Preparation Of Rare Earth Doped AlF₃-based And InF₃-based Glass Fibers For Mid-infrared Laser

3～5μm mid-infrared fiber lasers have significant applications in remote sensing communication,medical treatment,spectroscopy,environmental monitoring,national defense security,and other fields.Rare earth ion doped fiber lasers are the main ways to obtain laser output in this region.At present,lasers in 3～4μm band have been obtained with erbium-(Er³⁺),holmium-(Ho³⁺),and dysprosium-(Dy³⁺)doped fluoride fibers.And the output power of～3μm laser based on Er³⁺doped ZBLAN glass fiber has exceeded 40 W.However,due to the deliquescence and low glass transition temperature of ZBLAN glass,the fiber surface is easy to be damaged during the lasing operation,especially in a high-power system.Therefore,it limits the stability and output power improvement of the mid-infrared lasers.In addition,the laser efficiency and output power of some bands（e.g.～3.3μm and～4μm）are still backward.To solve these problems,during the Ph.D,the author focused on the design and preparation of rare earth ion doped fluoride glass fiber with good thermal stability,good water resistance and low phonon energy;the improvement of laser performance of～2.9μm Ho³⁺-doped Al F₃ based glass fiber,and exploration of new ways to obtained efficient～3.3μm and～4μm lasers.The main achievements are as follow:（1）Efficient～2.9μm lasing with a slope efficiency of 15.3%was obtained based on the Ho³⁺/Pr³⁺co-doped fiber.Firstly,the Ho³⁺/Pr³⁺co-doped Al F₃ based glass samples were prepared by melting method.The effect of Pr³⁺doping concentration on the～2.9μm luminescence properties of the samples was analyzed.The experimental results showed that the luminescence enhancement of～2.9μm could be obtained through the energy transfer processes(Ho³⁺:⁵I₇→Pr³⁺:³F₂,³H₆ and Pr³⁺:¹G₄→Ho³⁺:⁵I₆)between Ho³⁺and Pr³⁺ions.Then,Ho³⁺/Pr³⁺co-doped fiber was fabricated by rod-in-tube method.The～2.9μm laser was obtained from the fiber.When Ho³⁺/Pr³⁺concentration was 1.5 mol%/0.2 mol%,the maximum output power was 189 m W,with a slope efficiency of 15.3%,which was three times as high as that of only Ho³⁺doped condition（5.1%）.Our results showed that Ho³⁺/Pr³⁺co-doped Al F₃ based glass fibers can be used to construct high-efficiency～2.9μm fiber lasers.（2）Er³⁺doped fluoroindate glass fiber was designed and fabricated,and intense emission at～3.3μm was obtained for the first time,corresponding to the transition⁴S_3/2→⁴F_9/2 of Er³⁺ions.Er³⁺doped fiber with low loss was fabricated with rod-in-tube method by using low-phonon-energy(～510 cm^-1)In F₃ based glass as the matrix material.Based on the Er³⁺doped In F₃ based glass fiber,intense emission at～3.3μm was observed pumped by a 976 nm laser diode.The experimental results showed that the emission came from the transition ⁴S_3/2→⁴F_9/2 of Er³⁺ions.The stimulated emission cross-section at～3.3μm was～3×10^-26 m²,which was～1.5 times larger than that of transitions Er³⁺:⁴F_9/2→⁴I_9/2 and Dy³⁺:⁶H_13/2→⁶H_15/2.In addition,a broad emission ranging from 3.1μm to 3.85μm was obtained from the Er³⁺doped fiber under a 976nm/1973 nm dual-wavelength pumping scheme.Our results indicated that Er³⁺doped fluoroindate glass fibers had the potential for constructing efficient～3.3μm,and broadband tunable mid-infrared fiber lasers covering 3.1～3.85μm band.（3）Pr³⁺/Yb³⁺co-doped fluoroindate glass was designed and prepared.Intense emission at～4μm was obtained under 976 nm pumping.Pr³⁺/Yb³⁺co-doped fluoroindate glass was prepared by melting method.The～4μm emission from Pr³⁺:³F₄→³H₆ transition was observed by using a 976 nm laser diode as the pump source.The stimulated emission cross section at～4μm was 1.44×10^-24 m²,which was almost4 times larger than that of Ho³⁺:⁵I₅→⁵I₆ transition in In F₃-based fiber.In addition,we also observed the emissions at～3μm and～3.56μm,corresponding to the transitions¹G₄→³F₃ and ¹G₄→³F₄ of Pr³⁺ions.And the emission spectrum could cover the wavelength range of 2.6～4.4μm.Our results showed that Pr³⁺/Yb³⁺co-doped In F₃based glass had the potential for constructing high-efficiency～4μm fiber laser and wide tunable laser covering 2.6～4.4μm band.