• High Power Laser Science and Engineering
  • Vol. 9, Issue 3, 03000e45 (2021)
Pengfei Ma, Hu Xiao, Wei Liu, Hanwei Zhang, Xiaolin Wang, Jinyong Leng, and Pu Zhou*
Author Affiliations
  • College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha410073, China
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    DOI: 10.1017/hpl.2021.32 Cite this Article
    Pengfei Ma, Hu Xiao, Wei Liu, Hanwei Zhang, Xiaolin Wang, Jinyong Leng, Pu Zhou. All-fiberized and narrow-linewidth 5 kW power-level fiber amplifier based on a bidirectional pumping configuration[J]. High Power Laser Science and Engineering, 2021, 9(3): 03000e45 Copy Citation Text show less

    Abstract

    In this paper, an all-fiberized and narrow-linewidth 5 kW power-level fiber amplifier is presented. The laser is achieved based on the master oscillator power amplification configuration, in which the phase-modulated single-frequency laser is applied as the seed laser and a bidirectional pumping configuration is applied in the power amplifier. The stimulated Brillouin scattering, stimulated Raman scattering, and transverse mode instability effects are all effectively suppressed in the experiment. Consequently, the output power is scaled up to 4.92 kW with a slope efficiency of as high as approximately 80%. The 3-dB spectral width is about 0.59 nm, and the beam quality is measured to be M2∼1.22 at maximum output power. Furthermore, we have also conducted a detailed spectral analysis on the spectral width of the signal laser, which reveals that the spectral wing broadening phenomenon could lead to the obvious decrease of the spectral purity at certain output power. Overall, this work could provide a reference for obtaining and optimizing high-power narrow-linewidth fiber lasers.

    1 Introduction

    High-power narrow-linewidth fiber lasers with excellent beam quality have been highly desired for spectral and coherent beam combinations[1-3]. The power scaling of single-mode narrow-linewidth fiber lasers has been under intense investigation[4-15]. This mainly involves comprehensive suppressions of the transverse mode instabilities (TMIs) and nonlinear inelastic scattering effects, such as stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS)[16-18]. Basic principles to increase the TMI and SBS/SRS thresholds in high-power fiber lasers have already been proposed based on the understanding of those effects[19-20]. Specifically, the TMI effect could be suppressed through reducing the strength of the thermally induced index grating, manipulating the phase shift between the thermally induced refractive index grating and the modal interference pattern, and decreasing the relative gain of the higher-order modes (HOMs)[19]. The SBS/SRS effects could be suppressed through reducing the effective fiber length or the effective Brillouin/Raman gain coefficient[20]. Those principles could be fulfilled mainly through special design of active fiber or optimization of the structure and parameters of fiber amplifiers. As for the fiber design, a near single-mode fiber laser with an output power of 3 kW and spectral linewidth of 12 GHz has been achieved based on gold-coated specialty gain fiber[5], and a single-mode fiber laser with an output power of 3.5 kW and spectral linewidth of 0.18 nm has been achieved based on low-numerical aperture (NA) low-mode-area (LMA) gain fiber[6]. It should be noted that those two fiber laser systems are established in free-space structure, which is not suitable for compact assembling and maintenance. Therefore, most of the reported all-fiberized narrow-linewidth fiber amplifiers are based on conventional active fiber and require comprehensive optimization of structure and parameters of the fiber amplifiers[7-15]. As for all-fiberized format, 3.7-kW output power has been achieved with near-diffraction-limited beam quality and spectral linewidth of approximately 0.3 nm[15].

    Copy Citation Text
    Pengfei Ma, Hu Xiao, Wei Liu, Hanwei Zhang, Xiaolin Wang, Jinyong Leng, Pu Zhou. All-fiberized and narrow-linewidth 5 kW power-level fiber amplifier based on a bidirectional pumping configuration[J]. High Power Laser Science and Engineering, 2021, 9(3): 03000e45
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