Berlin 2001 – scientific programme
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MO: Molekülphysik
MO 12: Posters Friday: Spectroscopy
MO 12.18: Poster
Friday, April 6, 2001, 12:30–15:00, AT3
High resolution femtosecond CARS: determination of temperature, collisional lineshifts, rotational constants and molecular anharmonicity — •T. Lang1, P. Beaud2, H.-M. Frey3, and M. Motzkus1 — 1Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, D-85748 Garching, Germany — 2Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland — 3University of Berne, Freiestr. 3, CH-3012 Bern, Switzerland
Nonresonant femtosecond CARS (coherent anti-Stokes Raman scattering) with high spectral resolution is applied on di- and polyatomic molecules (H2, N2, CO2, SO2, C2H2, CHCl3, CH3Cl) in a cell, in a molecular beam and in a flame. Two of the three incident beams are temporally overlapped and prepare a macroscopic coherent excitation in the ground state which is probed by the time delayed third beam. The evolution of signals originating from rotational and vibrational transitions are monitored with fs time resolution. On Mixtures H2-Ar we have used the fs-CARS technique to determine new J-dependent lineshift coefficents at pressures up to p=80 bar. In our setup the evolution of the CARS signal with time is a direct manifestation of the anharmonicity of molecular rotation and vibration, which can be measured with high accuracy (Δω/ω<1:105). Furthermore the CARS signal is sensitive to the rotational population distribution, eg. the temperature. fs-CARS expermiments on diffusion flames (combustion of Methane with air) are presented, which allow for ultrafast temperature measurements with an accuracy better than ΔT=10K.