Article

# Ytterbium-doped large-core fiber laser with 1.36 kW continuous-wave output power

University of Southampton, Southampton, England, United Kingdom
(Impact Factor: 3.53). 01/2005; 12(25):6088-92. DOI: 10.1364/OPEX.12.006088
Source: PubMed

ABSTRACT We have demonstrated a highly-efficient cladding-pumped ytterbium-doped fiber laser generating 1.36 kW of continuous-wave output power at 1.1 mum with 83% slope efficiency and near diffraction-limited beam quality. The laser was end-pumped through both fiber ends and showed no evidence of roll-over even at the highest output power, which was limited only by available pump power.

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##### Article: Polarization Effects on Thermal-Induced Mode Instabilities in High Power Fiber Lasers
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ABSTRACT: We present detailed studies of the effect of polarization on thermal-induced mode instability (MI) in ytterbium-doped fiber amplifiers. Based on a steady-state theoretical model, which takes both electric fields along the two principal axes into consideration, the effect of polarization effects on the gain of Stokes wave was analyzed, which shows that the polarization characteristics of the fiber laser have no impact on the threshold of MI. Experimental validation of the theoretical analysis is presented with experimental results agreeing well with the theoretical results, in which polarization-maintained and non-polarization-maintained fiber lasers with core/inner cladding diameter of 30/250um and core NA of 0.07 were employed. The MI threshold power is measured to be about 367~386W.
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##### Article: Influences of pump transitions on thermal effects of multi-kilowatt thulium-doped fiber lasers
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ABSTRACT: Thermal effects are critical constrains for developing high-power thulium-doped fiber lasers (TDFLs). In this paper, we numerically investigate the lasing and thermal characteristics of the TDFLs under different pump transitions. Our results show, the widely-used pump transition $^3H_6\rightarrow^3H_4$, taking advantages of high-power high-efficiency laser diodes at $\sim$0.8 $\mu$m, may not be a superior choice for directly outputting multi-kilowatt at 2 $\mu$m because of severe thermal problems. Meanwhile, using other pump transitions resulting 2-$\mu$m emissions, especially the in-band pump transition $^3H_6\rightarrow^3F_4$, will decrease the generated heat to a large extent. By optimizing the power filling factor of the gain fiber, we find a 2-$\mu$m TDFL cladding-pumped at 1.9 $\mu$m will lead to the laser slope efficiency close to its quantum efficiency (95\%). The induced ultra-low quantum defect would be of great importance for power scaling. We thus propose tandem-pumped TDFLs for reducing the heat at high powers and discuss the related issues of design. Besides, we also explore the differences of the thermal characteristics between laser and superfluorescent operations, which will contribute to deepening the understanding of the thermal effects in high-power thulium-doped fiber amplifiers.
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