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MO: Fachverband Molekülphysik

MO 13: Molekülphysik Poster 1

MO 13.18: Poster

Dienstag, 3. März 2009, 16:30–19:00, VMP 8 Foyer

Rotational dephasing and depopulation rates measured via non-adiabatic alignment — •Nina Owschimikow¹, Jochen Maurer¹, Falk Königsmann¹, Burkhard Schmidt², and Nikolaus Schwentner¹ — ¹Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin — ²Institut für Mathematik, Freie Universität Berlin, Arnimallee 6, 14195 Berlin

Under ambient conditions, bimolecular collisions in gases, and therefore decoherence and dissipation, occur on a picosecond time scale. The dynamics of non-adiabatic laser induced alignment in nitrogen covers exactly this time range and is extremely well described by theory, which allows to quantitatively study relaxation processes of both phase and population. In the experiment, the excitation is followed by recurrent transient bursts of molecular alignment reflecting the phase coherence, which are monitored in a homodyne detected optical Kerr effect experiment. Additionally a non-equilibrium population of M quantum numbers is created upon excitation and is reflected in a weak structureless offset in the detected signal, which is nevertheless amplified by the coherent oscillations due to the quadratic detection. By decomposing the theoretically calculated signal into a coherence part and a population part [1] with two different decay rates and fitting to our data, we show that a slower thermalization of population compared to phase relaxation results in a change of revival shape over time, and thus both rates can be extracted directly from an alignment experiment.

[1] S. Ramakrishna and T. Seideman, Phys. Rev. Lett. 95, 113001 (2006)