DEVELOPMENT OF A THULIUM GERMANATE THIN DISK LASER PROTOTYPE by Daniel Sickinger A Thesis Submitted to the Faculty of the COLLEGE OF OPTICAL SCIENCES In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE In the Graduate College THE UNIVERSITY OF ARIZONA 2016 STATEMENT BY AUTHOR The thesis titled Development of a Thulium Germanate Thin Disk Laser Prototype prepared by Daniel Sickinger has been submitted in partial fulfillment of requirements for a master’s degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that an accurate acknowledgement of the source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED: Daniel Sickinger APPROVAL BY THESIS DIRECTOR This thesis has been approved on the date shown below: Defense Date Xiushan Zhu 5/9/2016 Associate Research Professor of Optical Sciences Abstract A Thulium Germanate thin disk laser prototype is developed and its potential applications are discussed. Unfortunately, the thin disk gain material for the CW prototype was unable to lase due to thermal limitations within the disk. However, a CW output power model and a physical pump chamber module have been developed, along with the supporting Zemax models and alignment procedures so other gain materials and future improvements can be tested. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] i Acknowledgements I would like to take the time to first thank those who have helped me develop and understand lasers fundamentally, most notably, my advisor Xiushan Zhu and Valery Temyanko. Their ability to patiently answer my questions was invaluable to the experience I developed throughout this project. People to also thank are, Rolland Himmelhuber and Sasaan Showghi for opinions and ideas to point me in the right directions, as well as Todd Horne for the use of the machine shop and tools. Finally and most importantly, I would like to thank my parents, who I love dearly, for always being there for me under any experience I was facing in life. ii Contents Abstract ................................................................................................................... i Acknowledgements ............................................................................................... ii Contents ................................................................................................................ iii List of Figures ....................................................................................................... vi List of Tables ...................................................................................................... viii 1. Introduction ...................................................................................................... 1 1.1 History ...................................................................................................... 2 Rectangular Thin Slab Laser ................................................................... 2 Zig-Zag Thin Slab Laser .......................................................................... 3 Thin Disk Laser ........................................................................................ 4 1.2 Areas of Interest ....................................................................................... 7 Military Applications ............................................................................... 7 Medical Applications ............................................................................... 8 Material Processing ................................................................................. 8 Laser Sensing and Spectroscopy .............................................................. 9 1.3 Thulium Germanate Thin Disk as Potential ............................................. 9 Thulium Germanate as Gain Medium .................................................... 10 Thulium Germanate as a Thin Disk Laser ............................................. 11 1.4 Motivation and Intent ............................................................................. 12 2. Thin Disk Laser Basics .................................................................................. 13 2.1 Laser Gain Medium ................................................................................ 15 Amplifying Atoms ................................................................................... 15 Host Material ......................................................................................... 17 2.2 Laser Oscillator ...................................................................................... 18 iii Cavity Configurations ............................................................................ 18 Resonator Types ..................................................................................... 19 2.3 Pumping Configuration .......................................................................... 21 Pump Chamber ...................................................................................... 22 Source Optics ......................................................................................... 24 3. Laser Fundamentals and Modelling ............................................................ 25 3.1 Light Interactions ................................................................................... 25 Spontaneous Emission............................................................................ 27 Absorption .............................................................................................. 27 Stimulated Emission ............................................................................... 28 3.2 Laser Operation ...................................................................................... 28 Three Level System................................................................................. 29 Laser Assumptions ................................................................................. 31 3.3 Rate Equations........................................................................................ 33 Population Rate Equations .................................................................... 33 Photon Rate Equations........................................................................... 34 3.4 Gain Threshold ....................................................................................... 35 3.5 Pump Chamber Power Contribution ...................................................... 36 3.6 Resonator Effects ................................................................................... 39 Signal Aperture Effect ............................................................................ 39 Pump-Signal Coupling Value................................................................. 40 3.7 CW Power Output Model ....................................................................... 41 Output Power Equations ........................................................................ 41 Yb:YAG Thin Disk Laser Comparison ................................................... 42 4. Thin Disk Prototype Design .......................................................................... 45 4.1 Design Summary .................................................................................... 46 First Order Summary ............................................................................. 46 4.2 Component Selection and Manufacture ................................................. 47 Pump Source .......................................................................................... 47 Collimation Optics ................................................................................. 47 iv Parabolic Mirror.................................................................................... 48 Fold Mirrors .......................................................................................... 48 Thin Disk ................................................................................................ 49 Thin Disk Heatsink ................................................................................. 50 Resonator Configuration........................................................................ 51 Final System Layout ............................................................................... 52 4.3 Alignment and Assembly ....................................................................... 55 Thin Disk Reference Mirror to Parabolic Mirror .................................. 56 Four Fold Mirrors ................................................................................. 58 Pump Source and Collimation Optics .................................................... 60 Thin Disk and Resonator Optics ............................................................ 62 5. System Performance ...................................................................................... 63 5.1 Pump Spot Analysis ............................................................................... 63 Fiber Source ..........................................................................................