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chi20190524上海光机所胡丽丽557596Ytterbium-doped silica fiber (YDF) laser is a very appealing technology to implement space communication, laser radar, space trash disposal and space laser weapon, owing to its reduced weight, size, high electronic-optic efficiency, high peak power combined with narrow pulse width. However, the YDF will suffer from a harsh ionizing radiation (such as proton, electron, X- and γ-ray) during their space mission. The radiation-induced darkening (RD) effect can lead to an obvious increase in fiber loss and a drastic decrease in laser slope efficiency, and even no laser output in severe cases. This dissertation is focused on the mechanism research of RD in YDF. The ytterbium doped silica glasses (YDGs) co-doped with different elements (Al, P, Ce, F et al.) were the main research objects and prepared by using sol-gel combining high temperature sintering method. The fictive temperature (Tf) of YDG was changed by thermal annealing pre-treatment at different temperatures and atmospheres. The effects of glass compositions and Tf on the spectral properties of YDGs before and after radiation were systematically studied. The RD mechanism will be revealed from the dynamic evolutions of atomic level micro-structures and defects by combining the pulsed and continuous wave (CW) electron paramagnetic resonance (EPR), solid-state nuclear magnetic resonance (NMR) and other modern structural research methods. The aim is to obtain the optimum glass composition and pretreatment scheme, to establish the radiation induced defect generation and annihilation model, and to provide theoretical basis and solution for the development of YDF with high laser performance and high radiation resistance. Based on these researches, a super radiation-resistive double cladding YDF with 20 μm core and 400 μm inner cladding diameters was successfully prepared by modified chemical vapor deposition (MCVD) combined with high temperature drawing. And the laser behaviors of this YDF before and after gamma radiation will be compared. This dissertation is constituted by six chapters. Chapter I is literature review. Chapter II is theoretical basis and experimental methods. Chapters III, IV and V are the main research contents of this dissertation. The summarizes and prospects are given in Chapter VI. The main contents of each chapter are as follows: In Chapter I, the literature review introduces the research background of radiation-resistant optical fibers, the factors affecting the radiation sensitivity of optical fibers, the methods to improve the radiation resistance of optical fibers, and the mechanism of RD in optical fibers. Based on the drawbacks of available RD mechanism in active fibers, the research ideas and primary research content of this dissertation are put forward. In Chapter II, the network structure and radiation induced defects in pure silica glass, Al3+, P5+, F- single-doped silica glasses are presented. The basic theories of EPR and NMR are introduced. The preparation methods, treatment conditions and characterization methods of glass and optical fiber samples are described. In Chapter III, the effects of single-doping or co-doping of aluminum and phosphorus on the structure, spectral properties and radiation resistance of YDGs were systematically studied. The results show that the ultraviolet absorption of YDGs primarily originates from the charge-transfer (CT) transition from O2– to Yb3+. The location of CT absorption is associated with the local structure of Yb3+ ions. The CT bands located at 6.3, 5.8 and 5.2 eV correspond to Yb-O-P, Yb-O-Si and Yb-O-Al linkages, respectively. Excitation to CT bands results in the formation of Yb2+ ions and oxygen hole centers (OHCs) pairs. The corresponding chemical reaction can be expressed as follows: Yb^(3+)-O-R≡ ?〖 Yb〗^(2+)+ ■(°O-R≡@(R-OHC) ) (R=Al,Si,P) The structure and radiation induced color centers of YDGs are significantly affected by the P/Al co-doping ratio. When P/Al < 1, Yb3+ ions are primarily surrounded by [SiO4/2]0 and [AlO4/2]- groups, Yb3+ and [AlO4/2]- capture electron and hole during radiation, respectively, leading to the formations of Yb2+ and Al-OHC color centers; when P/Al > 1, Yb3+ ions are primarily surrounded by [O=PO3/2]0 (that is P(3) groups). The P=O double bond in P(3) group is easily ionized during radiation, resulting in the formation of phosphorus-related color centers (P1, P2, P-OHC); when P/Al=1, Yb3+ ions are only surrounded by [AlPO4]0 groups. [AlPO4]0 is difficult to gain and lose electrons during radiation. Therefore, the radiation resistance of YDG can be improved to some extent by co-doping aluminum and phosphorus. In Chapter IV, the effects of annealing temperature, annealing atmosphere and fluorine content on the structure, spectral properties and radiation resistance of YDGs were systematically studied. The results show that planar three-ring (D2) and planar four-ring (D1) are the precursors of Si-E′ and NBOHC, the four-coordinated aluminum (AlIV) is the precursor of Al-OHC. When the structure relaxation of Yb3+-single doped silica glass reaches equilibrium state, the fictive temperature (Tf) of glass equals to its annealing temperature. The smaller Tf, the less D1 and D2 groups and the better radiation resistance in Yb3+-single doped silica glass. Annealing in hydrogen atmosphere can promote the structural relaxation, reduce the content of D1, D2 and AlIV groups, increase the content of low-valent rare earth ions (Ce3+, Yb2+), and significantly improve the radiation resistance of Yb3+/Al3+/Ce3+-doped silica glasses. Co-doping with fluorine can also promote the structural relaxation, reduce the content of D1, D2 and AlIV groups, and improve the radiation resistance of Yb3+/Al3+/Ce3+/F--doped silica glasses. In Chapter V, the effects of radiation conditions, core compositions and pre-treatment methods on the radiation resistance of YDFs were systematically studied. The results show that the radiation induced loss (RIA) in YDF is very sensitive to the total dose and dose rate of radiation, but not sensitive to the type of radiation source (X- or γ-ray). Under the same radiation conditions, the RIA values in Yb3+/Al3+/F- co-doped silica fibers decrease step by step with the addition of P5+ and Ce3+. Loading with hydrogen (H2) and deuterium (D2) can significantly improve the radiation resistance of YDFs, but the disadvantage is that H2 or D2 molecules can easily diffuse out of the fibers, leading to the failure of the radiation resistance of the fibers. The thermal annealing in D2 atmosphere for the YDF preform prepared by MCVD can significantly improve the radiation resistance of YDF, and has no obvious negative impact on the optical loss and laser slope efficiency in non-radiated YDF. After 700 Gy γ-radiation, the laser slope efficiency of this fiber decreases by only 28% (72%→52%). The radiation resistance of this fiber can fully meet the total dose requirement for the YDF laser serving in geosynchronous orbit for seven years (< 500 Gy). In Chapter VI, the main experimental results, innovations and insufficiencies of this dissertation are summarized. The suggestions for future research are given.2019atalunwen219621525694Yb3+-doped silica glass, structure and defects, radiation resistant optical fibers, spectrum and laser properties, structural relaxationStudy on structure, spectrum, radiation resistance and radiation-induced darkening mechanism of Yb3+-doped silica glasses掺Yb3+石英玻璃的结构、光谱与耐辐照性能及辐致暗化机理研究掺镱(Yb3+)石英光纤激光器具有重量轻、体积小、电光转换效率高、峰值功率高、线宽窄等优势,在空间通讯、激光雷达、太空垃圾处理、机载激光武器等方面具有重要应用价值。然而,激光器在执行太空任务时,将面临恶劣的粒子辐射(如质子、电子、X射线和γ射线)。粒子辐射会导致激光器内有源光纤的损耗急剧增加,激光斜率效率大幅下降,严重时甚至没有激光输出,这种现象称为辐致暗化效应。本论文以掺Yb3+石英光纤的辐致暗化机理研究为主线。以掺Yb3+石英玻璃为主要研究对象。采用溶胶凝胶(Sol-Gel)结合真空烧结法制备含不同共掺元素(Al、P、F、Ce)的掺Yb3+石英玻璃;在不同温度、不同气氛下对掺Yb3+石英玻璃进行热退火预处理,目的是改变玻璃的假想温度(Tf);采用193 nm 准分子激光器、X射线、γ射线作为辐照源。系统研究玻璃组分和假想温度对辐射前后掺Yb3+石英玻璃光谱性质的影响,并结合电子顺磁共振(EPR)、固态核磁共振(NMR)等现代结构研究手段从原子级结构、缺陷的演变角度揭示其影响机理。目的是获得优化的玻璃组分和预处理方案;建立辐射诱导缺陷产生与湮灭模型;为研制高性能、耐辐射的掺Yb3+石英光纤提供理论依据和解决方案。在上述玻璃研究基础上,采用改进的化学气相沉积(MCVD)法结合高温拉丝工艺成功制备出一种双包层20/400 μm规格的超强抗辐射掺Yb3+石英光纤,并比较研究了这种光纤辐射前后的激光性能。 本论文包含六章:第一章和第二章为介绍部分,主要介绍了课题的研究背景、研究现状、相关理论基础及实验方法。第三章至第五章为本论文的主要研究内容。第六章对全文进行总结和展望。下面简要介绍各个章节的主要内容: 第一章介绍了耐辐射光纤的研究背景,影响光纤辐射敏感性的因素,提高光纤抗辐射特性的方法,以及光纤出现辐致暗化的机理。针对现有有源光纤的辐致暗化机理研究不足,提出本论文的研究思路和研究内容。 第二章介绍纯石英和Al3+、P3+、F-单掺石英玻璃的网络结构及辐射诱导缺陷;EPR和NMR基本理论;玻璃和光纤样品的制备方法、处理条件、及测试表征方法。 第三章系统研究了铝、磷单掺或共掺对掺Yb3+石英玻璃结构、光谱性质和耐辐射性质的影响。研究表明掺Yb3+石英玻璃的紫外吸收主要起源于O2-→Yb3+电荷迁移(CT)跃迁。CT吸收的位置与Yb3+的局部结构有关。吸收峰位于6.3、5.8、5.2 eV处的CT带分别对应Yb-O-P、Yb-O-Si、Yb-O-Al连接。激发CT带导致Yb2+离子和氧空穴色心(OHC)产生,相应的化学方程式可以表示为: Yb^(3+)-O-R≡ ?〖 Yb〗^(2+)+ ■(°O-R≡@(R-OHC) ) (R=Al,Si,P) P/Al共掺比例对掺Yb3+石英玻璃的结构和辐射诱导色心有显著的影响。当P/Al<1时,Yb3+主要配位于[SiO4/2]0和[AlO4/2]-基团。Yb3+和[AlO4/2]-在辐射过程中分别俘获电子和空穴导致Yb2+和Al-OHC色心;当P/Al>1时,Yb3+主要配位于[O=P?O3/2]0(即P(3)基团)。P(3)基团的P=O双键在辐射过程中容易被电离破坏导致磷相关色心(P1,P2,P-OHC)形成。当P/Al=1时,Yb3+主要配位于[AlPO4]0基团。[AlPO4]0在辐射过程中不易得失电子。因此,铝和磷等掺在一定程度上可以提高掺Yb3+石英玻璃的抗辐射性能。 第四章系统研究了退火温度、退火气氛、氟含量对掺Yb3+石英玻璃结构、光谱性质和耐辐射性质的影响。研究表明平面三元环(D2)和平面四元环(D1)是形成Si-E′和NBOHC色心的前驱体,四配位铝(AlIV)是形成Al-OHC色心的前驱体。当Yb3+单掺石英玻璃结构弛豫到达平衡态时,玻璃的假想温度(Tf)等于退火温度。Tf越小,Yb3+单掺石英玻璃中D1和D2基团越少,抗辐射性能越好。氢气气氛下退火可以促进Yb3+/Al3+/Ce3+三掺石英玻璃发生结构弛豫,降低D1、D2和AlIV基团含量,增加低价态稀土离子(Ce3+、Yb2+)含量,显著提高玻璃的抗辐射性能。共掺氟也可以促进Yb3+/Al3+/Ce3+/F-四掺石英玻璃发生结构弛豫,降低D1、D2和AlIV基团含量,提高玻璃的抗辐射性能。 第五章研究了辐射条件、纤芯组分、预处理方法对掺Yb3+石英光纤耐辐射性质的影响。研究结果表明掺Yb3+石英光纤的辐射诱导损耗(RIA)对辐射总剂量和剂量率非常敏感,但对辐射源的类型(X或γ射线)不敏感。在相同辐射条件下,Yb3+/Al3+/F-共掺石英光纤的RIA值随着P5+和Ce3+的加入逐渐降低。载氢(H2)和载氘(D2)都可以显著提高掺Yb3+石英光纤的耐辐射性能,但缺点是H2或D2分子易扩散到光纤外,导致光纤的抗辐射性能失效。对MCVD法制备的预制棒在氘气气氛下热退火预处理,可以显著提高掺Yb3+石英光纤的抗辐射性能,且不会对辐射前光纤的损耗和激光斜率效率产生明显的负面影响。700 Gy伽马辐照后,该光纤的激光效率仅下降28%(72%→52%)。该光纤的抗辐射性能完全可以满足激光器在地球同步轨道上工作7年的总剂量要求(≤500 Gy)。 第六章是对全文工作的总结。指出本论文的创新点和不足之处,并给出后续研究建议。掺Yb3+石英玻璃,结构与缺陷,耐辐射光纤,光谱和激光性能,结构弛豫中国科学院上海光学精密机械研究所邵冲云材料学博士
中文题目: 掺Yb3+石英玻璃的结构、光谱与耐辐照性能及辐致暗化机理研究
外文题目: Study on structure, spectrum, radiation resistance and radiation-induced darkening mechanism of Yb3+-doped silica glasses
作者: 邵冲云
导师姓名: 胡丽丽
学位授予机构: 中国科学院上海光学精密机械研究所
答辩时间: 20190524
Yb3+-doped silica glass, structure and defects, radiation resistant optical fibers, spectrum and laser properties, structural relaxation
学位级别: 博士
正文语种: chi
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