Dr. Markus Kowalewski,
The group works on a wide variety of topics involving photo chemistry, coherent control, polaritonic chemistry, ultrafast spectroscopy, and numerical methods related to quantum dynamics.
Polaritonic Chemistry and Light-Matter Materials
Gaining detailed control over chemical reactions has always been a chemists dream. Quantum coherent control has been pursuing this dream by using specially tailored light fields to control chemical reactions on an atomistic level. With the advancement of cavity quantum electrodynamics and its recent application to molecules, using the quantum properties of light to control photo-chemistry has come into reach. Recent,
ground breaking experiments have show that one can utilize the vacuum field of an optical nano-resonator to significantly modify the potential energy landscape and thus its photo-chemistry. The underlying effect is the formation of so called “dressed states”, which are created when the quantized radiation field mode couples to a molecular electronic transition. In the resulting coupled light-matter system the molecular and the photonic degrees of freedom are heavily mixed. While this effect is well understood for atomic samples, it is not yet fully understood for molecules. The introduction of the nuclear degrees of freedom requires new theoretical frameworks. This effect can be used to modify reaction pathways of chemical and photo-chemical reactions. This opens a wide range of possibilities to engineer novel types of light driven catalysts. We are looking at the underlying mechanisms and are working on building a suitable tool chest for numerical simulations. With the new insight and tools we want to propose new photo-chemical applications.
Ultrafast X-Ray Spectroscopy of Conical Intersections
Conical intersections (CoIns) so far have eluded direct experimental observations. The evidence for their existence is based on ultra fast relaxation rates and other indirect signatures. The rapidly varying energy gap in the vicinity of a C oIn poses a main obstacle for their direct detection. The required extreme combination of temporal and spectral resolution is not available in conventional optical femtosecond experiments. Ultra short laser pulses in the extreme ultraviolet and X-ray laser regime, as they are provided by free electron laser and high harmonic generation sources, fulfill the spectral and temporal requirements to resolve the coupled nuclear+electronic dynamics in the vicinity of CoIns. Ultrafast hard X-ray sources make time-resolved diffraction experiments possible, paving the way to capture the nuclear dynamics of molecules in time as well as in space, with the “molecular movie” of a CoIn as the ultimate goal.
We theoretically investigate novel, X-Ray baseed experimental techniques for spectroscopic detection of CoIns with ultra short X-ray pulses. Simulation strategies for non-linear X-ray spectra and diffraction schemes are applied to molecular system of increasing complexity.