A novel fiber laser oscillator employing saddle-shaped core ytterbium-doped fiber
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A novel fiber laser oscillator employing saddle‑shaped core ytterbium‑doped fiber Lingfa Zeng1 · Xiaoming Xi1,2,3 · Yun Ye1 · Xianfeng Lin4 · Xiaolin Wang1,2,3 · Jinyan Li4 · Chen Shi1,2,3 · Baolai Yang1,2,3 · Hanwei Zhang1,2,3 · Peng Wang1,2,3 · Pu Zhou1,2,3 · Xiaojun Xu1,2,3 Received: 30 May 2020 / Accepted: 7 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract A novel high-power fiber laser oscillator employing a saddle-shaped core ytterbium-doped fiber (SSCYDF) is proposed and demonstrated experimentally. The SSCYDF is designed and fabricated with a long-tapering core (diameter of ~ 30 µm at both ends and ~ 23 µm in the middle) and a constant inner cladding (diameter of ~ 400 µm) in longitudinal dimension. On the one hand, the small core section of the fiber can only support less than two modes, which is helpful for the mitigation of the transverse mode instability. On the other hand, the large core section provides a large mode area for suppression of stimulated Raman scattering. Therefore, this type of laser oscillator holds the potential advantages for both mitigation of transverse mode instability and suppression of stimulated Raman scattering. Based on the homemade SSCYDF, an all-fiber laser oscillator is constructed and investigated by pumping with laser diodes at wavelength of 976 nm and 915 nm, respectively. The maximum output power of 1312 W is achieved in the case of co-pumping at 915 nm. This is the first work, to the best of our knowledge, to validate the feasibility of using saddle-shaped core ytterbium-doped fiber with constant cladding for high-power fiber lasers. Keywords Fiber laser oscillator · Saddle-shaped core fiber · Transverse mode instability
1 Introduction Recent research on high-power fiber lasers shows that transverse mode instability (TMI) and stimulated Raman scattering (SRS) have become the main limiting factors for power scaling [1–3]. Many efforts have been made to conquer the Lingfa Zeng and Xiaoming Xi co-first author. * Xiaolin Wang [email protected] * Jinyan Li [email protected] 1
College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China
2
State Key Laboratory of Pulsed Power Laser Technology, Changsha 410073, China
3
Hunan Provincial Key Laboratory of High Energy Laser Technology, Changsha 410073, China
4
School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China
limitation of the TMI and SRS, such as specially designed large-mode-area (LMA) fibers [4, 5], fiber coiling [6, 7] and temporal modulation of the pump source [8]. However, there is sharp contradiction in the suppression of TMI and SRS. In 2018, Yang et al. reported a fiber laser oscillator based on a ytterbium-doped fiber (YDF) with a core/cladding diameter of about 21/400 μm and a laser output of 3.05 kW with a beam quality of about 1.3 was achieved [9]. The Stokes intensity at the highest power is 29 dB lower than the signal, and the power increa
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