Air Force Institute of Technology AFIT Scholar Theses and Dissertations Student Graduate Works 3-23-2018 Two-Photon Excitation of Cesium Alkali Metal Vapor 72D, 82D Kinetics and Spectroscopy Ricardo C. Davila Follow this and additional works at: https://scholar.afit.edu/etd Part of the Engineering Physics Commons Recommended Citation Davila, Ricardo C., "Two-Photon Excitation of Cesium Alkali Metal Vapor 72D, 82D Kinetics and Spectroscopy" (2018). Theses and Dissertations. 1744. https://scholar.afit.edu/etd/1744 This Dissertation is brought to you for free and open access by the Student Graduate Works at AFIT Scholar. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of AFIT Scholar. For more information, please contact [email protected]. TWO-PHOTON EXCITATION OF CESIUM ALKALI METAL VAPOR 72D, 82D KINETICS AND SPECTROSCOPY DISSERTATION Ricardo C. Davila, Civilian, USAF AFIT-ENP-DS-18-M-076 DEPARTMENT OF THE AIR FORCE AIR UNIVERSITY AIR FORCE INSTITUTE OF TECHNOLOGY Wright-Patterson Air Force Base, Ohio DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED The views expressed in this dissertation are those of the author and do not reflect the official policy or position of the United States Air Force, the Department of Defense, or the United States Government. This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. AFIT-ENP-DS-18-M-076 TWO-PHOTON EXCITATION OF CESIUM ALKALI METAL VAPOR 72D, 82D KINETICS AND SPECTROSCOPY DISSERTATION Presented to the Faculty Graduate School of Engineering and Management Air Force Institute of Technology Air University Air Education and Training Command in Partial Fulfillment of the Requirements for the Degree of Doctorate of Philosophy in Engineering Physics Ricardo C. Davila, M.S. Civilian, USAF March 2018 DISTRIBUTION STATEMENT A: APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED AFIT-ENP-DS-18-M-076 TWO-PHOTON EXCITATION OF CESIUM ALKALI METAL VAPOR 72D, 82D KINETICS AND SPECTROSCOPY Ricardo C. Davila, M.S. Civilian, USAF Committee Membership: Glen P. Perram, PhD Chairman Kevin C. Gross, PhD Member Mark E. Oxley, PhD Member ADEDJI B. BADIRU, PhD Dean, Graduate School of Engineering and Management AFIT-ENP-DS-18-M-076 Abstract 2 2 Pulsed excitation on the two-photon Cs 6 S 1=2 −! 7 D3=2;5=2 transition results in time-resolved fluorescence at 697 nm and 672 nm. The rates for fine structure mixing 2 between the 7 D3=2;5=2 states have been measured for helium and argon rare gas collision partners. The mixing rates are very fast, 1:26 ± 0:05 × 10−9 cm3=(atom sec) for He and 1:52 ± 0:05 × 10−10 cm3=(atom sec) for Ar, driven by the small energy splitting and large radial distribution for the valence electron. The quenching rates are considerably slower, 6:84 ± 0:09 × 10−11 cm3=(atom sec) and 2:65 ± 0:04 × 10−11 cm3=(atom sec) for He and Ar, respectively. The current results are placed in context with similar rates for other alkali-rare gas collision pairs using adiabaticity arguments. 2 2 Pulsed excitation on the two-photon Cs 6 S 1=2 −! 8 D3=2; 5=2 transition results in time- 2 resolved fluorescence at 601 nm. The rates for fine structure mixing between the 8 D3=2; 5=2 states have been measured for helium and argon rare gas collision partners. The mixing rates are very fast, 2:6 ± 0:2 × 10−9 cm3=(atom s) for He and 5:2 ± 0:4 × 10−10 cm3=(atom s) 2 2 for Ar, about 2-3 times faster than for the Cs 7 D5=2 7 D3=2 relaxation. The quenching rates are also rapid, 1:07 ± 0:04 × 10−10 cm3=(atom s) and 9:5 ± 0:7 × 10−11 cm3=(atom s) for He and Ar, respectively. The rapid fine structure rates are explained by the highly impulsive nature of the collisions and the large average distance of the valence electron from the nucleus. Quenching rates (inter-multiplet transfer) are likely enhanced by the closely spaced, 9 2P levels. Stimulated emission on the ultraviolet and blue transitions in Cs has been achieved 2 2 by pumping via two-photon absorption for the pump transition 6 S 1=2 ! 7 D5=2;3=2. The performance of the optically-pumped cesium vapor laser operating in ultraviolet and blue has been extended to 650 nJ/pulse for 387 nm, 1:3 µJ/pulse for 388 nm, 200 nJ/pulse for 455 nm and 500 nJ/pulse for 459 nm. Emission performance improves dramatically as the iv cesium vapor density is increased and no scaling limitations associated with energy pooling or ionization kinetics have been observed. v Acknowledgments First, I would like to thank my wife and daughter for putting up with me during the many hours I spent on course work, research and work demands. Balancing work and family time is not my forte; but, it’s my family’s support and encouragement that keeps me going each day. Second, my mother, father and brother are role models – I can’t thank them enough for the parts they played in my upbringing and encouragement they continue to provide today. Third, I received assistance and friendship from the AFIT laser research team (Capt Wooddy Miller, Ben Eshel, Capt Nate Haluska, Capt. AJ Wallerstein, and Capt Bill Bauer) and my AFRL leadership and co-workers. Many thanks to AFIT ENP’s lab techs, Greg Smith and Mike Ranft, for all their support and special kudos to Chris Rice and Aaron Archibald, whose assistance in my experimental configurations was critical. It was Aaron’s optical bench setup that allowed me to work my two spin-orbit rate experiments. Fourth, I appreciate the help I received from my committee members. Dr Kevin Gross and Dr Mark Oxley were my professors for quantum physics, spectroscopy and mathematics. I enjoyed your courses and your teaching styles. Thank you for giving me a deeper appreciation of physics and math. Finally, I would like to thank Dr. Glen Perram. I can’t thank you enough for your patience, mentorship and advisement. I’m glad our paths continue to cross in my current AFRL work. Ricardo C. Davila vi Table of Contents Page Abstract......................................... iv Acknowledgments.................................... vi Table of Contents.................................... vii List of Figures...................................... ix List of Tables...................................... xi List of Symbols..................................... xii I. Introduction.....................................1 II. Background and Literature Review.........................5 2.1 Diode Pumped Alkali Laser (DPAL).....................5 2.2 Alkalis.....................................7 2.3 DPAL Spin-orbit Rate Kinetics........................ 13 2.3.1 Pulsed Experiment.......................... 14 2.3.2 Adiabaticity Theory......................... 16 2.4 Cs UV and blue laser emission study..................... 19 III. Spin-orbit Relaxation of Cesium 72D in Mixtures of Helium and Argon..... 22 3.1 Introduction.................................. 22 3.2 Kinetic Analysis................................ 24 3.3 Experiment.................................. 27 3.4 Results..................................... 29 3.5 Discussion................................... 34 3.6 Conclusions.................................. 34 IV. Time Resolved Fine Structure Mixing of Cesium 8 2D Induced by Helium and Argon........................................ 35 4.1 Introduction.................................. 35 4.2 Methods.................................... 37 4.3 Results..................................... 38 vii Page 4.4 Discussion................................... 42 4.5 Conclusions.................................. 49 V. Ultraviolet and Blue Stimulated Emission from Cs Alkali Vapor Pumped using Two-Photon Absorption............................... 52 5.1 Introduction.................................. 52 5.2 Experiment.................................. 55 5.3 Results..................................... 59 5.4 Discussion................................... 68 5.5 Conclusions.................................. 82 VI. Conclusions..................................... 83 6.1 Work Summary................................ 83 6.2 DPAL Impact................................. 84 6.3 Recommendation for future work....................... 85 6.3.1 Deleterious Processes in the Cesium DPAL Cell........... 85 6.3.2 Full kinetic theory model to explain UV and blue laser emissions. 86 Appendix: Electric Dipole Line Strength Calculation................. 88 Bibliography...................................... 91 viii List of Figures Figure Page 2.1 DPAL energy levels................................6 2.2 Combined Cs number density as a function of temperature........... 10 2.3 Alkali energy levels for n2D fine structure collisional mixing.......... 13 2.4 Alkali probabilities versus adiabaticity...................... 19 3.1 Cs energy level diagram.............................. 23 3.2 Cs fine structure collisional mixing........................ 24 3.3 SO experiment setup............................... 27 3.4 Cs 72D laser excitation spectra.......................... 30 3.5 Cs emission intensity............................... 30 2 2 3.6 Fluorescence decay curves of the Cs 7 D3=2 −! 6 P1=2 emission......... 31 2 2 3.7 Emission on Cs 7 D5=2 −! 6 P3=2 ......................... 32 3.8 Stern-Volmer plot of experimentally derived rates................ 32 3.9 Log probabilities are plotted against the calculated adiabaticities........ 33 4.1 Equipment apparatus and cesium energy levels................. 38 4.2 Fluorescence decay curves............................ 39 2 2 2 4.3 Emission on 8 D3=2 −! 6 P1=2 at 601 nm after