Ultrafast Molecular dynamics

This project focuses the control of fundamental single- and two-electron systems using intense, ultra-short laser fields utilizing ionic targets. The use of ions gives access to fundamental systems of laser-matter interaction and allows the observation of fundamental quantum mechanical processes on the femto- and attosecond time scale.

The measurements are carried out using an ion-beam apparatus that produces a beam of atomic or molecular ions, which is exposed to the controlling laser pulses causing fragmentation and/or ionization. The three-dimensional momenta of all nuclear fragments are detected in coincidence, which allows for reconstruction of the interaction dynamics.

Heteronuclear Limit of Strong-Field Ionization: Fragmentation of HeH+ by Intense Ultrashort Laser Pulses

Intensity-dependent KER distribution of HeH+-ionization by 800nm laser pulses
Grafik: FSU Jena / IOQ

In this work the first experimental investigation of the simplest asymmetric molecule, the helium hydride ion(HeH⁺), in strong laser fields was performed. Helium hydride is only stable as an ion and, therefore, an ion beam apparatus is required for its investigation.
This study focused on how the asymmetric structure, and the resulting permanent dipole moment of the HeH⁺, influence the laser-induced fragmentation.
Both experiment and theory for ionization of HeH⁺ and the isotopologue HeD⁺ reveal, that direct vibrational excitation, with almost no electronic excitation as the initial process, dictates the fragmentation process.

PHYSICAL REVIEW LETTERS 121, 073203 (2018)

Coherent Control at Its Most Fundamental: CEP-Dependent Electron Localization in Photodissociation of a H2+ Molecular Ion Beam Target

Visualization of the electronic probability density in the molecular frame
Grafik: FSU Jena / IOQ

We demonstrated coherent control of electron localization and the fragmentation rate in the simplest molecule, with essentially a single optical cycle. Localization of the electron with respect to the two nuclei is controlled via the CEP of the ultrashort laser pulses.
In contrast to previous CEP-dependent experiments with neutral molecules, the dissociation of the molecular ions is not preceded by a photoionization process, which strongly influences the CEP dependence. The phase dependence is determined by a single-shot phase measurement correlated to the detection of the dissociation fragments.
The experimental results show quantitative agreement with ab initio 3D time-dependent Schrödinger equation calculations that include nuclear vibration and rotation.

PHYSICAL REVIEW LETTERS 111, 093002 (2013)

Multiphoton light-induced molecular potentials

Measured momentum distribution for dissociation of H2 in a tailored laser field
Grafik: FSU Jena / IOQ

Using femtosecond laser pulses, one can manipulate the forces acting on the constituents of a molecule. This makes it possible to shape the potential energy landscape on which the nuclei of a molecule move and, thus, control chemical reactions. Key to this control are tailored laser fields, which can be generated by superimposing phase controlled laser pulses of multiple colors. We have demonstrated that this approach gives rise to surprisingly complex dynamics, even in simple molecules. This complexity results in the strongly structured dissociation pattern shown in Figure I.

This project aims at creating new shapes of tailored laser fields in order to explore routes to controlling simple chemical reactions. We utilize a high-repetition rate fiber laser and the coincidence ion beam apparatus. Data is acquired with an ion beam source (see below) with three-dimensional imaging detector.

M. Kübel, et al., Nature Communications 11, 2596 (2020)