Femtosecond Dynamics - Koch Group

Koch group photo taken outside TU Graz' new campus

We investigate how light interacts with matter. In particular we are interested in ultrafast processes such as nuclear and electronic dynamics, or the transfer of energy and charges, which we study in real time with femtosecond laser pulses. A repertoire of experimental approaches allows us to observe these primary processes in various different systems under diverse environmental conditions: Form isolated molecules in gas phase, over molecular clusters inside superfluid helium nanodroplets, to nanostructured solids.

Master's Thesis: Implementing White Light Probe in Femtosecond Transient Absorption Microscope

Our group is looking for a highly motivated Master student who is interested in extending our transient absorption microscope (TAM) setup to wavelength-resolved detection using white light generation, a highly nonlinear process in crystals. Together with PhD student Robert Schwarzl, the student will implement a high-speed grating spectrometer and a white light generation beam path.

TAM is a state-of-the-art spectroscopy technique, providing femtosecond temporal and (sub-)micrometer spatial resolution. It allows tracking the flow of energy and charges in real time in novel materials like quantum dots, plasmonic structures, or organic thin films. Using femtosecond lasers, the method is able to observe processes at least three orders of magnitude faster than the best electrical components. The extension towards white-light probe will allow us to perform a full-range material characterization in a matter of minutes instead of weeks.

Master's Thesis: Characterization of Higher Excitons in Squaraines using Femtosecond Transient Absorption Microscopy

2D TA image, delay scan, Jablonski diagram

Our group is looking for a highly motivated Master student who is interested in investigating a class of organic semiconductors called Squaraines. Together with PhD student Robert Schwarzl, the student will perform time-, space- and polarization-resolved measurements of the molecular crystals using femtosecond laser pulses. Results will be discussed with collaborators in Graz, Linz and Philadelphia.

Due to extraordinarily strong intermolecular coupling, squaraines have a fascinating structure-function relationship leading to changes in their exciton absorption spectra known as \emph{Davydov splitting}. Collective, higher molecular excitations which elude more traditional spectroscopic methods will be investigated using the ultrafast technique Femtosecond Transient Absorption Microscopy (TAM). The method allows us to achieve (sub-)micrometer spatial resolution and femtosecond temporal resolution, two crucial aspects for the highly anisotropic materials with picosecond excitation lifetimes.

Latest News

2024-03: FWF Squaraine project starts. Squaraines are a highly versatile class of organic chromophores and semiconductors and show exceptionally strong intermolecular coupling, resulting in pronounced changes to the optical absorption. We investigate dynamics and higher excitations of these extremely interesting molecular aggregates.

2021-07-09: Nature Communications paper. First demonstration that electrons in liquids can be accelerated with laser pulses. Nat Commun 12, 4204

2020-12-10: Bernhard Thaler receives the Award of Excellence from the Austrian Ministry of Education, Science and Research for his PhD Thesis on ultrafast dnamics in He droplets – congratulations Bernhard!

2020-05-01: New Project starts. Femtosecond photochemistry in a quantum solvent, funded by the FWF (P33166), sets out to explore the opportunities and limits of femtosecond specroscopy inside He droplets. - See, He drops can pick up money.

2020-03-20: PRL paper
Long-Lived Nuclear Coherences inside Helium Nanodroplets: Our observation of a  nuclear wave packet motion of molecules inside superfluid He nanodroplets is a big step towards ultrafast photochemistry inside these nano-cryo-containers. We discover that the quantum fluid is a great solvent with extremely low influence on the molecule.
Phys Rev Lett 124, 115301 (2020) | full text
Focus stories: APS Physics magazine | AIP Inside Science
Press coverage: | ChemEurope| Chemie.DE | APA | Der Standard | TU Graz

2020-01-10: JPCL paper
Progress in the understanding of energy transfer in a molecule: Through a collaboration with the González group we obtain detailled insight into the population transfer in acetone.
J. Phys. Chem. Lett. 11, 1443  (2020)
press coverage: ChemEuropeChemie.DE | EurekAlert! | ScienceDaily| PhysOrg | Der Standard | Die Presse

All images © TU Graz/Institute of Experimental Physics