Regensburg 2007 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 26: INTERNAL SYMPOSIUM Optical Spectroscopy I

CPP 26.5: Invited Talk

Thursday, March 29, 2007, 11:30–12:00, H40

Optimal Control of Femtosecond Time-Resolved Four-Wave Mixing for the Selective Excitation of Molecular Modes — •Arnulf Materny — International University Bremen (Jacobs University Bremen as of spring 2007), Campus Ring 1, 28759 Bremen

A selective excitation of vibrational modes even for complex molecules would be of considerable interest for the control of chemical reactions. Due to the fast intramolecular vibrational energy redistribution (IVR) process, the selectivity can usually not be achieved. The internal energy transport takes place on a time scale of few picoseconds or even less. Therefore, the use of ultrashort laser pulses in the femtosecond range seems to open up a possibility to overcome the IVR problem. However, now at least all modes within the broad frequency spectrum of the pulses are excited. A solution to this problem is the phase and/or amplitude modulation of the pulse spectrum. It will be demonstrated that by an optimization of the pulse shape in a self-learning loop arrangement guided by an evolutionary algorithm the control of mode excitations can be achieved. Using a coherent anti-Stokes Raman scattering interaction the enhancement as well as suppression of molecular vibrations are demonstrated for both electronically resonant and non-resonant stimulating laser pulses.