Berlin 2001 – scientific programme

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A: Atomphysik

A 4: Clusters I: Metal Clusters (joint session A and MO)

A 4.7: Talk

Monday, April 2, 2001, 17:15–17:30, H1012

Direct time-resolved observation of electron cooling in size selected sodium clusters — •Michael Schätzel, Markus Maier, Jörn Donges, Bernd v.Issendorff, and Hellmut Haberland — Fakultät für Physik, Universität Freiburg, H.Herderstr.3, 79104 Freiburg

Sodium clusters, which are highly excited by photon absorption from fs-laser pulses, exhibit thermal electron emission. Electrons are emitted from the hot electron gas, which is not in thermal equilibrium with the ionic background. The energy transfer from the electrons to the ions leads to a cooling of the electron gas and thus to a decrease of the electron emission rate, which can be used to determine the cooling rate in a pump-probe experiment. Size selected Na_n⁺ clusters have been irradiated by double fs-laser pulses (400 nm, 140 fs, < 10¹⁰ W/cm²), and photoelectron spectra have been measured as a function of the time delay between the pulses. In this way relaxation times have been measured as a function of cluster size. For Na₉₃⁺ for example a value of about 2 ps was obtained. Experiments using much shorter laser pulses to check for deviations from this purely thermal behaviour are underway.