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An ultra-cold target for precision studies of heavy-ion atom collisions

Antragsteller Dr. Daniel Fischer
Fachliche Zuordnung Optik, Quantenoptik und Physik der Atome, Moleküle und Plasmen
Förderung Förderung von 2008 bis 2017
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 76879065
 
Erstellungsjahr 2016

Zusammenfassung der Projektergebnisse

In the course of the Emmi-Noether project “An ultra-cold target for precision studies of heavyion atom collisions” a powerful and novel experimental technique, the MOTReMi was developed. This method represents a significant experimental advancement for the study of atomic fragmentation processes. The MOTReMi is a combination of two state-of-the-art techniques: a ‘reaction microscope’ also referred to as COLTRIMS (cold target recoil ion spectroscopy) and a magneto-optical trap (MOT). In the last two decades COLTRIMS experiments led to several breakthroughs in our understanding of the dynamics of atomic or molecular fragmentation processes induced by the interactions with charged projectiles, synchrotron radiation, intense femto- and attosecond light pulses, as well as free electron lasers. However, one important limitation of COLTRIMS is the target temperature that can be reached (about 1 K) using a supersonic jet and the applicability to only a few types of target gases. In the course of present project, a reaction microscope was for the first time successfully combined with a MOT providing a target with a temperature of about 1 mK. This combination is extremely challenging, and has – so far unsuccessfully – been attempted by some of the world's leading groups in the field. In the present project, the intrinsic incompatibilities were resolved with an elaborate design and an unconventional operation of the involved techniques. The MOTReMi enables observing atomic reaction dynamics and mapping of wave functions of the emitted electrons in unprecedented detail with momentum resolutions of only a few hundredths of an atomic unit. In several respects it represents a significant break-through: On the one hand, with the alkali and alkaline earth metals a large and very important class of atomic species becomes available as targets for kinematically complete scattering experiments. These are particularly appealing, because they have only one (or two, respectively) valence electrons representing rather simple atomic systems which are most suitable to study the most fundamental aspects of atomic dynamics. On the other hand, the MOTReMi technique offers a lot of flexibility for the state preparation and manipulation of atoms by optical lasers. For example, the initial target state can be prepared in an excited state and even be polarized by means of laser fields. This provides unique possibilities to study e.g. the dependence of the fragmentation dynamics on the initial target state or target orientation and fundamental symmetry properties. The inaugural experiments of the MOTReMi were performed at the storage ring TSR installed at the MPIK investigating the ionization dynamics of lithium atoms in collisions with ions. Earlier studies of this very fundamental process with a helium target showed surprising and to date not fully resolved discrepancies to theory that were controversially debated and partially assigned to complex resolution effects. Already in the first MOTReMi experiments, a tremendous resolution has been achieved, which was by a factor of about 3 to 5 better than the earlier experiments on helium. Moreover, by means of optical excitation studying initial-state and angular-momentum orientation dependences of the cross sections in fast ion-atom collisions became possible for the first time. The outstanding quality as well as the diversity of the gathered data provides a substantially more detailed view into the collision dynamics than it was possible before. The new technique represents the first step in applying the comprehensive toolbox developed for the preparation and manipulation of atomic quantum-gases to scattering experiments. In future experiments, optical trapping, cooling (even to degeneracy) and manipulation will allow for an unprecedented level of target control providing insights into the correlated dynamics of few-particle quantum-systems on a hitherto unreachable level of detail.

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