![]() To some extent, tailing the gain fibers, such as confining Yb 3+ doping in the fiber core, varying core size in the longitudinal dimension, and decreasing the numerical aperture (NA) of the large mode area (LMA) fiber are theoretically and experimentally demonstrated to be capable of the effective suppression of the MI effects. By taking into different strategies, some traditional methods to mitigate the MI in high-power all-fiber laser systems are to use few-mode fibers with tight coiling, balance the heat load of a gain fiber, design the spiral winding shape of fiber, and tailor the gain fiber with high laser performance. Ī great deal of theoretical and experimental strategies has been carried out for mitigation of the MI or increasing its threshold power and SBS non-linearities in fiber laser systems. Among them, MI and SBS are the main limiting factors in the power scaling of a high-power narrow-linewidth linearly polarized MOPA system. However, a number of destructive non-linear phenomena, including stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and thermal mode instability (MI), can jeopardize the stability of the laser system because of the high intensity in the fiber core. ![]() High-power narrow-linewidth fiber lasers or amplifiers with linearly polarized have been a major area of interest within the field of gravitational wave detection (GWD), non-linear frequency conversion (NFC), spectral beam combining (SBC), coherent beam combining (CBC), and ultrafast lasers, etc., Over the last decade, ytterbium (Yb)-doped master oscillator power amplifiers (MOPAs) with linearly polarized ones have made great progress, and the power scaling has reached the muti-kilowatt level. By applying the MI suppression method, a double-eight-shaped aluminum plate was adopted to coil the gain fiber, and the MI threshold increased by more than 1100 W. ![]() Increasing the seed linewidth from 0.0454 nm to 0.0976 nm by adding 200 m polarization maintaining Ge-doped fiber the stimulated Brillouin scattering threshold increased from 805 W to above 3.2 kW. And the results reveal that the MI threshold is enhanced by more than 370 W for every 0.004 decrease in core numerical aperture. By examining various numerical aperture (NA) PMYDFs, the experimental investigation on expanding mode instability (MI) threshold in PM fiber amplifiers was put on display. In this work, a narrow-linewidth linearly polarized fiber amplifier with a record output power of 3.2 kW was achieved based on a homemade polarization-maintaining Yb-doped fiber corresponding to a slope efficiency of 79% and a 3 dB linewidth of 0.2227 nm. Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China.Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law.Shibiao Liao Tao Luo Runheng Xiao Junjie Cheng Chang Shu Zhilun Zhang Yanyan Zhou Yingbin Xing* Haiqing Li Jinggang Peng Nengli Dai Jinyan Li One print or electronic copy may be made for personal use only. The paper can be found at the following official DOI. This paper was published in Optics Letters and is made available as an electronic reprint (preprint) with permission of Optical Society of America. School of Physical and Mathematical Sciences ![]() Ten watts of CW Ho:YAG laser power was generated with >96% coherent combining efficiency. Increased single-pass absorption, suppression of output power saturation, and improvement in beam quality were shown using the coherent polarization locking technique as compared to a conventional Ho:YAG laser cavity with the same pump and cavity configuration. We overcome several thermal issues present in Ho:YAG lasers by distributing the gain over a larger volume and achieve a diffraction-limited beam using coherent polarization locking. Preserving a diffraction-limited beam in Ho:YAG laser using coherent polarization locking. Preserving a diffraction-limited beam in Ho:YAG laser using coherent polarization locking
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