Clemson University TigerPrints All Dissertations Dissertations May 2020 The Materials Science and Engineering of Advanced YB-Doped Glasses and Fibers for High-Power Lasers Thomas Wade Hawkins Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_dissertations Recommended Citation Hawkins, Thomas Wade, "The Materials Science and Engineering of Advanced YB-Doped Glasses and Fibers for High-Power Lasers" (2020). All Dissertations. 2585. https://tigerprints.clemson.edu/all_dissertations/2585 This Dissertation is brought to you for free and open access by the Dissertations at TigerPrints. It has been accepted for inclusion in All Dissertations by an authorized administrator of TigerPrints. For more information, please contact [email protected]. THE MATERIALS SCIENCE AND ENGINEERING OF ADVANCED YB-DOPED GLASSES AND FIBERS FOR HIGH-POWER LASERS A Dissertation Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Materials Science and Engineering by Thomas Wade Hawkins May 2020 Accepted by: Dr. Liang Dong, Committee Chair Dr. John Ballato Dr. Peter Dragic Dr. Stephen Foulger Dr. Philip Brown ABSTRACT This research studies and yields new understandings into the materials science and engineering of advanced multicomponent glass systems, which is critical for next generation fiber lasers operating at high output powers. This begins with the study and development of Yb-doped glasses in the Al2O3-P2O5-SiO2 (APS) ternary system, fabricated using modified chemical vapor deposition (MCVD), that, despite being highly doped, possess an average refractive index matched to that of silica (SiO2). The highly doped active core material was subsequently processed through a multiple stack-and- draw process to realize a single fiber with high doping, compositionally-tailored index, and scalability for fiber lasers. Based on the knowledge gained in this first focal area, further strategic compositional tailoring to influence the glass’ photoelastic and thermo- optic coefficient, was performed in order to understand and realize significant decreases in Brillouin and thermal-Rayleigh scattering, which instigate parasitic stimulated Brillouin scattering (SBS) and transverse mode instabilities (TMI) in high power fiber lasers. In addition to understanding the composition / structure / properties of these glasses, a double-clad fiber laser will be fabricated, scaled to over 1 kW of output laser power, and studied in order to relate the materials science and engineering of multiple glass systems and fibers designs to laser performance and properties. ii DEDICATION This dissertation is dedicated to my wife Wendy and my son Wade. They are the foundation of solid support along this journey. Without her ability to encourage me to change perspectives when needed, refocus, and just sometimes stop to assess how fortunate I am, there is almost no chance this dissertation would have been written. This really is for the two of you, and I could not have finished this without the two of you in my life. iii ACKNOWLEDGMENTS I would like to acknowledge and give thanks to my advisor, Dr. Liang Dong on this research. He afforded me the opportunity to vary my research paths and focus on materials aspects of fiber laser research. More importantly, he encouraged me to engage further into the research that more clearly aligned with my focus and goals for deeper understanding as they reflect the materials. I would also like to thank Dr. John Ballato for his guidance and mentorship on the writing process to create a compelling story with my research, as well as one that meets both the goals of a PhD in Materials Science and Engineering, but also one that aligns with our optical fiber understanding and fabrication strengths in the labs. I’d like to thank my committee members, Dr. Peter Dragic, Dr. Stephen Foulger, and Dr. Phil Brown, for their time supporting and feedback on my research. I want to thank both present and past group members that have been around through the course of my work on this dissertation. Pretty much all of you have already graduated and moved on to your own professional careers, but I thank you for your guidance and support on this work, even if it was just confidence that I would get it done. Finally I would like to thank and acknowledge the Army Research Lab and Joint Technology Office for their financial support for this research. iv TABLE OF CONTENTS Page TITLE PAGE .................................................................................................................... i ABSTRACT ..................................................................................................................... ii DEDICATION ................................................................................................................ iii ACKNOWLEDGMENTS .............................................................................................. iv LIST OF TABLES ........................................................................................................ viii LIST OF FIGURES ........................................................................................................ ix CHAPTER I. HIGH-POWER FIBER LASERS: BACKGROUND, RARE EARTH PROPERTIES, AND OPTICAL NONLINEARITIES ................................ 1 1.1 Brief history of Optical Fibers .......................................................... 1 1.2 Optical Fiber Fabrication ................................................................... 2 1.3 Fiber Lasers ....................................................................................... 7 1.4 Rare Earths for Fiber Lasers .............................................................. 8 1.4.1 Ytterbium Fiber Lasers .............................................................. 8 1.4.2 Erbium Fiber Lasers ................................................................. 10 1.4.3 Thulium and Holmium Fiber Lasers ........................................ 13 1.5 Optical Nonlinearities ..................................................................... 16 1.5.1 Stimulated Brillouin Scattering (SBS) ..................................... 16 1.5.2 Transverse Mode Instability (TMI) ......................................... 20 1.5.3 Photodarkening ........................................................................ 22 1.6 Purpose of this Dissertation ............................................................. 23 1.7 References ........................................................................................ 26 II. EXPERIMENTAL ....................................................................................... 36 2.1 Introduction ...................................................................................... 36 2.2 MCVD preform fabrication ............................................................ 36 2.3 MCVD preform fabrication at Clemson ......................................... 40 2.4 Preform Characterization ................................................................. 48 2.5 Preform preparation – grinding and polishing ................................. 52 v Table of Contents (Continued) Page 2.6 Active glass stack orientation .......................................................... 54 2.7 Stacking and glass-working ............................................................. 56 2.8 Active Cane Draw ............................................................................ 59 2.9 Active Glass Redraw ........................................................................ 61 2.10 Integration and fiber fabrication .................................................... 63 2.11 Stacking, tacking, and over-clad .................................................... 64 2.12 Stack to Cane Draw ....................................................................... 67 2.13 Cane to Fiber draw ......................................................................... 70 2.14 References ...................................................................................... 73 III. STUDY AND DEVELOPMENT OF ACTIVE LASER GLASS ............... 76 3.1 Introduction and Research Motivation............................................. 76 3.2 Creation of a Phosphosilicate Glass ................................................. 78 3.3 Al2O3 doping for enhanced RE solubility in SiO2 ........................... 82 3.4 Tailoring refractive index materially ............................................... 83 3.5 Active Aluminophosphosilicate glass with Ytterbium .................... 84 3.6 Active Core Glass Creation ............................................................. 86 3.7 Active core integration into fiber ..................................................... 95 3.8 Active Core Glass Reevaluation and Revision .............................. 106 3.9 Summary, Conclusions and Future Work ...................................... 116 3.10 References .................................................................................... 120 IV. LOW THERMO-OPTIC COEFFICIENT FIBER ..................................... 128 4.1 Introduction and Background ........................................................ 128 4.2 Thermally-driven Optical Nonlinearities ....................................... 128 4.3 Low Thermo-optic Coefficient Preform and Fiber Fabrication ....................................................................... 131 4.4 Material Additivity Modeling .......................................................