Control of symmetry breaking in multiphoton ionization of chiral molecules

对称性破缺是自然科学中一个反复出现的主题，其学科领域从粒子物理学的基本问题到手性分子在化学、生物学和医学中的应用。光与物质相互作用中对称性破缺的一个特别有趣的例子是光电子圆二色性（PECD）。PECD描述了光电子角分布沿光传播方向的前向/后向（轴向）不对称性，所述光电子角分布沿着光传播方向由用圆偏振光在气相中的随机取向的手性分子的光电离产生。PECD非常适合于研究与手性相关的轻物质相互作用的对称性破缺，因为与传统的圆二色性相比，观察到的不对称性更明显许多数量级。最近，我们已经证明了使用飞秒激光源的PECD测量通过共振增强多光子电离的小有机手性分子。随着能够产生少周期激光脉冲的新型超快光源的出现，通过脉冲的载波包络相位（CEP）稳定，垂直于光传播方向（横向）的额外对称性破缺变得可行。这个项目的主要目标是证明在CEP稳定的定制强光场与手性分子的相互作用中的横向对称性破缺。我们计划研究CEP稳定化对PECD的影响，并进行补充参数研究，以揭示潜在的量子动力学。在实验中，我们将采用CEP稳定的超短脉冲与定制的偏振态和宽范围的激发波长作为先进的光源电离和断层重建的三维光电子角分布的速度图成像检测。通过将CEP稳定化与脉冲剪裁技术相结合，可以实现对手性分子多光子电离对称性破缺的前所未有的控制。

Symmetry breaking is a recurring theme in the natural sciences with subject areas ranging from fundamental problems in particle physics to applications of chiral molecules in chemistry, biology and medicine. A particularly intriguing example of symmetry breaking in the interaction of light and matter is the Photoelectron Circular Dichroism (PECD). PECD describes a forward / backward (axial) asymmetry in the photoelectron angular distribution along the light propagation direction arising from photoionization of randomly oriented chiral molecules in the gas phase with circularly polarized light. The PECD is ideally suited to study symmetry breaking of light matter interactions associated with chirality because the observed asymmetries are many orders of magnitude more pronounced compared to the conventional circular dichroism. Recently, we have demonstrated the use of femtosecond laser sources for PECD measurements via resonance enhanced multiphoton ionization of small organic chiral molecules. With the advent of novel ultrafast light sources capable of producing few-cycle laser pulses, an additional symmetry breaking perpendicular to the light propagation direction (lateral) has become feasible by Carrier Envelope Phase (CEP) stabilization of the pulse. The main objective of this project is a demonstration of lateral symmetry breaking in the interaction of CEP-stabilized tailored intense light fields with chiral molecules. We plan to investigate the implications of CEP stabilization on the PECD and to carry out complementing parameter studies to reveal the underlying quantum dynamics. In the experiment, we will employ CEP-stabilized ultrashort pulses with tailored polarization state and a broad range of excitation wavelengths as an advanced light source for ionization and tomographic reconstruction of three-dimensional photoelectron angular distributions by velocity map imaging for detection. By combining CEP-stabilization with pulse tailoring techniques, an unprecedented degree of control on symmetry breaking in multiphoton ionization of chiral molecules will be attained.