Berlin 2001 – scientific programme

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A: Atomphysik

A 1: Posters Monday (Cluster, Atoms in Fields)

A 1.9: Poster

Monday, April 2, 2001, 12:30–15:00, AT3

Interaction of Magnesium Clusters in Superfluid Helium Droplets with Femtosecond Laser Pulses — •T. Döppner, Th. Diederich, J. Tiggesbäumker, and K.H. Meiwes–Broer — Universität Rostock, FB Physik, Universitätsplatz 3, 18051 Rostock

Magnesium clusters are formed by pick–up of atoms into superfluid helium droplets. In this way ultracold metallic clusters with up to 80 atoms can be produced. After the interaction with intense femtosecond laser fields the fragments are analyzed by high resolution time–of–flight mass spectrometry. For intensities I ≥ 10¹⁵ W/cm² the metal core will be destroyed completely. Only singly and doubly charged magnesium ions with up to 150 helium atoms attached are detected. Their abundance indicates that the helium atoms form shells around the magnesium ions. Pump–probe measurements reveal an interesting abundance dynamics of the MgHe_N⁺ complexes up to 60 ps. The maximum signal enhancement is obtained for a delay time of 4 ps. This is qualitatively similar to previous experiments on the Coulomb explosion of bare metal clusters where a plasmon enhanced ionization was observed with a delay of 0.8 ps [1]. The considerably longer delay in this case indicates caging–effects of the helium matrix.

[1] T. Döppner, S. Teuber, M. Schumacher, J. Tiggesbäumker, K.H. Meiwes–Broer, Appl. Phys. B 71(3), 357 (2000)