"Attoclock-Rabbitt" - Bicircular laser fields as tool for molecular ionization time measurements

该项目旨在利用定制光场作为工具来回答一个看似简单的问题：通过多光子吸收从分子中射出的光电子的发射时间是否取决于其发射方向？举个例子：我们问，在向分子的C侧或O侧发射的情况下，CO的电子射出是否需要更长的时间。预期的时间差以阿秒为单位。量子力学上的时间差被编码为相位差，因此我们的问题转化为确定电子波包的相位作为与分子轴夹角的函数。为了测量这一阶段，我们提出了一种称为“Attoclock-RABBITT”的新方案。在该方案中，我们将电离瞬间的测量（以类似于已建立的RABBITT技术的方式）与COLTRIMS反应显微镜相结合，通过检测分子离子片段来获得分子参考框架。所采用的激光场将由强圆偏振400 nm场和弱圆共旋转800nm修整场混合组成。正如我们在之前的QUTIF资助期间所了解到的那样，这种圆形场组合将两种颜色之间的相对相位映射到实验室框架中的电子发射角。电子ATI谱的边带显示了已知的RABBITT强度振荡作为该角的函数，从这些振荡可以推断出发射时间。在我们建议的方法中，使用COLTRIMS反应显微镜测量发射电子与分子离子片段的重合。从离子碎片的发射方向，我们可以推断出分子的取向。通过这种方法，我们获得了分子框架中的“Attoclock-RABBITT”轨迹，即电离时间。由于这是一个新颖的方案，我们建议首先在氢原子上进行基准测试。然后，我们将使用它来研究以下预测效应：使用Ne2，我们将搜索在Cohen/ fano干涉下电离时间的预测散度。利用H2，我们将为目前可能进行准精确理论处理的唯一分子提供基准数据。在CO实验中，我们将寻找预测的两侧发射时间的不对称性，目的是在时域中可视化形状共振。最后，对于CF4，我们将测试该技术是否可以应用于更复杂的分子。该项目是QUTIF的核心，因为在以前的几个QUTIF项目中已经探索了定制字段的类型。第一个资助期产生了处理这些领域的广泛理论经验。在实验上，还开发了用于该项目的光学工具。如果没有QUTIF的这种丰富经验，现在就不可能瞄准应用定制领域的下一步。

This project aims to exploit tailored light fields as a tool to answer a seemingly simple question: Does the emission time of a photoelectron ejected from a molecule by multiphoton absorption depend on its emission direction? To give an example: we ask whether the ejection of an electron from CO takes longer in case of emission towards the C or towards the O side of the molecule. The expected time differences are in the attosecond regime. Quantum mechanically time-differences are encoded in phase-differences, thus our question translates to determining the phase of the electron wave packet as function of angle to the molecular axis. To measure this phase, we suggest a new scheme termed “Attoclock-RABBITT”. Within this scheme, we combine the measurement of an ionization instant (in a manner similar to the established RABBITT technique) with a COLTRIMS Reaction Microscope, which gives access to the molecular frame of reference by detection the molecular ion fragments.The employed laser field will consist of a strong circularly polarized 400 nm field mixed with a weak circular 800nm co-rotating dressing field. As we have learned in the previous QUTIF funding period, this bicircular field combination maps the relative phase between the two colors to an electron emission angle in the laboratory frame. Sidebands in the electron ATI spectrum show the known RABBITT intensity oscillations as function of that angle and from these oscillations, one can deduce the emission times. In our suggested approach, the emitted electrons are measured in coincidence with ionic fragments of the molecule using a COLTRIMS Reaction Microscope. From the emission direction of the ionic fragments we are able to deduce the molecular orientation. This way we obtain the “Attoclock-RABBITT” traces, i.e. ionization times, in the molecular frame. As this is a novel scheme, we suggest to first benchmarking it on atomic hydrogen. We will then use it to study the following predicted effects: Using Ne2 we will search for the predicted divergence of the ionization time at a Cohen/Fano-interference. Employing H2 we will provide benchmark data on the only molecule for which quasi-exact theoretical treatment is possible today. In experiments on CO we will search for the predicted asymmetries of the emission time to the two sides and, aim to visualize a shape resonance in the time domain. Finally, for CF4 we will test if the technique can be applied to more complex molecules. The project is at the heart of QUTIF as the types of tailored field have been explored in several previous QUTIF projects. The first funding period has led to widespread theoretical experience in handling these fields. Also experimentally, the optical tools for this project have been developed. Without this extensive experience from QUTIF it would not have been possible to now aim for the next step of application of tailored fields.