Femtosecond Spectroscopy Research Group „InFemto”
Team leader: prof. dr hab. Wojciech Gadomski
Team leader’s e-mail address: gado@chem.uw.edu.pl
Brief description of the research topic:
The research focus of the group includes both experimental studies using advanced time-resolved femtosecond spectroscopy techniques and classical steady-state spectroscopy, as well as theoretical modeling of studied processes and the development of scientific software. The femtosecond techniques we use include transient absorption (TA), time-resolved terahertz spectroscopy (TRTS), optical Kerr effect (OKE), spatially masked optical Kerr effect (SM-OKE) and transient transmission (TT). We are also involved in construction and programming of femtosecond experimental setups.
Using the TA technique, we observe the photodynamics of optically excited electronic states on timescales ranging from femtoseconds to single nanoseconds, in the near-infrared and visible light ranges. This allows us to study photoinduced chemical reactions and the photodynamics of systems such as dyes, semiconductor systems, and nanoparticles, which have potential applications in photovoltaics, photocatalysis, photodynamic therapy, and photonic materials. We use TRTS method to study the photodynamics of charge carriers, enabling us to observe processes such as carrier trapping and recombination, investigate charge conductivity, and examine light-induced changes in carrier mobility. This technique, when combined with TA measurements, fluorescence, and electrochemical methods, allows for detailed analysis of processes in photoactive materials.
The OKE, SM-OKE and TT techniques allow us to observe ultrafast dynamics (intramolecular vibrations and intermolecular dynamics) in solvents and their mixtures, enabling us to study how intermolecular interactions (van der Waals forces, hydrogen bonding, halogen bonding, etc.) and associated local structures influence the properties of such systems. For simple compounds containing bromine and chlorine, we study nontrivial effects related to intermolecular interactions of isotopologues, which cause changes in the vibrational spectrum that can lead to false estimation of the isotopic composition of a sample. For more complex systems, such as deep eutectic solvents or mixtures containing ionic liquids, combining OKE and TA studies enables us to link the solvent’s structure and dynamics to its effect on solute. This allows us, for example, to investigate how the composition of a solvent/electrolyte affects the photodynamics of photoactive systems. We also use the OKE setup to study phonon dynamics in crystal lattices (i.e. laser induced phase transitions, ultrafast optical switching, etc. ) the rotational dynamics of gas molecules, and the photodynamics of anisotropic metallic nanoparticles.
Experimental work is often conducted in parallel with simulations that help us better understand the dynamics and the associated local structure of the studied systems. Our modeling primarily relies on molecular dynamics simulations, sometimes supported by quantum-mechanical calculations. A significant portion of the data analysis from simulations is performed using software developed within our group, which extensively utilizes graphics processors (GPUs) to accelerate computations.