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Contents Letters, 4 Article(s)
Greater than 2 kW all-passive fiber Raman amplifier with good beam quality
Yizhu Chen, Tianfu Yao, Hu Xiao, Jinyong Leng, and Pu Zhou

We report a 2 kW all-fiberized Raman fiber amplifier with efficient brightness enhancement based on the graded-index fiber. The maximum power output reaches up to 2.034 kW centered at 1130 nm, with a conversion efficiency of 79.35% with respect to the injected pump power. To the best of our knowledge, this is the highest conversion efficiency obtained for any Raman laser system using graded-index fiber. An optimized fiber combiner adopting graded-index fiber as the pigtail fiber was fabricated, enabling the preservation of the seeding brightness in the core-pumped Raman fiber amplifier, and further enhancing the ultimate brightness of the output laser after amplification. At the maximum power output, the beam quality parameter M2 is 2.8, corresponding to a signal-to-pump brightness enhancement factor of 11.2. As far as we know, we obtain the highest brightness enhancement among Raman fiber lasers of over 100 W, and the best beam quality for graded-index Raman fiber lasers of over 150 W.

High Power Laser Science and Engineering
Jan. 01, 1900, Vol. 8 Issue 4 04000e33 (2020)
Mid-infrared optical frequency comb in the 2.7–4.0 μm range via difference frequency generation from a compact laser system
Lian Zhou, Yang Liu, Gehui Xie, Chenglin Gu, Zejiang Deng, Zhiwei Zhu, Cheng Ouyang, Zhong Zuo, Daping Luo, Bin Wu, Kunfeng Chen, and Wenxue Li

We report on the generation of a mid-infrared (mid-IR) frequency comb with a maximum average output power of 250 mW and tunability in the 2.7–4.0 μm region. The approach is based on a single-stage difference frequency generation (DFG) starting from a compact Yb-doped fiber laser system. The repetition rate of the near-infrared (NIR) comb is locked at 75 MHz. The phase noise of the repetition rate in the offset-free mid-IR comb system is measured and analyzed. Except for the intrinsic of NIR comb, environmental noise at low frequency and quantum noise at high frequency from the amplifier chain and nonlinear spectral broadening are the main noise sources of broadening the linewidth of comb teeth, which limits the precision of mid-IR dual-comb spectroscopy.

High Power Laser Science and Engineering
Jan. 01, 1900, Vol. 8 Issue 4 04000e32 (2020)
35 W continuous-wave Ho:YAG single-crystal fiber laser
Yongguang Zhao, Li Wang, Weidong Chen, Jianlei Wang, Qingsong Song, Xiaodong Xu, Ying Liu, Deyuan Shen, Jun Xu, Xavier Mateos, Pavel Loiko, Zhengping Wang, Xinguang Xu, Uwe Griebner, and Valentin Petrov

We report on a high-power Ho:YAG single-crystal fiber (SCF) laser inband pumped by a high-brightness Tm-fiber laser at 1908 nm. The Ho:YAG SCF grown by the micro-pulling-down technique exhibits a propagation loss of $0.05\pm 0.005~\text{cm}^{-1}$ at $2.09~\unicode[STIX]{x03BC}\text{m}$. A continuous-wave output power of 35.2 W is achieved with a slope efficiency of 42.7%, which is to the best of our knowledge the highest power ever reported from an SCF-based laser in the 2 $\unicode[STIX]{x03BC}\text{m}$ spectral range.

High Power Laser Science and Engineering
Jun. 23, 2020, Vol. 8 Issue 2 02000e25 (2020)
Pushing the boundaries of diode-pumped solid-state lasers for high-energy applications
Saumyabrata Banerjee, Paul Mason, Jonathan Phillips, Jodie Smith, Thomas Butcher, Jacob Spear, Mariastefania De Vido, Gary Quinn, Danielle Clarke, Klaus Ertel, Cristina Hernandez-Gomez, Chris Edwards, and John Collier

We report on the successful demonstration of a 150 J nanosecond pulsed cryogenic gas cooled, diode-pumped multi-slab Yb:YAG laser operating at 1 Hz. To the best of our knowledge, this is the highest energy ever recorded for a diode-pumped laser system.

High Power Laser Science and Engineering
May. 21, 2020, Vol. 8 Issue 2 02000e20 (2020)
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