Coherent two-dimensional spectroscopy in the gas phase
The goal of this project is to study isolated nanosystems with coherent two-dimensional (2D) spectroscopy in order to gain a better understanding of microscopic processes taking place on the atomic and molecular level. 2D spectroscopy (Fig 1a) is a unique experimental technique, which provides both, high time and frequency resolution. As no other technique, it is capable of directly revealing couplings and energy transfer mechanisms in 2D frequency-correlation maps (Fig. 1b), which makes it the ideal method to investigate molecular dynamics on ultrafast (femtosecond) time scales.
While, so far, 2D spectroscopy has been mainly applied to condensed phase systems, we have developed a highly sensitive experimental setup to apply the method to dilute gas phase samples, ranging from molecular beams, doped clusters and even to ultracold atoms captured in magneto-optical traps [1-3].
One research focus of this project lies on the investigation of molecular nanosystems, that are single molecules up to small molecular complexes solvated in rare-gas clusters. These model systems are ideal to study the properties and dynamics of individual molecular units relevant in nature, for instance in photosynthesis, photovoltaics and photocatalysis. The goal is to gain a better understanding of the fundamental intra- and inter-molecular mechanisms as well as the role of the local environment on the molecular dynamics. The unique combination of the well-controlled systems with 2D spectroscopy and selective detection schemes, available in the gas phase, enable us to deduce a precise and comprehensive picture of the ultrafast photodynamics taking place in the probed systems. The second research focus of the project lies on the investigation of atomic many-body systems and their interaction mechanism under extremely dilute conditions. To this end, we have developed a highly sensitive detection scheme for weak dipolar interactions in atomic gases [4,5]. The method is based on nonlinear time-domain interferometry and allows us to extract interaction signatures despite strong inhomogeneous broadening in the disordered atomic ensembles. This research project is relevant for our understanding of fundamental inter-particle interactions under extreme conditions but also in view of implications for quantum optics.
Figure 1: a) Experimental scheme to record two-dimensional frequency-correlations maps of a doped cluster/droplet beam. b) Comparison of 2D and 1D spectrum. Off-diagonal features, clearly separated in 2D spectra, are difficult to identify in 1D spectra. These off-diagonal signals provide information about couplings and energy relaxation pathways.
