Ultrafast Electron Cooling in an Expanding Ultracold Plasma

26 January 2021

Photo: UHH/Großmann

Plasma dynamics critically depends on density and temperature, thus well-controlled experimental realizations are essential benchmarks for theoretical models. The formation of an ultracold plasma can be triggered by ionizing a tunable number of atoms in a micrometer-sized volume of a ⁸⁷Rb Bose-Einstein condensate (BEC) by a single femtosecond laser pulse. The large density combined with the low temperature of the BEC give rise to an initially strongly coupled plasma in a so far unexplored regime bridging ultracold neutral plasma and ionized nanoclusters. Here, we report on ultrafast cooling of electrons, trapped on orbital trajectories in the long-range Coulomb potential of the dense ionic core, with a cooling rate of 400 K ps⁻¹. Furthermore, our experimental setup grants direct access to the electron temperature that relaxes from 5250 K to below 10 K in less than 500 ns.

T. Kroker, M. Großmann, K. Sengstock, M. Drescher, Ph. Wessels-Staarmann*, and J. Simonet*, Nat. Commun. 12, 596 (2021).
* Equal contribution.

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