GENERATION OF RADIO FREQUENCY INDUCED METASTABLE XENON AS A GAIN MEDIUM FOR DIODE PUMPED RARE GAS LASER SYSTEMS by JACQUELINE MARIE ANDREOZZI A THESIS Submitted in partial fulfillment of the requirements for the degree of Master of Science in The Department of Electrical Engineering to The School of Graduate Studies of The University of Alabama in Huntsville HUNTSVILLE, ALABAMA 2013 ACKNOWLEDGMENTS The research presented in this thesis would not have been possible without the substantial guidance, effort and assistance of several people. I would first like to thank my adviser, Dr. John Williams, for his willingness and enthusiasm to take on this project. His expertise and knowledge were undoubtedly a major factor in the success of the project. I would also like to thank the members of my committee, Dr. Richard Fork and Dr. Lingze Duan, for their respected input and advice regarding this research. I would also like to thank Mrs. Amanda Clark, Dr. Greg Finney and Mr. Keff Edwards for their continuous support and intellectual contributions as the project progressed. The experience and ideas of these three individuals largely impacted the final experimental design, and proved invaluable for the success of the research. Finally, it is essential that I acknowledge the generous funding given to this project by the U.S. Army Space and Missile Defense Command. The assistance and technical advice of Dr. Kip Kendrick and Mr. Adam Aberle at this organization was crucial to the success of this research. v TABLE OF CONTENTS Page LIST OF FIGURES ………………………………………………………………………………………....…………….……….……. ix LIST OF TABLES …………………………………………………………………………………………………………..……….…… xii Chapter 1 INTRODUCTION TO GAS LASER SYSTEMS .................................................................................. 1 1.1: Interest in High Energy Lasers ............................................................................................ 3 1.2: The Evolution of Legacy Systems ........................................................................................ 5 1.3: Diode Pumped Alkali Lasers................................................................................................ 8 1.4: Diode Pumped Rare Gas Lasers ........................................................................................ 15 2 REVIEW OF THE LITERATURE ................................................................................................... 20 2.1: Atomic Properties of Interest and Notation ..................................................................... 21 2.1.1: Absorption and Fluorescence ....................................................................................... 26 2.1.2 Atomic Laser Model ...................................................................................................... 31 2.1.3: Lifetimes ....................................................................................................................... 36 2.1.4: Efficiencies .................................................................................................................... 38 2.2: Alkali Atoms ...................................................................................................................... 42 2.3: Cesium .............................................................................................................................. 44 2.4: Rare Gas Atoms ................................................................................................................ 49 vi 2.5: Xenon ................................................................................................................................ 51 2.5.1: Hyperfine Structure of the Xenon Transition .............................. 59 2.5.2: Hyperfine Structure of the Xenon Transition .............................. 66 2.7: Optical Pumping ............................................................................................................... 72 2.8: Previous Studies ................................................................................................................ 77 3 CESIUM EXPERIMENT AND CALIBRATION ............................................................................... 80 3.1: Experiment Equipment and Setup .................................................................................... 80 3.1.1: Tunable Diode Laser ..................................................................................................... 83 3.1.2: Absorption Detector ..................................................................................................... 83 3.1.3: Fabry-Perot Interferometer .......................................................................................... 84 3.1.4: Cesium Reference Cell .................................................................................................. 87 3.2: Experiment Results and Data Analysis ............................................................................. 87 3.2.1: Temperature Dependence of Absorption Strength ...................................................... 89 3.2.2: Hyperfine Splitting of the Cesium D1 Line .................................................................... 92 4 DESIGN OF XENON EXPERIMENT........................................................................................... 101 4.1: Gas Flow and Pressure Control ....................................................................................... 102 4.2: Rare Gas Test Cell ........................................................................................................... 107 4.3: Radio Frequency Capacitive Discharge ........................................................................... 113 4.4: Tunable Diode Laser and Optics ..................................................................................... 115 4.5: Computer Interface ........................................................................................................ 117 vii 5 ABSORPTION MEASUREMENTS AND CALCULATIONS ........................................................... 119 5.1: First Glow of Xenon and Plasma Characterization ......................................................... 121 5.2: Absorption Spectra of Metastable Xenon Cell ................................................................ 128 5.3: Xenon Absorption Profile Analysis .................................................................................. 134 5.3.1: The Measured Absorption Profile of the Xenon Transition ...... 135 5.3.2: The Measured Absorption Profile of the Xenon Transition ...... 140 5.4: Principles that Affect the Observed Absorption Profiles and Causes of Error ................ 145 5.4.1: Natural Linewidth Broadening ................................................................................... 145 5.4.2: Pressure Broadening .................................................................................................. 147 5.4.3: Doppler Broadening ................................................................................................... 149 5.4.4: Isotope Broadening .................................................................................................... 152 6 CONCLUSIONS AND FUTURE RESEARCH ............................................................................... 156 6.1: Experiment Conclusions .................................................................................................. 156 6.2: Future Research .............................................................................................................. 159 6.2.1: Measurements at Atmospheric Pressure ................................................................... 160 6.2.2: Comparison to Cesium DPAL Cell ............................................................................... 160 6.3.3: Rare Gas Laser Cavity ................................................................................................. 161 7 REFERENCES .......................................................................................................................... 162 viii LIST OF FIGURES Figure Page 1.1: Theoretical lasing process of Diode Pumped Rare Gas Lasers (DPRGLs). ............................ 16 2.1: Simplified illustration of the electron configuration of xenon, organized into each n level. By formula: .............................................. 23 2.2: An illustration of how gain is achieved through population inversion. ............................... 32 2.3: A general phase diagram illustrating the difference between a vapor and a gas. .............. 43 2.4: Simplified electron configuration illustration of cesium. ..................................................... 44 2.5: Hyperfine splitting of the energy levels of cesium (not drawn to scale). Frequency values taken from Steck. [28].................................................................................................................... 47 2.6: Hyperfine structure of 129Xe around the 904.8 nm absorption line. .................................... 62 2.7: Hyperfine structure of 131Xe around the 904.8 nm absorption line. .................................... 65 2.8: Hyperfine structure of 129Xe around the 882.2 nm absorption line. .................................... 69 2.9: Hyperfine structure of 131Xe around the 882.2 nm absorption line. .................................... 71 2.10: General three-level atomic laser scheme, using indirect pumping. .................................... 73 2.11: A possible pump and lasing scheme