Berlin 2001 – scientific programme

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AMPD: EPS AMPD

AMPD 5: Sitzung 5

AMPD 5.3: Talk

Wednesday, April 4, 2001, 10:10–10:35, H105

Ion Coulomb–crystals: A target for photon and particle scattering studies — •Michael Drewsen — Institute of Physics and Astronomy, University of Aarhus, Ny Munkegade, Building 520, DK-8000 Aarhus C, Denmark

When trapped ions are cooled below a certain critical temperature (typically about ten milli–Kelvin) they form spatially ordered structures sometimes referred to as ion Coulomb–crystals. Such crystals of various sizes containing single atomic ion species have for more than ten years been investigated in many types of traps, and recently attention has also been paid to studies and applications of multi–species ion Coulomb–crystals [1–3]. So far ion Coulomb–crystals have only been involved in a very few AMO-physics experiments outside the fields of quantum optics and high resolution spectroscopy. However, due to the fact that the ions in a Coulomb–crystal are both translationally cold and can be stored easily for tens of minutes in a well-defined region in space, such crystals may also serve as ideal targets for a wider range of AMO–experiments.

Recenty, we have applied ion Coulomb–crystals of Mg⁺ and Ca⁺ ions in a linear Paul trap as targets for several reactive scattering experiments with thermal molecular gasses [2]. Beside giving information on reaction rate constants, these experiments have shown that the product molecular ions can stay trapped and be sympathetically cooled to a translational temperature below 100 mK, at which they become a part of a multi–species Coulomb–crystal [2]. Such Coulomb–crystals containing translationally cold molecular ions can ultimately , e.g., be used as a target for dissociation and ionization studies on the single molecule level.

In another recent experiment, photo-ionization of Mg [4], we have used Coulomb–crystals as a "detector". By crossing an atomic beam of Mg atoms with a photo-ionizing laser in the center of a linear Paul trap, we could with very high efficiency trap the produced Mg⁺ ions in the trap. By applying laser cooling to these ions, ion Coulomb–crystals were formed, and the number of ions produced could be estimated with high accuracy by measuring the volume of the crystal. This method can be extended to cases where the produced ions cannot be laser cooled if other laser cooled ions are simultaneously trapped.

Besides the above experiments, other possible applications of ion Coulomb–crystals in AMO–physics will be discussed in the talk.

[1] P. Bowe, L. Hornekær, C. Brodersen, M. Drewsen, J. S. Hangst and J. P. Schiffer, Phys. Rev. Lett. 82, 2071 (1999).

[2] K. Mølhave and M. Drewsen, Phys. Rev. A. 62, 011401(R) (2000).

[3] L. Hornekær, N. Kjærgaard, A. M. Thommesen, and M. Drewsen, to appear in Phys. Rev. Lett.

[4] D. N. Madsen, S. Balslev, M. Drewsen, N. Kjærgaard, Z. Videsen, and J. W. Thomsen, J. Phys. B.:Mol. Opt. Phys. 33, 4981 (2000).