Jinyan Li’s research while affiliated with Huazhong University of Science and Technology and other places

Correction for ‘Analysis of ion doping profiles in Yb-doped fiber preforms using laser-induced breakdown spectroscopy’ by Jiaming Li et al. , J. Anal. At. Spectrom. , 2016, 31 , 492–496, DOI: 10.1039/C5JA00429B.

The radical elimination of photodarkening effect by H2-loading was demonstrated, and the output power was stable during long term operation in high power fiber amplifiers, without mode instability and photodarkening-induced core laser leakage.

This study reports the radical elimination of the photodarkening (PD)-effect in Yb-doped fiber through deuterium loading. With deuterium pre-loading, no PD-induced excess loss of the Yb-doped fiber was observed under 915-nm pumping conditions. Moreover, the existing loss induced by the PD effect was also eliminated via deuterium loading, and the excess loss declined to nearly 0 dB/m. The method was also validated in a KW-level fiber laser experimental setup. In the 20/400-μm deuterium pre-loaded Yb-doped fiber, an output laser power of 1630 W and beam quality factor (M ² ) of 1.69 were obtained. The two parameters remained stable during the entire continuous operation process of 40 min, and displayed very little power fluctuation of <0.5%. The results of our experiments confirmed that deuterium loading can protect Yb-doped fibers from the PD effect, thereby improving the power and mode stability, which is often deteriorated by PD. Notably, the results of this study are beneficial in terms of further development of high-power fiber lasers.

In this work, we proposed a nanoporous glass phase-separation method to fabricate low photo-darkening Yb-doped fiber. Compared to a modified conventional vapor deposition method, equilibrium photo-darkening induced excess loss at 702, 810, and 1041 nm of the nanoporous glass fiber was reduced to 35.07, 12.49 and 1.69 dB/m, respectively, despite higher Yb³⁺ concentration. The excess loss mitigation percentage was above 20%, and about 1 dB/m self-bleaching was observed. Besides, slope efficiency of this fiber was measured to be as high as 72.8%. The mechanism of photo-darkening mitigation by the porous glass phase-separation technology was also discussed. The results strongly confirmed that the method is applicable to further develop high-power fiber lasers with low photo-darkening effect.

In this work, we systematically studied the mitigation of photodarkening (PD) in ytterbium-doped silica fiber co-doped with lithium (Li). Adding a proper concentration of Li⁺ ions to the core glass composition, the PD-induced excess loss can be reduced by 25%. The results showed that the effect on numerical aperture and laser efficiency was very small. Compared with the sodium (Na) co-doped Yb/Al silica fiber at the same concentration, the mitigation of the PD effect through Li⁺ and Na⁺ ions co-doping was analyzed and discussed. Furthermore, a hypothesis was proposed for the mechanism of alkali metal Li and Na co-doping to mitigate the PD effect. More effective core composition and doping concentration were proposed to provide guidance of high output power gain fiber preparation.

Ytterbium-doped fibers have become the optimum gain media of high-power fiber lasers thanks to a simple energy structure, which strongly reduces the excited state absorption, and a low quantum defect and a high optic–optic conversion efficiency, which means the low thermal load. In this paper, we take a review of the current state of the art in terms of $\text{Yb}^{3+}$ doped fibers for high-power fiber lasers, including the development of the fabrication techniques. The research work to overcome the challenges for $\text{Yb}^{3+}$ doped fibers, which affect the stability of output power and beam quality, will be demonstrated. Direction of further research is presented and the goal is to look for a fiber design, to boost single fiber output power, stabilize the laser power and support robust single-mode operation.

Ion doping profiles are one of the most important characteristics in Yb-doped fibers, but it is difficult to realize rapid, in situ, and online analysis. A laser-induced breakdown spectroscopy (LIBS) system was set up to analyze ion doping profiles in Yb-doped fiber preforms. However, laser-induced irregular cracking occurred on the preform surfaces and generated outliers in the Yb maps that affected the analytical results. An algorithm of a self-adaptive median filter (SAMF) was introduced to modify the maps. The results of LIBS mapping assisted by SAMF clearly described the doping profiles of a step-wise and a central dip. The energy dispersive X-ray spectroscopy (EDS) and the X-ray fluorescence (XRF) techniques were used to validate the analytical results. This study provides a rapid, in situ, and online approach for analysis of ion doping profiles in Yb-doped fibers.