Experimental investigations on the TMI thresholds of low-NA Yb-doped single-mode fibers

Beier, Franz; Möller, Friedrich; Sattler, Bettina; Nold, Johannes; Liem, A.; Hupel, Christian; Kühn, Stefan; Hein, Sigrun; Haarlammert, Nicoletta; Thomas, Sabu; Eberhardt, Ramona; Tünnermann, Andreas

doi:10.1364/ol.43.001291

Cited by 67 publications

(43 citation statements)

References 24 publications

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“…However, the frequency region of interest will typically not exceed 20 kHz even in high-power fiber amplifiers with smaller mode-field diameters (e.g. 20 μm), since all TMI-related beam fluctuations in fiber amplifiers reported so far occurred with frequencies below 20 kHz [5,[16][17][18].…”

Section: Pump Intensity-noisementioning

confidence: 99%

Intensity noise as a driver for transverse mode instability in fiber amplifiers

et al. 2020

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The effect of transverse mode instability (TMI) is currently the main limitation for the further average-power scaling of fiber laser systems with diffraction-limited beam quality. In this work a main driving force for TMI in fiber amplifiers is identified. Our experiments and simulations illustrate that the performance of fiber laser systems in terms of their diffraction-limited output power can be significantly reduced when the pump or seed radiation exhibit intensity noise. This finding emphasizes the fact that the TMI threshold is not only determined by the active fiber but, rather, by the whole system. In the experiment an artificially applied pump intensity-noise of 2.9% led to a reduction of the TMI threshold of 63%, whereas a similar seed intensitynoise decreased it by just 13%. Thus, even though both noise sources have an impact on the TMI threshold, the pump intensity-noise can be considered as the main driver for TMI in saturated fiber amplifiers. Additionally, the work unveils that the physical origin of this behavior is linked to the noise transfer function in saturated fiber amplifiers. With the gained knowledge and the experimental and theoretical results, it can be concluded that a suppression of pump-noise frequencies below 20 kHz could strongly increase the TMI threshold in high-power fiber laser systems.

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Section: Pump Intensity-noisementioning

confidence: 99%

Intensity noise as a driver for transverse mode instability in fiber amplifiers

et al. 2020

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“…The physics of TMI has been widely accepted but many models of TMI are still used which have some differences with respect to describing the inner workings of the instabilities [8][9][10][11]. Besides numerical models to improve the understanding and mitigation of this limitation, comprehensive experimental work has been performed to describe TMI [12][13][14][15]. Some early work utilized high-speed cameras to show transfer of power between different transverse modes [16,17] and since then the simpler photodiode (PD) method proposed by Otto et.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigations of seeding mechanisms of TMI in rod fiber amplifier using spatially and temporally resolved imaging

et al. 2020

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“…Furthermore, a constant average heat load was suggested as an indicator to predict the TMI threshold [72]. This average heat load for the TMI threshold was experimentally found in a range of 15 -34 W/m [75,116,117]. This wide range indicates that the average heat load at TMI threshold is dependent on the fibre parameters.…”

Section: Chapter 4 Power Scaling In Photodarkening Fibre By Transversmentioning

confidence: 94%

“…Two fibre lengths are considered for 95% and nearly 100% of pump absorption, respectively. A fibre length was reported to be insignificant to affect the TMI, when pump absorption above 95%, in a non-PD fibre [116]. In the following, I test this in a PD fibre.…”

Section: Fibre Lengthmentioning

confidence: 97%

“…This section examines core NA influence. I set our lowest core NA at 0.03 that is practical in the state-of-the-art fibre fabrication [116,123]. The frequency offsets with the 0.03 NA are calculated as 1070 Hz and 1050 Hz in the fibres before and after PD saturation, respectively, which are blue shifted as compared to the core NA of 0.06 (See Fig.…”

Section: Core Namentioning

confidence: 99%

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Investigation of transverse mode instability suppression in large mode area fibre

Xia¹

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In the past decades, fibre laser and amplifier systems have seen a rapid power increase due to the efficient heat dissipation and robust single-mode operation. The fibre lasers and amplifiers have become attractive sources for applications spanning from industry and defence to scientific research. In particular, the fibre lasers and amplifiers have penetrated for material processing industry including marking, cutting, welding and drilling. It had been known that the highest achievable output power in fibre laser and amplifier systems is largely limited by the nonlinear scatterings such as stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS). However, a new phenomenon under high power operation, the so-called transverse mode instability (TMI), was experimentally observed in a large mode area (LMA) ytterbium (Yb)-doped fibre amplifier in 2011. The TMI can occur much earlier than the SBS and SRS in average power scaling, hence becoming the first limitation in high-power fibre operations till now. The TMI refers to the output beam degradation, caused by the power transfer from the fundamental mode (FM) to the higher-order mode (HOM), for input pump power above a certain threshold. The origin of TMI is attributed to the stimulated thermal Rayleigh scattering x

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Experimental investigations on the TMI thresholds of low-NA Yb-doped single-mode fibers

Cited by 67 publications

References 24 publications

Intensity noise as a driver for transverse mode instability in fiber amplifiers

Intensity noise as a driver for transverse mode instability in fiber amplifiers

Experimental investigations of seeding mechanisms of TMI in rod fiber amplifier using spatially and temporally resolved imaging

Investigation of transverse mode instability suppression in large mode area fibre

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