Düsseldorf 2007 – scientific programme

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SYCP: Symposium Strongly coupled plasmas

SYCP 1: Symposium Strongly Coupled Plasmas

SYCP 1.8: Invited Talk

Tuesday, March 20, 2007, 18:00–18:30, 5D

Initiation of ultracold plasma formation by long-range forces between Rydberg atoms — •Thomas Amthor, Markus Reetz-Lamour, Janne Denskat, and Matthias Weidemüller — Physikalisches Institut, Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg

It has been observed that a gas of ultracold Rydberg atoms spontaneously transforms into a plasma [1]. This plasma is created by an ionization avalanche due to electrons trapped in the potential well formed by the ions. The initial processes releasing the first electrons and thus triggering the ionization have long remained obscure. Collisions with hot background atoms and ionization by black-body radiation were possible candidates, but could not explain all observations. Recent experiments showed that collisions induced by long-range forces between the cold Rydberg atoms represent the main contribution to the inital ionization. The acceleration and subsequent Penning ionization of Rydberg atoms has been investigated under different conditions, the underlying interactions being either of dipole-dipole [2] or van der Waals type [3]. An overview over the effects of mechanical forces with respect to ionization and formation of ultracold plasmas is given. Experimental techniques to follow this process in real time and calculations based on a Monte Carlo model are presented. Scenarios for control and suppression of ionization in Rydberg gases are also discussed.

[1] M. P. Robinson et al., Phys. Rev. Lett. 85, 4466 (2000)

[2] W. Li et al., Phys. Rev. Lett. 94, 173001 (2005)

[3] T. Amthor et al., Phys. Rev. Lett. in press