Laser-induced forced evaporative cooling of molecular anions below 4 Kelvin

• URL: http://arxiv.org/abs/2211.11264v1
• Date: Mon, 21 Nov 2022 08:53:17 GMT
• Title: Laser-induced forced evaporative cooling of molecular anions below 4 Kelvin
• Authors: Jonas Tauch, Saba Zia Hassan, Markus Noetzold, Eric S. Endres, Roland Wester, and Matthias Weidemueller
• Abstract summary: We demonstrate forced evaporative cooling of anions via a laser beam with photon energies far above the photodetachment threshold of the anion. This corresponds to three orders of magnitude increase in the ions' phase space density approaching the near-strong Coulomb coupling regime. This technique can be used to cool, in principle, any anionic species below liquid helium temperature.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: The study of cold and controlled molecular ions is pivotal for fundamental research in modern physics and chemistry. Investigations into cooling molecular anions, in particular, have proven to be of key consequence for the production of cold antihydrogen, the creation, and study of anionic Coulomb crystals as well as in atmospheric research and astrochemistry. The commonly used anion cooling technique via collisions with a buffer gas is limited by the temperature of the used cryogenic cooling medium. Here, we demonstrate forced evaporative cooling of anions via a laser beam with photon energies far above the photodetachment threshold of the anion. We reach runaway evaporative cooling of an anionic OH$^{-}$ ensemble from an initial temperature of 370(12) K down to 2.2(8) K. This corresponds to three orders of magnitude increase in the ions' phase space density approaching the near-strong Coulomb coupling regime. A quantitative analysis of the experimental results, via a full thermodynamic model including the role of intrinsic collisional heating, represents the anion cooling dynamics without any fitting parameters. This technique can be used to cool, in principle, any anionic species below liquid helium temperature, providing a novel tool to push the frontiers of anion cooling to much lower than the state-of-the-art temperature regimes.

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