Optimization and Demonstration of Direct LD Pumped High-Power Fiber Lasers to Balance SRS and TMI Effects

Abstract

Up to now, transverse mode instability (TMI) and stimulated Raman scattering (SRS) have become the main factors limiting the power scaling of conventional ytterbium-doped fiber laser. Many technologies are proposed to suppress the SRS or TMI individually, but most of them are contradictions in practical application. In this article, we focus on the technologies that can balance the suppression of both SRS and TMI, including fiber coiling optimization, pump wavelength optimization, pump configuration optimization, and novel vary core diameter active fiber. Firstly, we validate the effectiveness of these technologies in both theoretical and relatively low-power experiments, and introduce the abnormal TMI threshold increasing in a few-mode fiber amplifier with fiber coiling. Then, we scale up the power through various types of fiber lasers, including wide linewidth and narrow linewidth fiber lasers, as well as quasi-continuous wave (QCW) fiber lasers. As a result, we achieve 5~8 kW fiber laser oscillators, 10~20 kW wide linewidth fiber laser amplifiers, 4 kW narrow linewidth fiber amplifiers, and 10 kW peak power QCW fiber oscillators. The demonstration of these new technical schemes is of great significance for the development of high-power fiber lasers.

Novel Bidirectional Output Ytterbium-Doped High Power Fiber Lasers: From Continuous to Quasi-Continuous

“…From the results, it can be seen that various types of BOFL face different challeng Overall, TMI and SRS are the main factors limiting the power improvement of high-pow fiber lasers. BOFL with different operating modes can achieve a balance between TMI a SRS by combining pump wavelength, pump configuration, fiber coiling, and fib structure optimization, thereby improving power [51,54].…”

“…However, the peak power of lasers that maintain near single-mode beam quality is below 3 kW, and the beam quality is relatively poor in high-power states above 3 kW. From 2022 to 2023, researchers from the University of National Defense Technology reported on high beam quality QCW fiber lasers with a power of 6–10 kW [ 49 , 50 , 51 ]. At a peak power of 10.75 kW, the beam quality remained at ~1.6 [ 51 ].…”

“…From 2022 to 2023, researchers from the University of National Defense Technology reported on high beam quality QCW fiber lasers with a power of 6–10 kW [ 49 , 50 , 51 ]. At a peak power of 10.75 kW, the beam quality remained at ~1.6 [ 51 ]. In addition, according to existing reports, QCW fiber lasers have the potential to suppress TMI.…”