Probing Correlated Ionization Dynamics

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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.