Berlin 2005 – wissenschaftliches Programm
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MO: Molekülphysik
MO 23: Femtosecond Spectroscopy
MO 23.7: Vortrag
Samstag, 5. März 2005, 15:30–15:45, HU 2091
A New Spectroscopic Method: Frequency-Selective Spectroscopy using Shaped Femtosecond Laser Pulses — •Jakow Konradi, Ajay K. Singh, and Arnulf Materny — International University Bremen, School of Engineering and Science, Campus Ring 1, 28759 Bremen (e-mail: a.materny@iu-bremen.de)
The use of femtosecond lasers limits the spectral resolution considerably. Fourier-transform limited pulses of a length of 100 fs have a spectral width of approximately 150 cm−1. Therefore, ultrashort pulses are exclusively used for spectroscopy in the time domain. Recently, we have demonstrated that a change of the chirp of femtosecond laser pulses has a striking influence on the spectrum arising from the light-matter interaction. In our contribution we will present our latest results on frequency-selective spectroscopy with spectrally broad ultrashort pulses. Using nonlinear four-wave mixing spectroscopic techniques like CARS (coherent anti-Stokes Raman scattering), we excite several vibrational modes in a molecule at the same time. These modes usually contribute to the spectrum resulting in a poorly resolved counterpart of the spectrum obtained using narrow band lasers. This changes completely if the phase shape of the laser pulse is varied. Applying a computer-controlled pulse shaper we are able to optimize the specific spectral lines. For the optimization we use as feedback the spectrum detected by a polychromator in a learning evolutionary algorithm that step by step improves the phase of one of the exciting femtosecond laser pulses. With this method we are able to filter out week lines and/or suppress lines that normally dominate the spectrum due to their large intensity.