Rare-earth-doped Fluoro-sulfo-phosphate-based High-gain Laser Glass And Fiber

High-performance fiber lasers（HP-FLs）,such as narrow-linewidth single-frequency FLs（SF-FLs）,and ultra-fast high-repetition-rate FLs（HRR-FLs）,are of pivotal importance across national security,scientific research,and industrial manufacturing.The high-gain active fiber fabricated by rare earth（RE）doped laser glass is the key medium and critical scientific problem of HP-FLs.However,commercial silica-based glass fibers exhibit a low RE solubility(～10¹⁹ions/cm³),resulting in a low gain coefficient,which hinders the development of HP-FLs.The mixed-anion fluoro-sulfo-phosphate（FSP）laser glasses are expected to provide high RE solubility(～10²¹ ions/cm³),large stimulated emission cross-section,and low nonlinear and dispersion coefficients,which are promising for high-gain fibers.However,few studies on the composition-structure-property（C-S-P）relationships,gain characteristics and lasing performance of FSP laser glasses and fibers are available.Herein,this thesis aims to enlarge the C-S-P databases of FSP glass as well as explore its potential for RE-doped high-gain laser glass and active fiber.The thesis consists of five chapters.The first chapter reviews the progress on phosphate,fluorophosphate,and FSP laser glasses and fibers along with their characteristics,progress,and existing problems,which is followed by the elaboration of current research goals and content.From the second chapter to the fifth chapter,systematic research is conducted in the perspectives of the glass-forming region（GFR）and C-S-P relations of FSP glass,spectroscopic characteristics of RE-doped FSP laser glass,design and fabrication of FSP-based gain fiber and the lasing performance characterization.The main results are as follows:（1）Six FSP glass systems with the compositions of AlF₃-R₂SO₄-RPO₃（R=Li,Na,K）and AlF₃-MSO₄-M（PO₃）₂（M=Ca,Sr,Ba）are designed.Their GFRs are quickly determined under the guidance of thermodynamic calculation and prediction,which can offer the compositional database for designing the matrix of FSP-based laser glasses and fibers.（2）The C-S-P relations of FSP glasses are studied and analyzed comprehensively.Further,we design a glass system with the compositions of AlF₃-Na₂SO₄-KPO₃-Zn（PO₃）₂（KZFSP）that has excellent anti-crystallization stability,mechanical property,and chemical durability,which is promising for high-gain laser glass and fiber.（3）The Judd-Ofelt theory is used to evaluate the spectroscopic properties of RE(Nd³⁺,Er³⁺/Yb³⁺)doped FSP laser glasses.High-efficient emission properties can be obtained from FSP laser glasses,which show a longer lifetime,a larger emission cross-section,and a larger figure of merit than those of some phosphate and fluorophosphate laser glasses.The FSP laser glasses are of great interest for preparing high-gain laser fibers.（4）Nd³⁺-doped（FSP-NDF）and Er³⁺/Yb³⁺-codoped（FSP-EYDF）FSP-based high-gain laser fibers are designed and fabricated.The homemade FSP-NDF and FSP-EYDF are used as gain media to demonstrate fiber lasers operating at～1.06μm and～1.5μm,respectively.The FSP-EYDF provides high net gain coefficients of 4.7 d B/cm@1535 nm and 0.6 d B/cm@1610nm,which are about 4 times higher than those of the silica-based fiber.A narrow-linewidth SF-FL（3.15 k Hz@1534.7 nm）and an ultra-fast HRR-FL（1.6 GHz@1610 nm）have been demonstrated by using the FSP-EYDF.These results indicate that RE-doped FSP-based high-gain fibers are promising for HP-FLs.