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Article Dans Une Revue Optics Letters Année : 2016

50.4% slope efficiency thulium-doped large-mode-area fiber laser fabricated by powder technology

Résumé

We report on a triple clad large-mode-area Tm-doped fiber laser with 18 μm core diameter manufactured for the first time by an alternative manufacturing process named REPUSIL. This reactive powder sinter material enables similar properties compared to conventional CVD-made fiber lasers, while offering the potential of producing larger and more uniform material. The fiber characterization in a laser configuration provides a slope efficiency of 47.7% at 20°C, and 50.4% at 0°C with 8 W output power, with a laser peak emission at 1970 nm. Finally, a beam quality near the diffraction-limit (M 2 x;y < 1.1) is proved. Ytterbium-doped fiber lasers have transformed the world of laser sources in recent years [1], in particular, due to impressive works done to circumvent intrinsic limitations imposed by the fiber architecture itself. Recently, new challenges are turned toward the power scaling of fiber lasers based on thulium-doped fibers. The latter enable the generation of radiations in the 1.8– 2.1 μm [2,3] spectral region, which is of great interest for several application fields such as medicine (cornea [4] and prostate [5] surgery), and civil and defense security (remote sensing, LIDAR [6]). Most of the works done in the 2 μm region have been achieved with step-index thulium-doped fibers, the core size being theoretically limited to 30 μm to avoid a significant degradation of the beam quality. The kW-level in average powers in CW regime has then been reached in 2009 [7]. To delve further into the power scaling of such fiber lasers, first demonstrations of thulium-doped large-mode-area (LMA) photonic crystal fibers have been recently reported allowing, for instance, the ability to reach up to 200 mW in peak power in a pulsed regime [8]. Unfortunately, one of the main technological barriers faced for the fabrication of thulium-doped fibers remains obtaining high quantum efficiency. Indeed, thulium-doped fiber lasers are typically pumped at 790 nm where high-power laser diodes are commercially available. Therefore, the large quantum defect between the pump wavelength and the signal wavelength is larger than that obtained in the case of the ytterbium-doped fiber lasers. The Stokes limit in this case is of about 40%, meaning that a large amount of the absorbed power is released as heat, compromising even more the expected power scaling by the appearance of modal instabilities as has already been well described for ytterbium-doped fiber lasers. Nevertheless, the well-known cross-relaxation mechanism that can be observed in thulium-doped gain material allows us to overcome this poor quantum efficiency. In fact, an electron promoted to the excited state through the absorption of one pump photon has the energetic potential to release two laser photons owing to an energy transfer toward neighboring thulium ions (
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Dates et versions

hal-01258999 , version 1 (21-01-2016)

Identifiants

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Dia Darwich, Romain Dauliat, Raphaël Jamier, Aurélien Benoit, Jean-Louis Auguste, et al.. 50.4% slope efficiency thulium-doped large-mode-area fiber laser fabricated by powder technology. Optics Letters, 2016, 41 (2), pp.384. ⟨10.1364/OL.41.000384⟩. ⟨hal-01258999⟩
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