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Author

Stefan Kuhn

Bio: Stefan Kuhn is an academic researcher from Fraunhofer Society. The author has contributed to research in topics: Ytterbium & Fiber laser. The author has an hindex of 7, co-authored 28 publications receiving 313 citations.
Topics: Ytterbium, Fiber laser, Laser cooling, Fiber, Laser

Papers
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Journal ArticleDOI
TL;DR: A high slope efficiency of 90% with diffraction-limited beam quality and without any sign of TMI or stimulated Raman scattering for a spectral dynamic range of higher than -80 dB was obtained.
Abstract: We investigate the average power scaling of two diode-pumped Yb-doped fiber amplifiers emitting a diffraction-limited beam. The first fiber under investigation with a core diameter of 30 µm was able to amplify a 10 W narrow linewidth seed laser up to 2.8 kW average output power before the onset of transverse mode instabilities (TMI). A further power scaling was achieved using a second fiber with a smaller core size (23µm), which allowed for a narrow linewidth output power of 3.5 kW limited by stimulated Brillouin scattering (SBS). We mitigated SBS using a spectral broadening mechanism, which allowed us to further increase the output power to 4.3 kW only limited by the available pump power. Up to this power level, a high slope efficiency of 90% with diffraction-limited beam quality and without any sign of TMI or stimulated Raman scattering for a spectral dynamic range of higher than -80 dB was obtained.

143 citations

Journal ArticleDOI
TL;DR: A newly designed and fabricated ytterbium-doped large mode area fiber with an extremely low NA and related systematic investigations on fiber parameters that crucially influence the mode instability threshold are reported on.
Abstract: We report on a newly designed and fabricated ytterbium-doped large mode area fiber with an extremely low NA (~0.04) and related systematic investigations on fiber parameters that crucially influence the mode instability threshold. The fiber is used to demonstrate a narrow linewidth, continuous wave, single mode fiber laser amplifier emitting a maximum output power of 3 kW at a wavelength of 1070 nm without reaching the mode-instability threshold. A high slope efficiency of 90 %, excellent beam quality, high temporal stability, and an ASE suppression of 70 dB could be reached with a signal linewidth of only 170 pm.

101 citations

Journal ArticleDOI
TL;DR: This contribution investigates the transversal mode instability behavior of a ytterbium-doped commercial 20/400 fiber and obtains 2.9 kW of output power after optimizing the influencing parameters.
Abstract: In this contribution we investigate the transversal mode instability behavior of a ytterbium-doped commercial 20/400 fiber and obtain 2.9 kW of output power after optimizing the influencing parameters. In this context, we evaluate the influence of the bend diameter and the pump wavelength within the scope of the absorption length and the length of the fiber. Furthermore, with a newly developed fiber we report on 4.4 kW of single-mode output power at 40 cm bend diameter.

56 citations

Journal ArticleDOI
TL;DR: In this article, the authors show the net cooling of high-purity Yb-doped silica glass samples that are fabricated with low impurities to reduce their parasitic background loss for fiber laser applications.
Abstract: Laser cooling of a solid is achieved when a coherent laser illuminates the material in the red tail of its absorption spectrum, and the heat is carried out by anti-Stokes fluorescence of the blue-shifted photons. Solid-state laser cooling has been successfully demonstrated in several materials, including rare-earth-doped crystals and glasses. Here we show the net cooling of high-purity Yb-doped silica glass samples that are fabricated with low impurities to reduce their parasitic background loss for fiber laser applications. The non-radiative decay rate of the excited state in Yb ions is very small in these glasses due to the low level of impurities, resulting in near-unity quantum efficiency. We report the measurement of the cooling efficiency as a function of the laser wavelength, from which the quantum efficiency of the Yb-doped silica is calculated. Laser cooling of rare-earth-doped silica may provide a route to vibration-free refrigeration of integrated photonic circuits and quantum sensors to reduce the thermal noise. Here, cooling of high-purity Yb-doped silica to 0.7 K below ambient temperature is demonstrated using sub-optimal laser parameters, and in spite of a substantial extra thermal load.

31 citations

Journal ArticleDOI
18 Mar 2021
TL;DR: More than 6 K of cooling below the ambient temperature is reported, which is the lowest temperature achieved in solid-state laser cooling of silica glass to date to the best of the authors' knowledge.
Abstract: Laser cooling of a solid is achieved when a coherent laser illuminates the material, and the heat is extracted by annihilation of phonons resulting in anti-Stokes fluorescence. Over the past year, net solid-state laser cooling was successfully demonstrated for the first time in Yb-doped silica glass in both bulk samples and fibers. Here, we report more than 6 K of cooling below the ambient temperature, which is the lowest temperature achieved in solid-state laser cooling of silica glass to date to the best of our knowledge. We present details on the experiment performed using a 20 W laser operating at a 1035 nm wavelength and temperature measurements using both a thermal camera and the differential luminescence thermometry technique.

19 citations


Cited by
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Journal ArticleDOI
TL;DR: A high slope efficiency of 90% with diffraction-limited beam quality and without any sign of TMI or stimulated Raman scattering for a spectral dynamic range of higher than -80 dB was obtained.
Abstract: We investigate the average power scaling of two diode-pumped Yb-doped fiber amplifiers emitting a diffraction-limited beam. The first fiber under investigation with a core diameter of 30 µm was able to amplify a 10 W narrow linewidth seed laser up to 2.8 kW average output power before the onset of transverse mode instabilities (TMI). A further power scaling was achieved using a second fiber with a smaller core size (23µm), which allowed for a narrow linewidth output power of 3.5 kW limited by stimulated Brillouin scattering (SBS). We mitigated SBS using a spectral broadening mechanism, which allowed us to further increase the output power to 4.3 kW only limited by the available pump power. Up to this power level, a high slope efficiency of 90% with diffraction-limited beam quality and without any sign of TMI or stimulated Raman scattering for a spectral dynamic range of higher than -80 dB was obtained.

143 citations

Journal ArticleDOI
TL;DR: The relevance of the material in high power fiber laser technologies is reviewed, and where appropriate, materials-based paths to the enhancement of laser performance will be underscored.
Abstract: Over the past two decades, fiber laser technologies have matured to such an extent that they have captured a large portion of the commercial laser marketplace. Yet, there still is a seemingly unquenchable thirst for ever greater optical power to levels where certain deleterious light-matter interactions that limit continued power scaling become significant. In the past decade or so, the industry has focused mainly on waveguide engineering to overcome many of these hurdles. However, there is an emerging body of work emphasizing the enabling role of the material. In an effort to underpin these developments, this paper reviews the relevance of the material in high power fiber laser technologies. As the durable material-of-choice for the application, the discussion will mainly be limited to silicate host glasses. The discussion presented herein follows an outward path, starting with the trivalent rare earth ions and their spectroscopic properties. The ion then is placed into a host, whose impact on the spectroscopy is reviewed. Finally, adverse interactions between the laser lightwave and the host are discussed, and novel composition glass fiber design and fabrication methodologies are presented. With deference to the symbiosis required between material and waveguide engineering in active fiber development, this review will emphasize the former. Specifically, where appropriate, materials-based paths to the enhancement of laser performance will be underscored.

138 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a review on the effect of transverse mode instability in high-power fiber laser systems and the corresponding investigations led worldwide over the past decade, including a description of the experimental observations and the physical origin of this effect.
Abstract: This work presents a review on the effect of transverse mode instability in high-power fiber laser systems and the corresponding investigations led worldwide over the past decade. This paper includes a description of the experimental observations and the physical origin of this effect, as well as some of the proposed mitigation strategies.

129 citations

01 Jan 2002
TL;DR: In this paper, the development of high power fiber lasers is reviewed, and the prospects for scaling output powers to well beyond the hundred watt level, whilst maintaining diffraction-limited beam quality are discussed.
Abstract: Recent progress in the development of high power fibre lasers will be reviewed, and the prospects for scaling output powers to well beyond the hundred watt level, whilst maintaining diffraction-limited beam quality will be discussed

124 citations

Journal ArticleDOI
TL;DR: This system represents a new average power record for thulium-doped fiber lasers (1150 W uncompressed) and ultrashort pulse fiber lasers with diffraction-limited beam quality, in general, even considering single-channel ytterbium- doped fiber amplifiers.
Abstract: In this Letter, we report on the generation of 1060 W average power from an ultrafast thulium-doped fiber chirped pulse amplification system. After compression, the pulse energy of 13.2 μJ with a pulse duration of 265 fs at an 80 MHz pulse repetition rate results in a peak power of 50 MW spectrally centered at 1960 nm. Even though the average heat-load in the fiber core is as high as 98 W/m, we confirm the diffraction-limited beam quality of the compressed output. Furthermore, the evolution of the relative intensity noise with increasing average output power has been measured to verify the absence of transversal mode instabilities. This system represents a new average power record for thulium-doped fiber lasers (1150 W uncompressed) and ultrashort pulse fiber lasers with diffraction-limited beam quality, in general, even considering single-channel ytterbium-doped fiber amplifiers.

88 citations