Research On The Anti-photon Darkening Performance Of Yb/Ce Co-doped Aluminum-silicon Binary System Fiber

As a new generation of laser devices,fiber lasers are widely used in national defense military,industrial processing,biomedical,optoelectronic communication and many other fields because of their unique advantages such as small size,light weight,simple and compact structure,high pumping eniciency,good beam quality,high reliability and maintenance-free.Recently,the application requirements of high-power lasers in various fields are increasingly strong.However,the mechanisl of photodarkening effect,which is one of the main factors hindering the improvement and stability of laser output power,has not been fully explained.The existing research is not enough to solve the power attenuation and the reduction of optic-to-optic conversion efficiency for high-power large-mode-area active fiber naterials under long-time laser output.This paper focuses on the key technologies of the Yb/Ce co-doped aluminosilicate laser fiber materials,and carries out the mechanism research and comprehensive performance for properties of the photodarkening resistance based on kw-level high-power fiber lasers:Firstly,this paper introduces the current mechanism model for the photodarkening caused by photon irradiation and its suppression method.Secondly,based on the measures of changing the fiber material composition to suppress photodarkening phenomenon,the advantages and disadvantages of Yb-AlSi,Yb-PSi,Yb-AlPSi and Yb/Ce-AlSi fibers are comprehensively compared.The laser output stability test was carried out on the home-made 20/400-Yb-AlSi binary fiber and 20/400-Yb-AlPSi temai*y fiber.The results showed that the photodarkening resistance of Yb-AlPSi fiber was obviously better than that of Yb-AlSi fiber,but it is easy to produce central depression and refractive index fluctuation due to the difficulties in perfonn preparation of Yb-AlPSi fiber.In this paper,the Yb/Ce co-doped aluminumsilicate binary fiber with less difficulties in fabrication and good photodarkening resistance performance was selected and designed.Thirdly,the element species and concentration of the dopants are fomiulated to design the fiber material composition,so that the optical fiber material has photodarkening resistance perfonnance while satisfying the requirement of low numerical aperture of double-clad large-mode-area silicate fiber.F element was doped to counteract the increase in the refractive index of the fiber caused by the doping of Yb,Ce,Al,and also to resist radiation.The Yb/Ce co-doped AlFSi binaiy fiber was used as the target sample.Cerium/ytterbium ions ratio of 0.5 was specially designed to mitigate photodarkening and reduce the thermal load caused by Ce doping.The Al/F ion concentration ratio was set to be 1 to ensure that the core numerical aperture of fiber was in the range of 0.065±0.05,satisfying high power application background for large-mode-area fiber.Next,the fabrication principle and parameter setting of the method combining the modified chemical vapor deposition technology with chelate precursor doping technique are introduced.Using this method,the Yb/Ce co-doped AIFSi binary fiber preform was successfully fabricated and drawn into 20/400 fiber sample.Finally,static parameters and dynamic laser performance tests were performed on Yb/Ce-AlSi fibers.The results showed that the core numerical aperture of fiber was 0.0602,the doping concentrations of Yb₂O₃,Ce₂O₃,Al₂O₃ and SiF₄ were 0.12mol%,0.05mol%,0.5mol%and 0.2mol%respectively,satisfying the design requirements of the concentration ratio of Ce/Yb??0.5?and Al/F??1?.Under master oscillating power amplification system,the output power was 1930W and optic-to-optic conversion efficiency was 79.2%.When the laser is turned on at 1850W for 540 minutes,the laser power fluctuation was less than 1.04%,verifying there was no photodarkening phenomenon.