We overview recent advances in visible single- and double-clad fluoride fiber lasers pumped by blue GaN laser diodes. The spectroscopic properties of ZBLAN glasses doped with Pr3+, Ho3+ and Dy3+ ions are revised. Power scalable efficient continuous-wave visible fluoride fiber lasers emitting in the green, yellow, red and deep-red spectral ranges are presented. Pumped by a single-emitter 6-W 443-nm GaN laser diode, a continuous-wave red double-clad Pr:ZBLAN fiber laser delivered 1.51 W at 634.5 nm with a slope efficiency of 31.0%, a laser threshold of 0.63 W and a spatially single-mode output (M2 ~1.02). Employing a high-power fiber-coupled laser module, power scalability up to 4.61 W was achieved at the expense of a lower slope efficiency of 22.8% and an increased laser threshold of 1.74 W. Green Ho:ZBLAN (543 nm) and yellow Dy:ZBLAN (575 nm) fiber lasers with high-brightness core pumping at 450 nm are also reported delivering 100 mW-level output with slope efficiencies of 31.2% and 19.6%, respectively, operating on the fundamental mode. A numerical model to predict the visible laser performance is presented and guidelines for further engineering of visible fiber laser sources are given.
Holmium ions (Ho3+) are attractive for generation of green emission according to the 5F4+ 5S2 → 5 I8 transition. We report on the assessment of the potential of Ho3+ -doped fluoride glasses for green fiber lasers exploiting the double-clad fiber geometry. ZBLAN glasses doped with HoF3 (0.1 – 0.9 mol%) were studied. The absorption cross-section for the 5 I8 → 5F1+ 5G6 transition is 1.75×10-20 cm2 at 448.5 nm. Under excitation in the blue, the glasses exhibit intense green luminescence. The stimulated-emission cross-section for the 5F4+ 5S2 → 5 I8 transition is 0.67×10-20 cm2 at 549 nm. With increasing the HoF3 doping level, the luminescence lifetime of the 5F4+ 5S2 states slowly decreases in the range of 291 – 180 μs. The output performance of a diode-pumped green Ho fiber laser was simulated for a fiber geometry with a double D-shaped inner cladding. The variable parameters were the HoF3 doping level, the fiber length, and the output coupling. It is shown that the generation of watt-level green output from such a laser is possible when using relatively short (<1 m) fibers with low doping levels (about 0.5 mol% HoF3), as well as high transmissions of the output coupler (<60%, depending on the passive losses in the fiber).
We present preliminary results relating to laser emission at 3:16 µm from a Dy fiber laser that is diode pumped at 800 nm. To allow strong diode pump absorption and to capture improved quantum efficiencies resulting from cross relaxation, the Dy:ZBLAN fiber was co-doped with Tm ions in a 10 to 1 concentration ratio to Dy. A resonant energy transfer from Tm to Dy provides an inversion on the 6H13/2 to 6H15/2 transition. Maximum output power of 5.5 mW at a slope efficiency of 1.3 % was produced from a highly non-optimal arrangement. System performance is bench marked against well established resonant pumping of the Dy upper state. Measurement of fluorescence lifetimes of both dopants allows for qualitative assessment of the energy transfer efficiency. A potentially detrimental energy transfer mechanism is identified and discussed.
We report on a 3 W Mid-IR supercontinuum extended up to 4.6 μm based on an all-PM thulium doped fiber gainswitched laser seeding an InF3 fiber. This innovative fiber presents a specific design that increases non-linear effects and shows very weak background losses. Thanks to the versatility of our gain-switched laser, all the pulse parameters have been widely optimized to generate a supercontinuum emission with the highest average power and the largest spectrum.
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