Metal Ion Sources and Targets for Strong-field Laser Physics

• Applicant: Professor Dr. Gerhard G. Paulus
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 539086056

Strong-field laser physics is still concentrated on neutral gaseous atoms, molecules, and clusters. In fact, the rare gases are the dominating targets in the case of atoms, while the focus has shifted from diatomics towards hydrocarbons and small organic compounds for molecules. In other words, the largest part of the periodic table has not been explored in strong-field laser physics to date. Here we propose to develop a liquid metal ion source (LMIS) in order to use it for basic research in strong-field laser physics. We describe new opportunities accessible by ``new'' targets, in particular atomic and molecular metal ions, including heavy metal ions. In fact, an LMIS can provide a multitude of elements and compounds derived from almost half the periodic table. Concurrently, there are profound technical advantages such as the extremely small source size, which leads to a very small emittance. Therefore, an LMIS has the potential to overcome some of the limitations of conventional ion sources, in particular the severely limited target density in the interaction region. The new source will be used for momentum spectroscopy in ion beam experiments. For molecules, coincidence detection will be used. Due to the superior beam quality, we expect a significantly enhanced momentum resolution. In addition, very well-collimated target beams allow to reduce the focal volume effect, because the ion beam can be confined to a fraction of the focal volume, thus reducing averaging events generated by different intensities in different parts of the focus, which in fact is a long-standing experimental curse in strong-field laser physics.In the framework of this project, we will concentrate on silicon and gold ions as well as on gold molecular ions. For silicon, we take advantage of the fact that an AuSi LMIS produces a high Si^2+ current, even higher than the Si^+ current. This provides an intriguing opportunity to seek for effects of electronic correlation in the ground state on the ionization dynamics with unique sensitivity by comparing ionization to Si^3+ and Si^4+ with different initial charge states. The second opportunity offered by the LMIS is gold. Many of the properties for which gold is famous can be attributed to relativistic effects in its electron shell. By comparing the ionization dynamics of gold to the other group-11 elements, silver, and copper, we expect to identify the impact of relativity on strong-field ionization dynamics. Laser waveforms sculpted on the sub-cycle scale will be used to obtain attosecond temporal information on ionization.The third volume of experiments concerns the gold molecular ion Au_2^+. Electronically, it is similar to the well-studied hydrogen molecular ion, but, at the same time, it is very different, not least due to its enormous mass. We expect very rich ionization dynamics to very high charge states, which we intend to watch on the sub-cycle time scale in a similar way as for the gold atom.

• DFG Programme: Research Grants