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Bell & Howell Information and Leaming 300 North Zeeb Road, Ann A-rbr, MI 48106-7346 USA EXPERIMENTAL STUDIES OF HARMONIC GENERATION FROM SOLID-DENSI'N PLASMAS PRODUCED BY PICBSECOND ULTRA-INTENSE LASER PULSES Liang Zhao A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Department of Physics University of Toronto O Copyright by Liang Zhao 1998 National Library Bibliothèque nationale 1+1 ,cm, du Canada Acquisitions and Acquisitions et Bibliographie Services services bibkographiques 395 Wellington Street 395. rue Wellington OttawaON KIAOM Ottawa ON KIA ON4 Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distnbute or sell reproduire, prêter, distribuer ou copies of this thesis in microfom, vendre des copies de cette thèse sous paper or electronic fonnats. la forme de microfiche/nlm, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur consewe la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor subsbntial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Experimental Studies of Harmonic Generation from Solid-Density Plasmas Produced by Picosecond Ultra-Intense Laser Pulses Doctor of Philosophy, 1998, Liang Zhao, Department of Physics, University of Toronto Abstract In this thesis, an experimental investigation of harmonic generation from high- intensity laser-plasma interactions is presented. Harmonic experiments performed on the 1-terawatt FCM-CPA laser system at the University of Toronto, and on the 10-terawatt T3 laser system at the University of Michigan, are described. Using the FCM-CPA laser, various aspects of second harmonic generation were investigated systematicaily, with a focus on the effect of preformed plasma on harmonic generation. Experiments comparing hamonics generated by high-contrast pulses and by pulses containing weak prepulses show that the preformed plasma causes spatial and spectral breakup of harmonics and diffuses harmonic emission into large solid angles. On the T3 laser system, mid-order harmonic generation from various solid materials was studied and both odd and even harmonics up to the 7th were observed. Important features of harmonic generation, Le., the laser-polarization dependence and the angular distribution of harmonic emission, were characterized. Purnp-probe expetiments were carried out as well on both laser systems by adding a controlled prepulse, which demonstrated a strong dependence of harmonic production efficiency on the gradient of preformed plasma. We also describe what we believe to be the first observation of regular satellite features accompanying the mid-order harmonics. Their dependence on target materials and on laser intensity was measured, and possible pbysical explanations are discussed. Besides, the development of the Toronto FCM-CPA laser system is summarized. Its original design and unique features are described in detail. Acknowledgments First, 1 would iike to thank my thesis supervisor, Professor Robin Marjoribanks, for his guidance and support during the course of this research. 1 thank him for introducing me to this fast developing, yet challenging research field and for providing me the opportunity of working in his lab. His advice and careful reading of various drafts of the manuscript have significantly improved the quality of this thesis. The members of rny Ph.D. supe~isorycommittee, Professor John Sipe and Professor Henry van Driel, have provided me a great amount of help in the past years. 1 am very grateful for the advice and assistance they have given to me. I would also like to thank Professor Paul Drake, Professor Aephrairn Steinberg, and Professor Peter Smith for their critical reading of my thesis and for their valuable suggestions. Constant help in many aspects provided by Mrs. Marianne IUiwana was also greatly appreciated. This work could not possibly have been completed without the support, help, and encouragement from my fellow graduate students, Fred Budnik and Gabor Kulcsh. During the past several years, it was their enthusiasm, Wendship, and optirnism that kept my spirit up, helped me to overcome the difficulties, and made this lab a much pleasant place to work and to study. 1 am also grateful to Professor Peter Heman, who kindly let me share most of his lab tools, and suggested many good ideas for my experiments. The assistance of other members in the group was also greatly appreciated. Among them are: Michel Stanier, James Mihaychuk, Hideo Yamakoshi, Sherry Crossly, Bin Xiao, Hiroyuki Higaki, Estelle Rouillon, and Adrian Vitcu. I would like to thank the Center for Ultrafast Optical Science at the University of Michigan for providing me the opportunity of working on their excellent facilities. In particular, 1 would like to thank Dr. Anatoly Maksimchuk and Robert Wagner for assisting the expeririients in many ways and for staying so many late nights running the laser system. Thanks also go to Dr. Jonathan Workman for providing his target materials to me, to Dr. Paul Le Blanc and Professor Michael Downer for allowing me to use their prepulse setup, and to Professor Donald Umstadter and Professor Gérard Mourou for their encouragement and generosity with laser time. My thanks aIso go to the staff in this department and at Photonic Research Ontario who constantly provided both excellent technicai support and necessary equipment whenever 1 needed either. Financial support frorn the University of Toronto Open Fellowship, from the Burton Scholarship at the Department of Physics, and from the research funding provided by the Natural Science and Engineering Research Council of Canada and Photonic Research Ontario, is also gratefully acknowledged. 1 am especially grateful to my parents. Through out these years, it was their continuing support and encouragement that motivated me working towards this final goal. Without their support I could not have reached this far. Lastly, and most importantly, 1 am deeply h debt to my wife, Yuanyuan, who endured ail the late nights and lost weekends with remarkable patience and understanding. Table of Contents Abstract Acknowledgments Table of Contents Chapter 1 Introduction 1.1 A Brief Historical Review of Harmonic Generation in Solids 1.2 Scope of this Thesis 1.3 Outline of the Dissertation 1.4 Role of the Author Chapter 2 Theoretid Background 2.1 Introduction to Laser-Plasma Interaction 2.1.1 Plasma Generated by Intense Laser Pulses on Solid Target 2.1.2 Waves in Plasma 2-1.3 Some Basic Processes in Laser-Plasma Interaction 2.2 Mechanisms of Harmonic Generation in an Overdense Laser- Produced Plasma Table of Contents Simple Hmonic-Generation Phenomenology Second Harmonic Generation: a Perturbation Theory Particle-in-Cell Simulation Results The Linear Mode-Coupling Model The Oscillating-~irrorModel Model Predictions: Harmonic Generation with Varying Experimental Parameters 2.3 RoIe of Preformed PIasma 2.3.1 Laser Prepulses 2.3.2 Effects of Preplasma on Harmonic Generation 2.3.3 Modification of Plasma Density Profde by a Deliberate Prepulse 2.4 Conclusions Chapter 3 Development of the Toronto FCM-CPA Laser System 3.1 Introduction to the CPA Technology 3.2 The Feedback-Controlled Mode-Locked (FCM) Oscillator 3.2.1 Purpose of Feedback Control in the Oscillator 3.2.2 Pulse Development in the FCM Oscillator 3.2.3 High-Contrast Characterization of Pulses from the FCM Osciliator 3 -3 The FCM-CPA Laser System 3.3.1 TheLaserSetup 3.3.2 Characterization of Beam Focus in the Target Chamber 3.3.3 Compressed Pulse Characterization Using High- Contrast Cross-cordation 3.3-4 Single-Shot Autocorrelation Table of Contents 3.4 A Novel Cross-correlation Technique 3 -4.1 Design of the WeiCross-correlator 3 -4.2 Experimental Results 3.5 Conclusions Chapter 4 Experimental Results of Second Harmonie Generation 4.1 Experimental Setup 4.2 Laser Pulse Cleaning with Saturable Absorber 4.3 Second Harmonic Generation (SHG) and the Effect of Prepulse