Nanoscience explores the spatial region between bulk material and its atomic or molecular constituents. The change of physical properties in this region can be abrupt and display a number of novel properties.  Experimental methods which can both resolve the structure and the temporal dynamics of the nanostructures are inherent to the understanding of this class of systems. We use synchrotron radiation x-ray scattering and spectroscopy methods combined with laser-based ultrafast methods for the dynamic characterization of nanoscale matter, molecules and crystalline materials, in particular for the analysis of nanoscale dynamics, phonon excitation or phase transitions in the condensed phase. Special emphasis is on the exploitation of the „low alpha mode“ at the KIT Synchrotron, which provides pulses as short as 1 picosecond. In the x-ray regime this can be used for pump-probe experiments with femtosecond laser excitation, while in the THz region the coherent emission of the radiation can be sampled by means of electro-optical techniques.

Central questions are:

• Can light pulses manipulate the phase of functional materials; can one use such effects to switch ferroelectrics, for instance? What are the mechanisms down to an atomic level ?
• Can one watch molecules during the course of a chemical reaction ?
• How do metallic nanoparticles, or nanoparticles with bound proteins, react upon irradiation with intense light pulses ? Can one use these reactions to achieve material processing on a nanoscale, can one achieve targeted effects in biologic materials ?

The main topics of research of the group are:

• Laser control of materials via lattice excitation
• Structural dynamics of nanoparticles
• Nanoparticle synthesis
• Novel sources and methods with ultrahigh time resolution

	Pulsed laser ablation (LAL) and fragmentation (LFL)   Pulsed laser ablation (LAL) and fragmentation (LFL) in liquids has received a lot of attention in the past years due to its prospects as a generalized tool for green production of pure nanoparticles in a wide class of materials. Within the cooperation, we study the formation of nanoparticles by a set of structural methods with high time resolution in situ.   Left: typical setup for probing the structure evolution during pulsed laser ablation of a metal target (yellow block in left image) under water. Due to the extreme conditions a cavitation bubble develops, which contains at first most of the ablated material. See highlight article: https://www.ips.kit.edu/2786_6278.php
Thermal and non-thermal transport in nanostructures and thin films   Thermal and non-thermal transport in nanostructures and thin films are important information for understanding functional materials, such as thermoelectrics. Within a collaboration with University Münster (Material Science) we investigate heat conduction in thin films that are tailored for thermal transport by introducing interfaces. Isotope modulation is one such approach that does not alter electronic properties, but only phonon band structure. Thermal behaviour can be accessed on and nanoscale level by using time-resolved scattering methods.     Right: Pump-probe experiment of a time-resolved thermometry probe of a thin gold transducer film on a nanostructured layer structure. The film acts a heat transducer after absorbing pulsed laser light and signals the time-dependent cooling through probing its lattice expansion by picosecond x-ray pulses.  modulation is one such approach that does not alter electronic properties, but only phonon band structure. Thermal behaviour can be accessed on and nanoscale level by using time-resolved scattering methods.   See highlight article: https://www.ips.kit.edu/2786_2863.php
	X-ray dark-field imaging   X-ray dark-field imaging by Shack-Hartmann contrast variation has been developed in order to visualize the dynamics distribution of nanoparticles in pulsed-laser ablation in liquids in a single-shot-type approach. A wide x-ray beam is partitioned into an array of small individual beamlets, such that each probes absorption, differential phase and dark-field contrast by change of intensity, position and width of the beamlets, respectively. While the detector resolution is sacrificed to probe the beamlets, this approach does not require physical moving of parts or scanning. Therefore it applies well to single-shot probing.   The Shack-Hartmann masks are produced in cooperation with the Institute of Microstructure Technology at KIT either by lithography methods (SHARX) or through Ni-formed stamp masters (CARL).   See highlight article: https://www.ips.kit.edu/2786_6162.php

The group provides expertise on ultrafast optical methods and pulsed lasers, serving research on laser-matter interactions, but also diagnostics of the electron pulses in the ring and the development of new accelerator concepts and techniques. Research is funded by KIT and by individual grants of the German Science foundation (DFG). Collaborations are related to the Center for Applied Photonics Konstanz. We acknowledge the support and provision of beam time by IPS, SLS and ESRF.