Ultrafast Electron Cooling in an Expanding Ultracold Plasma

TL;DR

This paper reports the observation of ultrafast electron cooling in an ultracold plasma formed from a Bose-Einstein condensate, demonstrating rapid temperature relaxation from thousands of Kelvin to near zero within nanoseconds.

Contribution

It provides the first experimental measurement of electron cooling rates in an ultracold plasma created from a BEC, bridging ultracold neutral plasma and ionized nanoclusters regimes.

Findings

Electron temperature drops from 5250 K to below 10 K in less than 500 ns.

Electron cooling rate is approximately 400 K/ps.

Direct measurement of electron temperature relaxation dynamics.

Abstract

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 Bose-Einstein condensate (BEC) by a single femtosecond laser pulse. The large density combined with the extremely 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. 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.