Imaging of attosecond electron dynamics in atoms, molecules and nanostructures

Prof. M. Kling, Experimental Physics, MPQ

Main research areas: Imaging of attosecond - femtosecond electron and nuclear dynamics in molecules and nanostructures; real-time observation and control of collective electron motions (plasmons) in nanostructures.

Processes that lead to chemical/biological transformations consist of elementary physical steps that occur on the femtosecond (1 fs = 10^-15 s), or in some cases, the sub-femtosecond (attosecond, 1 as = 10^-18s) timescale. The natural time-scale for the making and breaking of chemical bonds is the vibrational period. These timescales are typically in the femtosecond domain. Electrons are responsible for the creation of the potential energy landscapes that drive the atomic motion and adapt on even faster timescales. The typical timescale for electronic motion is the atomic unit of time (1 a.u. = 0.024 fs = 24 as). In the past, direct measurements on these timescales have not been possible.

After their first realization in 2001, the generation and characterization of attosecond laser pulses has been significantly advanced. Two major tools are now at hand that can be used to explore ultrafast physics. The first is the ability to control electronic motion via waveform-controlled laser fields. The second is the availability of single attosecond pulses that can be used to probe electronic motion in real-time. The attosecond imaging group aims to apply these tools in investigations on the electron dynamics in complex materials, where the light-induced dynamics is not only governed by the response of single electrons but the correlated and collective dynamics of many electrons.

Nanostructured materials, nanoparticles and clusters are ideally suited to study collective electronic phenomena. These materials bridge the gap between atoms and molecules and the bulk materials. The motivation for studies on these materials is related to the possibility of tailoring their dynamical behavior on the basis of size and shape. Nanomaterials have wide applications ranging from markers in medicine and biology to quantum computers. In a number of the important physical phenomena that are related to these applications, the excitation and relaxation of electrons play a key role. Collective electron excitations (plasmons) are typical signatures in the optical response of nanoparticles and the possibility to control these excitations by means of the size and shape of the nanoparticle is one of the foundations of nanoscience. The localization length of surface plasmon eigenmodes in nanoplasmonics is determined by the size of the constituent nanoparticles and can be on order of several nanometers. The relaxation rate of the surface plasmon polarization is across the plasmonic spectrum in the femtosecond range. The fastest dynamics, however, unfolds on much shorter, namely attosecond time scales defined by the inverse spectral bandwidth of the plasmonic resonant region. In our group, we want to directly explore the dynamics of local plasmonic fields in nanoparticles, nanostructured materials and clusters with attosecond time resolution. The combination of ultrahigh temporal and spatial resolution might provide essential information for the design of novel ultrafast optoelectronic and next-generation nanoplasmonic devices.