Frankfurt 2006 – scientific programme

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MO: Molekülphysik

MO 14: Ultrafast IR and Raman Probe and Control

MO 14.5: Talk

Monday, March 13, 2006, 17:30–17:45, H12

Small Bandwidth 400 nm Pulses for Femtosecond Stimulated Raman Spectroscopy — •Hilmar Schachenmayr, Peter Gilch, and Stefan Laimgruber — Department für Physik, Ludwig-Maximilians-Universität, Oettingenstr. 67, D-80538 München, Germany

Femtosecond Stimulated Raman Spectroscopy (FSRS) copes with several drawbacks of conventional time resolved Raman spectroscopy, as there are weak signal levels, strong fluorescence backgrounds, and an instrumental time bandwidth limit. Thereby, FSRS renders Raman techniques competitive with time resolved IR spectroscopy for monitoring fast molecular re-arrangements. In FSRS spectroscopy a femtosecond white light pulse and an intense laser pulse (Raman pump) cross in the sample. The white light spectrum gets modulated and the modulations can be transformed into the Raman spectrum of the sample. In most application a spectrally narrowed TiSa pulse at 800 nm serves as Raman pump. For many photo-active molecules absorbing in the UV a 400 nm Raman pump is advantageous due to substantial resonance enhancements. We here report on a set-up generating 400 nm pulses for FSRS. Two equally but opposedly in sign chirped 800 nm pulses are mixed in a non-linear crystal. This results in intense small bandwidth 400 nm pulses. With these pulses FSRS spectra with high signal levels and good spectral resolution can be obtained. Examples for their application will be given.