Material metrics for laser cooling of solids

Jedo Kim, Ankur Kapoor, and Massoud Kaviany
Phys. Rev. B 77, 115127 – Published 19 March 2008

Abstract

The material metrics for optimal laser cooling of ion-doped solids are derived using atomic and molecular dynamics properties of the constituents. The anti-Stokes process is modeled as an optical phonon coupling of the bound electron, followed by a photon absorption. The transition dipole moment is estimated using a simplified charge-displacement model and the Judd–Ofelt theory of rare-earth ions both suggesting that transitions with high-energy gaps and similar angular momentum states should be used. The electron-phonon coupling is interpreted as a derivative of electronic energy with respect to displacement of the nearest neighboring ligands whose stretching mode frequency is approximated using the molecular data. The Debye-Gaussian model is used for the phonon density of states of diatomic crystal. Then, the Fermi golden rule is used for photon-induced, phonon-assisted electronic transition probability and applied to the cooling rate equation by defining a phonon-assisted transition dipole moment. Based on the material metrics, an example blend is investigated for its cooling performance and a general guide is proposed for selection of better performing laser cooling hosts. Furthermore, the cooling rate limits are discussed and three distinct characteristic times are identified with the photon-induced, phonon-assisted transition time controlling the rate. The metrics guide the selection of host materials for optimal cooling, and predict a noticeable increase in the absorption rate when using a blend of cation atoms.

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  • Received 4 December 2007

DOI:https://doi.org/10.1103/PhysRevB.77.115127

©2008 American Physical Society

Authors & Affiliations

Jedo Kim, Ankur Kapoor, and Massoud Kaviany*

  • Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2125, USA

  • *kaviany@umich.edu

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Issue

Vol. 77, Iss. 11 — 15 March 2008

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