Control of symmetry breaking in multiphoton ionization of chiral molecules

对称性破缺是自然科学中反复出现的主题，学科领域从粒子物理的基本问题到手性分子在化学、生物和医学中的应用。光和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(PECD)。PECD描述了气相中随机取向的手性分子与圆偏振光的光致电离引起的光电子角分布沿光传播方向的前向/后向(轴)不对称。PECD非常适合于研究与手性有关的轻物质相互作用的对称性破缺，因为观察到的不对称性比传统的圆二向色性要明显许多个数量级。最近，我们已经展示了利用飞秒激光光源通过共振增强的有机手性小分子的多光子电离来测量PECD。随着能够产生短周期激光脉冲的新型超快光源的出现，通过对脉冲的载波包络相位(CEP)稳定，垂直于光传播方向(横向)的附加对称性破缺已经成为可能。这个项目的主要目标是演示CEP稳定的定制强光场与手性分子相互作用中的侧向对称性破缺。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，我们将使用具有定制偏振态和宽激发波长范围的CEP稳定的超短脉冲作为先进的光源，用于电离和通过速度图成像重建三维光电子角分布以进行探测。通过将CEP稳定与脉冲剪裁技术相结合，将获得对手性分子多光子电离中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.