensitive microwave detection, photoexcitation circular dichroism (PXCD) and photoexcitation induced photoelectron circular dichroism (PXECD) . The concepts of PXCD and PXECD were developed in phase I of this proposal and involve ultrafast excitation and probing of chiral electronic or vibrational dynamics. Our theory provides a unified and simple description of all dipole-approximation based techniques and clarifies the mechanisms enabling chiral discrimination without chiral pulses. With this knowledge we are ready for the key new step: We propose to bring the "dipole revolution" to chiral HHG. With the new cHHGd method we aim to achieve high values of chiral dichroism – the hallmark of all dipole-based techniques, while also being able to simultanelously image the underlying chiral dynamics with the time resolution that is two orders of magnitude better than the available state-of-the art techniques.