Dynamic Spectroscopies

Prof. J. Hauer, TUM

The Dynamic Spectroscopy group is a team of experimental physicists and physical chemists. We measure, analyze and simulate time-resolved optical signals of molecules and molecular complexes. Our experimental toolbox contains techniques such as pump-probe, heterodyned and homodyned transient grating, and as the most comprehensive method two-dimensional electronic spectroscopy, both in single- and double-quantum variants.

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Pump-Probe

Pump-probe or transient absorption spectroscopy is the by far most wide spread of ultrafast techniques. The transmission of a probe pulse through the investigated sample is recorded with and without the presence of a preceding pump-pulse. By scanning the delay of the probe with respect to the pump, transient molecular species such electronic excited states or vibrational modes can be monitored in their time behaviour. We use pump-probe as a first view on molecular dynamics and to determine lifetimes of electronically excited states. It is also a reference technique for our central method, two-dimensional electronic spectroscopy.

Two-dimensional electronic spectroscopy

Two-dimensional electronic spectroscopy (2D-ES) and pump-probe are directly related techniques with many similarities. From a theoretical point of view, 2D-ES and pump-probe share the same non-linear signal, but differ in its representation: in pump-probe one integrates over all excitation frequencies and plots the resulting signal in its time dependence. In 2D-ES on the other hand, the signal gets resolved in excitation frequency. What used to be a simple transient in pump-probe, becomes a time-dependent energy landscape in 2D-ES. The coordinates of these landscapes are excitation and emission frequencies. This increase in dimensionality leads to a much richer data basis for model building. Specifically, 2D-ES highlights energy transfer and coherence pathways which could remain elusive in excitation frequency-integrated techniques such as pump-probe.