Abstract
ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), considered as the most stable heavy metal fluoride glass and the excellent host for rare-earth ions, has been extensively used for efficient and compact ultraviolet, visible, and infrared fiber lasers due to its low intrinsic loss, wide transparency window, and small phonon energy. In this paper, the historical progress and the properties of fluoride glasses and the fabrication of ZBLAN fibers are briefly described. Advances of infrared, upconversion, and supercontinuum ZBLAN fiber lasers are addressed in detail. Finally, constraints on the power scaling of ZBLAN fiber lasers are analyzed and discussed. ZBLAN fiber lasers are showing promise of generating high-power emissions covering from ultraviolet to mid-infrared considering the recent advances in newly designed optical fibers, beam-shaped high-power pump diodes, beam combining techniques, and heat-dissipating technology.
Highlights
Since the first demonstration of laser emission from a ruby crystal in 1960 [1], hundreds of crystals and glasses doped with rare-earth ions have been fabricated and utilized in solid-state lasers to generate coherent emissions at different wavelengths
Since detailed descriptions of heavy metal fluoride (HMF) glasses and complete investigations of their properties can be found in the literature [19,20,21,22,23,24,25,26,27,28], we only briefly discuss here the synthesis of fluoride glasses and the fabrication of ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fibers
Since these CW operations were demonstrated at relatively low power levels, the population bottleneck caused by the shorter lifetime of the upper laser level relative to the lower laser level was not noticed until Bedo [69, 70] reported the saturation of the 2.71 μm laser output from Er3+-doped ZBLAN fibers with different concentrations pumped by a Ti:sapphire laser at 791 nm
Summary
Since the first demonstration of laser emission from a ruby crystal (chromium-doped corundum) in 1960 [1], hundreds of crystals and glasses doped with rare-earth ions have been fabricated and utilized in solid-state lasers to generate coherent emissions at different wavelengths. Silicate, phosphate, fluoride, and chalcogenide glasses can be drawn into single-mode fibers. Fluoride and chalcogenide glasses have drawn much attention because they are found to have low phonon energy and mid-infrared transparency. These glasses are excellent candidates for fiber lasers in visible and mid-infrared regions where emissions are hard to be obtained from silicate and phosphate fibers. In contrast to chalcogenide fiber lasers, a plenty of fluoride glass fiber lasers have been reported in the past two decades and ten-watt-level output powers have already been demonstrated [14,15,16].
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