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AG Zinth - Projects
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Femtosecond Stimulated Raman Spectroscopy in the "Blue" (Development of most modern methods in quantum optics for studies of ultra fast processes in chemistry and biology) Vibrational spectroscopy (IR and Raman) "senses" force constants of chemical bonds and masses of atoms on a molecule. A vibrational spectrum therefore holds detailed information on the structure of molecules. By monitoring the changes of vibrational spectra during a chemical process one can gain insight in the structrural re-arrangments involved. Particularly appealing is the combination of vibrational spectroscopy and femtosecond techniques since one cantrace re-arrangments on the "genuine" chemical time scale. IR spectroscopy with femtosecond time resolution has been around for more than a decade. Raman spectroscopy had to await the invention of femtosecond stimulated Raman spectroscopy (FSRS) a couple of years ago before entering the femtosecond realm. In the FSRS technique a femtosecond white light beam and a spectrally narrow laser beam (Raman pump) cross in the sample. Due to stimulated Raman processes the white light becomes spectrally modulated. By analysing the white light spectrum the Raman spectrum of the sample can be retrieved. A third laser pulse (actinic pulse) induces the photochemical process of interest and time dependent spectra can be recorded in pump probe fashion. We have recently developed a FSRS set-up which is particularly suited to study photochemistry. Many molecules undergoing photochemistry absorb in the UV. We thus designed a FSRS set-up with a "blue" Raman pump pulse. This brings along a substantial resonance enhancement of the solute and relative attenuation of the solvent signal. The blue (390 nm) Raman pump pulse is generated via a chirped pulse addition module allowing for intense and spectrally narrow pulses. The set-up which also incorporates a novel 1 kHz detection module is detailed in a recent publication.
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