Probing Correlated Ionization Dynamics

高电离态是强场与原子、分子相互作用中普遍存在的一种现象。在可见光和红外波段，多电子电离的动力学在很大程度上可以通过顺序电离来理解，即一个接一个地剥离电子，中间的离子核完全松弛。对于线性激光偏振，已经观察到与这一机制有很大偏离，这可以用电离过程中与母离子重新碰撞的光电子来解释。这个项目集中在抑制再碰撞的条件下的相关电离动力学，特别是与椭圆偏振激光脉冲的电离。为了避免多光子电离和隧道电离的混合效应，采用了离子束作为靶。在时间和位置分辨探测器上测量离子在电离过程中的偏转，从而获得所有电荷状态的3D动量谱。椭圆偏振的使用也提供了使用时钟技术的机会，这是一种非常简单的获得光电离定时信息的方法。通过本课题组开发的模型函数和反卷积算法的拟合，可以从动量谱中提取每个电离步骤的精确定量信息。提出了三个子项目：1.在He+实验中，将建立可以比较多重电离的基线。这些数据也可以与从头算的数字数据进行比较。通过这种方式，可以进行绝对校准的强度测量。将研究He、Ne+和Ar+的多重电离，重点是关联动力学的明确判据。第一个是光电子发射方向的统计。此外，离子束可以被中和。然后，通过与离子的电离进行比较，可以确定中性物质可能的关联电离。相关电离动力学可以通过使用几个周期的脉冲来加速，其中许多电子可能在几个周期内电离。因此，每个光学周期内的激光场的演化决定了电离。在AtoClock方案中，这反映在光电子的发射方向上。因此，相敏检测和时钟的团队合作使人们能够获得关于多电子电离动力学时间的详细信息。

Ionization to high charge states is an ubiquitous phenomenon in the interaction of intense fields with atoms and molecules. At visible and infrared wavelength, the dynamics of multi electron ionization can be understood to a large extend by sequential ionization, i.e. by peeling the electrons one after the other with complete relaxation of the ion core in between. Substantial deviations from this mechanism have been observed for linear laser polarization and can be explained by photoelectrons that recollide with the parent ion during ionization.This project concentrates on correlated ionization dynamics under conditions where recollision is suppressed, specifically ionization with elliptically polarized laser pulses. In order to avoid the mixed re- gime of multiphoton and tunneling ionization, an ion beam is used as a target. The deflection of the ions during the ionization is measured on a time- and position-resolving detector such that 3D momentum spectra are obtained for all charge states. The use of elliptical polarization also offers the opportunity to use the attoclock technique, a remarkably simple method to gain timing information on photoioni- zation. Through a fit of a model function and deconvolution algorithm developed in our group, precise quantitative information can be extracted for each ionization step from the momentum spectra.Three sub projects are proposed:1. In experiments with He+, the baseline against which multiple ionization can be compared, will be created. The data can also be compared to ab-initio numerical data. In this way, absolutely calibrated intensity measurements can be performed.2. Multiple ionization of He, Ne+, and Ar+ will be studied with emphasis on unambiguous criteria of correlated dynamics. The first one is the statistics of the emission direction of the photoelectrons. In addition, the ion beam can be neutralized. Then possible correlated ionization of the neutral species can be identified by comparing with the ionization of the ion.3. Correlated ionization dynamics may be accelerated by using few-cycle pulses for which many elec- trons may ionize in a few cycles. Accordingly, the evolution of the laser field within each optical cycle determines the ionization. In the attoclock scheme, this is reflected in the emission direction of the pho- toelectrons. The team play of phase-sensitive detection and attoclock thus enables access to detailed information on the timing of multi-electron ionization dynamics.