Phase locked bichromatic polarization tailored femtosecond laser fields to study and control electron dynamics in chiral molecules.

锁相双色偏振定制飞秒激光场，用于研究和控制手性分子中的电子动力学。

• 批准号: 281051436
• 负责人: Professor Dr. Thomas Baumert
• 金额: --
• 依托单位: Institut für Physik
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/281051436?language=en
• 关键词: Phase; locked; bichromatic; polarization; tailored

Photoelectron Circular Dichroism (PECD) is a CD effect based on an electric dipole transition being large in comparison to ordinary CD effects. Recently we have measured a PECD up to the ten percent regime in a 2+1 resonance enhanced multi photon ionization (REMPI) scheme with femtosecond laser pulses on randomly oriented molecules of Camphor, Fenchone and Norcamphor in the gas phase at an excitation wavelength of 400 nm. We observed contributions from higher order Legendre polynomials up to two times the number of photons absorbed. Different modulations and amplitudes of the contributing Legendre polynomials are observed despite the similarity in chemical structure and absorption spectrum. Our intensity studies revealed dissociative ionization as the origin of the PECD effect and ionization of the intermediate resonance is dominating the signal. So far there is a lack of a consistent theoretical description of the PECD in the multiphoton case and the role of the intermediate is theoretically unclear. Progress is expected as several theoretical groups are currently working on this topic. Here we propose to put PECD measurements to a new level and use phase locked bichromatic (400 nm / 800 nm) polarization tailored femtosecond laser fields to study and control electron dynamics in chiral molecules, where the above mentioned bicyclic ketones serve as prototypes. The experiments are directed to study the influence of the photons angular momentum on resonances and continuum states and to study PECD in unusual polarization fields. A systematic study using bichromatic polarization tailored laser fields on the ionization dynamics in general has not been performed so far. This is partly due to the lack of a proper optical set-up to create these tailored light fields. One of the objectives of this proposal is therefore the implementation and characterization of a phase locked bichromatic bipolarization set-up with independent selectable polarization states and intensities for the two radiation fields as well as allowing for phase stable tuning from the optical interference regime (temporal overlap of the two radiation fields) to the pure quantum interference regime (temporally separated pulses) and a pump-probe regime with attenuated pulses. Besides a test of the set-up on achiral potassium atoms, we will for the first time apply such fields to ionize randomly oriented chiral molecules. The three dimensional momentum distribution can be inferred from tomographic reconstruction techniques developed recently in our laboratories. Amongst a whole variety of different physical topics, we expect promising results from two specific approaches: We will investigate to what extent the PECD effect can be increased using laser prepared nonisotropic distributions. We will study PECD in unusual polarization fields like for example 'cloverleaf' or 'butterfly' shapes, where the latter might open a route to create a PECD effect within one polarization field.

光电子圆二色性（PECD）是一种基于电偶极跃迁的CD效应，与普通CD效应相比，电偶极跃迁较大。最近，我们已经测量了PECD高达百分之十的制度，在2+1共振增强多光子电离（REMPI）计划与飞秒激光脉冲随机取向的樟脑，茴香酮和降樟脑在气相中的分子在400 nm的激发波长。我们观察到的贡献，从高阶勒让德多项式吸收的光子数的两倍。不同的调制和幅度的贡献勒让德多项式的观察，尽管在化学结构和吸收光谱的相似性。我们的强度研究表明，解离电离的PECD效应的起源和电离的中间共振是占主导地位的信号。到目前为止，在多光子情况下，PECD缺乏一致的理论描述，中间体的作用在理论上也不清楚。预计将取得进展，因为目前有几个理论小组正在研究这一专题。在这里，我们建议把PECD测量到一个新的水平，并使用锁相双色（400 nm / 800 nm）偏振定制飞秒激光场来研究和控制手性分子中的电子动力学，其中上述双环酮作为原型。实验的目的是研究光子角动量对共振态和连续态的影响，以及在非寻常偏振场中的光子等效等效电路。利用双色偏振剪裁激光场对电离动力学的系统研究，目前还没有进行。这部分是由于缺乏适当的光学设置来创建这些定制的光场。因此，本建议的目的之一是实现和表征具有两个辐射场的独立可选偏振态和强度的锁相双色双偏振设置，以及允许从光学干涉机制进行相位稳定调谐（两个辐射场的时间重叠）到纯量子干涉区（时间上分离的脉冲）和具有衰减脉冲的泵浦-探测机制。除了对非手性钾原子的设置进行测试外，我们将首次将这种场应用于非随机取向的手性分子。三维动量分布可以从我们实验室最近发展的层析重建技术中推断出来。在各种不同的物理主题中，我们期望从两种具体方法中获得有希望的结果：我们将研究使用激光制备的各向异性分布可以在多大程度上增加PECD效应。我们将研究PECD在不寻常的偏振领域，如“三叶草”或“蝴蝶”的形状，后者可能会打开一条路线，创造一个偏振领域内的PECD效应。