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Proceedings Paper

Crystal-field effects in fluoride crystals for optical refrigeration
Author(s): Markus P. Hehlen
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Paper Abstract

The total crystal-field splitting of the 2F7/2 ground-state multiplet of Yb3+ critically determines the cooling efficiency of an optical refrigerator. Crystals with a small 2F7/2 splitting maintain a sizeable thermal population of the initial state of the pumped crystal-field transition at low temperatures, leading to a workable laser-cooling efficiency in the application-relevant cryogenic regime below 120 K. A comprehensive review of the crystal-field splitting of (2S+1)L(J) multiplets in rare-earth-doped fluoride crystals is presented. The concept of crystal-field strength is used to predict the splitting of the 2F7/2 ground-state multiplet from other fluoride crystals doped with other rare earth ions. The analysis correctly predicts the typical 350-450 cm-1 total splitting of 2F7/2 in fluorides, but the accuracy of the method is found to be rather limited. LiKYF5, K2YF5, and Cs2KLnF6 are predicted to have large 2F7/2 splittings that are unfavorable for laser cooling. KY3F10, YLiF4, LuLiF4, and GdLiF4 are among the group of crystals expected to have small 2F7/2 splittings and currently appear to be the most promising hosts for laser cooling with Yb3+. LiBiF4:Yb3+ may have a <350 cm-1 2F7/2 splitting and warrants further study.

Paper Details

Date Published: 18 February 2010
PDF: 12 pages
Proc. SPIE 7614, Laser Refrigeration of Solids III, 761404 (18 February 2010); doi: 10.1117/12.845626
Show Author Affiliations
Markus P. Hehlen, Los Alamos National Lab. (United States)

Published in SPIE Proceedings Vol. 7614:
Laser Refrigeration of Solids III
Richard I. Epstein; Mansoor Sheik-Bahae, Editor(s)

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