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MO: Fachverband Molekülphysik

MO 56: Poster: Femtosecond Spectroscopy

MO 56.8: Poster

Donnerstag, 22. März 2007, 16:30–18:30, Poster A

Pump – Degenerate Four Wave Mixing (Pump – DFWM) as a technique for time resolving and controlling molecular excited state dynamics — •Jürgen Hauer, Tiago Buckup, and Marcus Motzkus — Physikalische Chemie, Philipps-Universität Marburg, D-35032 Marburg, Germany

Time resolving structural dynamics on short lived molecular excited states presents a challenging yet wide ranging field of ultrafast spectroscopy. We present a technique which delivers highly resolved vibrational modes as well as information on the concerned electronic states. The potential for coherent control of the observed dynamics is outlined and demonstrated on first results.

The presented method is based upon Degenerate Four Wave Mixing (DFWM). By adding an additional pump pulse preceding the DFWM – sequence (Pump – DFWM), resolving excited state dynamics becomes feasible. By chopping the pump – pulse, the observed vibrational modes can be unambiguously discerned from ground state dynamics. The time resolution achieved is only limited by the duration of the employed ultrashort laser pulses (sub 20 fs in the presented set up). Since Pump - DFWM is a pure time domain method, the spectral resolution is typically only limited by the vibrational life time. Under experimental conditions, resolution better than 20 cm⁻¹ can be achieved.

Coherent control of excited state behaviour is achieved by phase modulating the pump pulse, whereas the DFWM – sequence serves as a heterodyne detection method. The effects of intuitive pulse shapes on the early excited dynamics of β carotene are discussed.