Attosecond pulses created by high harmonic generation (HHG) in gases allow us to study fundamental light-matter interaction processes with novel experimental techniques. The ultrashort light pulse leads to the creation of a wave packet that can be exploited to investigate attosecond dynamics in ionized systems. We apply interferometric techniques to access the correlated multi-electron dynamics in complex systems aiming to monitor in real time charge migration/transfer.
Collaborators at LU: Anne L'Huillier and Cord Arnold
Imaging dynamics of small molecules
Atoms and molecules in electronically excited states decay via various processes which lead to bond breaking and ion formation, producing neutral and charged constituents that react with their neighbors. These processes occur everywhere, from car engines to industrial chemical plants. Ionization processes occur naturally in the Earth's upper atmosphere and at the Earth's surface and are largely responsible for radiation damage in biological molecules. Generally high-energy photoionization or collisional ionization leads to a greater the number of possible reaction pathways for higher energy transfer resulting in greater “damage” to the system.
On a fundamental level we are able to image the molecule by careful measurement of the ion trajectories. This provides a tool for connecting molecular geometry in fragmentation to kinematics and to the time scale of competing processes. This is a major field of research and momentum spectroscopy can help to answer fundamental questions which play an important role in many branches of physics, chemistry and biology.
Cluster dynamics - a step towards complexity
Photoinduced processes in complex systems can be modeled as a sequence of events initiated by the absorption of a photon. Photoionization of an atomic electron is followed by electronic relaxation which results in a migration of charge within the atom. The need to understand how this initial event leads to higher ionization states and dynamic effects in complex systems such as biomolecules or nanostructured materials is motivated by biological processes and by possible light-harvesting applications. The extreme complexity in understanding the series of sequential events lies in the interplay between electrons and ions especially when the times scales are similar. This phenomenon, called the break down of the “Born-Oppenheimer” approximation, is surprisingly common for large molecules and its investigation is one of the great challenges of this century.
Weakly bound, atomic and molecular, clusters have been the subject of many studies to investigate structures, dynamics and energetics of nano-scale objects, with the goal to understand the evolution of their properties from isolated atoms to the bulk solid. The ability to tailor them in large variety of ways, for example size, geometry, chemical environment..., make these clusters ideal as model systems to understand how the primary sequence of processes is affected by surrounding atoms or molecules.
Collaborators at LU: Maxim Tchaplyguine and Noelle Walsh
Instrumentation: Imaging spectroscopies
Instrumentation for carrying out multicoincidence expeirments between ionized fragments and photoelectrons is developed within the group. Design and characterization studies have been carried out for a high-resolution three-dimensional ion imaging system for use with synchrotron radiation, and a full three-dimensional imaging system has been designed and constructed for pulsed XUV laser systems.
Collaborators at LU: Per Johnsson