T3.3 Towards Laser Cooling in Rare Earth Doped Silicate Glass Fibers

Peter D. Dragic (University of Illinois at Urbana-Champaign)


Laser cooling in solids can be achieved by pumping a rare earth (RE) element at an energy less than its average spontaneous emission energy. Phonons then can be extracted from the host material; under proper conditions giving rise to temperatures reaching even the cryogenic range. Since laser cooling efficiency usually is only on the order of a few percent, the material system must be free of parasitic heating processes, such as non-radiative decay, impurity absorption, etc. This places particularly strict requirements on the quality of the optical host material and the local environment of the RE. Owing in part to its simple two-level f-f transition diagram, possessing only one excited state (and therefore lacking upconversion or excited state absorption processes), and a relatively high concentration quenching limit, Yb3+ is a preferred RE ion for the cooling application. While laser cooling has been demonstrated in several Yb-doped crystalline materials, laser cooling of Yb-doped glass has been most successful in fluorides, namely ZBLAN, whereas the observation of cooling in silicate hosts has remained elusive. Due to its being physically robust, and having a relatively high optical damage threshold, doped silica is the material of choice for high power, multi-kW fiber lasers in the near infrared. Demonstration of fluorescence cooling in these materials could therefore enable, for example, lasers that generate no internal heat. The correlated efforts to tailor the host to achieve cooling in silicate glass fibers will be presented. Both conventional (including nanoparticle doped) and unconventional optical fiber fabrication methods, as well as procedures to measure and quantify glass properties and cooling, will be discussed. 

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SYMPOSIUM T3 – OPTICAL DEVICE AND PHENOMENON
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Peter D. Dragic
Location: Technological Institute M128