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Project B.2.2

Fig. B.2.4: 2D-spectrogram of a solar

Two-dimensional coherent electronic spectroscopy in the UV

2D-UV spectroscopy builds on the newly developed ability to shape sub-20 fs UV pulses at a wide range of wavelengths. First 2D-experiments have been performed in collaboration with H. Kauffmann‘s group (Univ. Vienna). We will use phase-locked pulses in a collinear geometry instead of the usual box arrangement for the excitation. For probing we can either use a replica of the pump pulse or a second synchronised pulse at another wavelength of interest. For the widest probe coverage a femtosecond continuum is available.

For the choice of suitable molecular systems we rely on evidence obtained from transient broadband spectroscopy and theoretical predictions. Organometallic complexes are suitable model systems since the metal-to-metal transitions are usually densely spaced and spectrally narrow. The large spectral width of the pump pulses will therefore allow for the generation of electronic wave packets and the observation of their decay and dephasing. When the duration of the UV-pulses is decreased to sub-10 fs in the setup at the BMO – by cross-phase-modulation or achromatic frequency doubling and subsequent compression with the help of a UV-DAZZLER – DNA bases, oligo-nucleotides and general DNA model systems will become amenable.

So far the energy transfer and the charge motion in excited states of these building blocks of life are not understood; however, they are of utmost importance for many current issues in photobiology. The theoretical tool-kit for simulation and analysis of ultrafast nonlinear spectroscopy will be extended towards the description of signals which are induced by multiple and strong light pulses with the goal of developing a collection of efficient and user-friendly codes for the simulation of N-pulse time- and frequency-resolved optical signals for a broad family of material systems. On coherent spectroscopy a long standing collaboration exists with Prof. H. F. Kauffmann (Vienna).

The only electronic 2D-spectrometer with tunable sub-10 fs pulses in the visible is operated in his lab (see Fig. B.2.4) and used to pursue goals closely related to objective B.2b. The exchange of know-how and transport into the UV will greatly facilitate the full implementation of 2D-UV spectroscopy.