Understanding Lasers: An Entry Level Guide, 3rd Edition by Jeff Hecht

4858a28e728353f-261x361.jpeg Author Jeff Hecht
Isbn 9780470088906
File size 37MB
Year 2008
Pages 496
Language English
File format PDF
Category physics


IEEE PRESS Understanding Science & Technology Series The IEEE PRESS Understanding Series treats important topics in science and technology in a simple and easy-to-understand manner. Designed expressly for the nonspecialist engineer, scientist, or technician as well as the technologically curious— each volume stresses practical information over mathematical theorems and complicated derivations. Other books in the series include: Understanding the Nervous System An Engineering Perspective by Sid Deutsch, Visiting Professor, University of South Florida, Tampa Alice Deutsch, President, Bioscreen, Inc., New York 1993 Softcover 408 pp ISBN 0-87942-296-3 Understanding Telecommunications and Lightwave Systems An Entry-Level Guide by John G. Nellist, Consultants, Sarita Enterprises Ltd. 1992 Softcover 200 pp ISBN 0-7803-0418-7 Tele-Visionaries: The People Behind the Invention of Television by Richard C. Webb 2005 184pp ISBN 978-0471-71156 . UNDERSTANDING LASERS An Entry-Level Guide Third Edition JEFF HECHT IEEE Press Understanding Science & Technology Series IEEE Lasers and Electro-Optics Society, Sponsor ♦IEEE IEEE Press WILEY A JOHN WILEY & SONS, INC., PUBLICATION IEEE Press 445 Hoes Lane Piscataway, NJ 08855 IEEE Press Editorial Board Lajos Hanzo, Editor in Chief R. Abari J. Anderson S. Basu A. Chatterjee T. Chen T. G. Croda S. Farshchi B. M. Hammerli O. Malik S. Nahavandi M. S. Newman W. Reeve Kenneth Moore, Director of IEEE Book and Information Services (BIS) Steve Welch, IEEE Press Manager Jeanne Audino, Project Editor Technical Reviewers Jens Buus, Gayton Photonics Ltd., UK Kent Choquette, University of Illinois at Urbana-Champaign IEEE LEOS, Sponsor IEEE LEOS Liaison to IEEE Press, Carmen Menoni Copyright © 2008 by the Institute of Electrical and Electronics Engineers, Inc. All rights reserved. Published by John Wiley & Sons, Inc., Hoboken, New Jersey Published simultaneously in Canada. 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Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representation or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information on our other products and services please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print, however, may not be available in electronic formats. For more information about Wiley products, visit our web site at www.wiley.com. Library of Congress Cataloging-in-Publication Data is available. ISBN 978-0470-08890-6 Printed in the United States of America. 10 9 8 7 6 5 4 3 2 1 To the memory of family, friends, and members of the laser community who have passed away since the last edition: My parents, George T. and Laura Hecht; Howard Rausch, who taught me how to write about lasers; laser pioneers Theodore Maiman, Gordon Gould, and Arthur Schawlow; and my friend and editor Heather Messenger. CONTENTS Preface CHAPTER 1 xi Introduction and Overview 1.1 1.2 1.3 1.4 1.5 1.6 CHAPTER CHAPTER CHAPTER 2 3 4 The Idea of the Laser What is a Laser? Laser Materials and Types Optical Properties of Laser Light How Lasers are Used What Have We Learned? 1 3 7 10 15 17 Physical Basics 21 2.1 2.2 2.3 2.4 2.5 21 29 41 49 55 Electromagnetic Waves and Photons Quantum and Classical Physics Interactions of Light and Matter Basic Optics and Simple Lenses What Have We Learned? How Lasers Work 59 3.1 3.2 3.3 3.4 3.5 3.6 3.7 59 60 66 73 81 84 88 Building a Laser Producing a Population Inversion Resonant Cavities Laser Beams and Resonance Wavelength Selection and Tuning Laser Excitation Techniques What Have We Learned? Laser Characteristics 93 4.1 4.2 4.3 93 Coherence Laser Wavelengths Behavior of Laser Beams 96 101 vii VÜi CONTENTS 4.4 4.5 4.6 4.7 4.8 CHAPTER 5 Optics and Laser Accessories 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 CHAPTER 6 7 7.10 8 Laser Oscillators and Optical Amplifiers Laser Media The Importance of Gain Broadband and Wavelength-Tunable Lasers Laser-Like Light Sources What Have We Learned? Gas Lasers 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 CHAPTER Classical Optical Devices Transparent Optical Materials Optical Surfaces, Coatings and Filters Nonlinear Optics Beam Intensity and Pulse Control Beam Direction and Propagation Mounting and Positioning Equipment Optical Measurement What Have We Learned? Types of Lasers 6.1 6.2 6.3 6.4 6.5 6.6 CHAPTER Laser Power Laser Efficiency Duration of Emission Polarization What Have We Learned? The Gas Laser Family Gas-Laser Basics Helium-Neon Lasers Argon- and Krypton-Ion Lasers Metal-Vapor Lasers Carbon Dioxide Laser Excimer Lasers Chemical Lasers Other Gas Lasers What Have We Learned? Solid-State and Fiber Lasers 8.1 8.2 8.3 8.4 8.5 What is a Solid-State Laser? Solid-State Laser Materials Optical Pumping Ruby Lasers Neodymium Lasers 105 108 113 117 119 125 125 136 137 141 145 151 153 155 157 161 161 166 173 175 178 180 185 185 186 193 197 200 203 208 212 215 216 223 223 225 230 234 237 CONTENTS 8.6 8.7 8.8 8.9 8.10 8.11 CHAPTER 9 CHAPTER IO CHAPTER 11 Vibronic and Tunable Solid-State Lasers Erbium and Other Eye-Safe Lasers Rare-Earth-Doped Fiber Lasers Rare-Earth-Doped Fiber Amplifiers Raman Fiber Lasers and Amplifiers What Have We Learned? IX 243 249 250 256 258 259 Semiconductor Diode Lasers 265 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10 9.11 9.12 9.13 9.14 265 267 276 281 286 290 294 297 298 300 302 308 309 312 Basics of Semiconductor Diode Lasers Semiconductor Basics Light Emission at Junctions Layers and Confinement in Diode Lasers Confinement in the Junction Plane Edge-Emitting Diode Lasers Surface-Emitting Diode Lasers Quantum Wells and Dots Quantum Cascade Lasers Optical Properties of Diode Lasers Diode Laser Materials and Wavelengths Silicon Lasers Packaging and Specialization of Diode Lasers What Have We Learned? Other Lasers and Related Sources 317 10.1 10.2 10.3 10.4 10.5 317 323 328 332 334 Tunable Dye Lasers Extreme-Ultraviolet Sources Free-Electron Lasers Silicon Lasers What Have We Learned? Low-Power Laser Applications 339 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9 11.10 11.11 11.12 340 341 344 347 350 355 359 361 363 369 372 372 Advantages of Laser Light Reading with Lasers Optical Disks and Data Storage Laser Printing and Marking Fiber-Optic Communications Laser Measurement Laser Pointers, Art, and Entertainment Low-Power Defense Applications Sensing and Spectroscopy Holography Other Low-Power Applications What Have We Learned? X CONTENTS CHAPTER 12 High-Power Laser Applications 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 12.10 12.11 CHAPTER 13 High-Versus Low-Power Laser Applications Attractions of High-Power Lasers Materials Working Electronics Manufacturing Three-Dimensional Modeling Laser Medical Treatment Photochemistry and Isotope Separation Laser-Driven Nuclear Fusion High-Energy Laser Weapons Futuristic High-Power Laser Ideas What Have We Learned? 377 377 378 379 387 389 390 398 401 403 409 410 Lasers In Research 415 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.10 13.11 415 417 421 423 424 425 426 428 430 430 433 Lasers Open New Opportunities Laser Spectroscopy Manipulating Tiny Objects Atom Lasers and Bose-Einstein Condensates Slow Light Nanoscale Lasers Petawatt Lasers Attosecond Pulses Laser Acceleration Other Emerging Research What We Have Learned Answers to Quiz Questions 437 Appendix A: Laser Safety 441 Appendix B: Handy Numbers and Formulas 447 Appendix C: Resources and Suggested Readings 451 Glossary 455 Index 467 PREFACE "For Credible Lasers, See Inside. " I HE LASER is LESS THAN three years younger than the space age. Just days after the Soviet Union launched Sputnik I on October 4, 1957, Charles Townes and Gordon Gould had two crucial discussions at Columbia University about the idea that would become the laser. As the United States and Soviets launched the space race, Townes and Gould went their separate ways and started their own race to make the laser. On May 16, 1960, Theodore Maiman crossed the laser finish line, demonstrating the world's first laser at Hughes Research Laboratories in California. Bright, coherent, and tightly focused, laser beams were a new kind of light that excited the imagination. Science fiction writers turned their fictional ray guns into lasers with a stroke of the pen. Science writers inhaled deeply of the technological optimism of the early 1960s and wrote breathless predictions about the future of "the incredible laser." An article in the November 11,1962 issue of the Sunday newspaper supplement This Week revealed U.S. Army schemes for equipping soldiers with a "death-ray gun . . . small enough to be carried or worn as a side-arm." It quoted Air Force Chief of Staff Curtis E. LeMay predicting that ground-based lasers could zap incoming missiles at the speed of light. The reality was something else. A bemused Arthur Schawlow, who had worked with Townes on the laser, posted a copy of "The Incredible Laser" on his door at Stanford University, along with a note that read, "For credible lasers, see inside." Irnee D'Haenens, who had helped Maiman make the first laser, called the laser "a solution looking for a problem," a joke that summed xi XU PREFACE up the real situation. The infant laser had tremendous potential, but it had to grow up first. D'Haenens's joke lasted many years. So did the popular misconception that lasers were science-fictional weapons. If you told your neighbors you worked with lasers in the 1970s, they inevitably thought you were building death rays. That began to change as supermarkets installed laser scanners to automate checkout in the early 1980s. Then lasers began playing music on Compact Discs. Laser printers, laser pointers, CD-ROMs, and DVD players followed. Laser surgery became common, particularly to treat eye disease. Surveyors, farmers, and construction workers used lasers to draw straight lines in their work. Lasers marked serial numbers on products, drilled holes in baby-bottle nipples, and did a thousand obscure tasks in industry. Lasers transmitted billions of bits per second through optical fibers, becoming the backbone of the global telecommunications network and the Internet. The incredible laser has become credible, a global business with annual sales in the billions of dollars. Lasers have spread throughout science, medicine and industry. Lasers are essential components in home electronics, buried inside today's CD and DVD players, and vital to tomorrow's high-definition disk systems. It's a rare household that doesn't own at least one laser. Yet lasers have not become merely routine; they still play vital roles in Nobel-grade scientific research. This book will tell you about these real-world lasers. To borrow Schawlow's line, "For credible lasers, see inside." It will tell you how lasers work, what they do, and how they are used. It is arranged somewhat like a textbook, but you can read it on your own to learn about the field Each chapter starts by saying what it will cover, ends by reviewing key points, and is followed by a short multiple-choice quiz. We start with a broad overview of lasers. The second chapter reviews key concepts of physics and optics that are essential to understand lasers. You should review this even if you have a background in physics, especially to check basic optical concepts and terms. The third and fourth chapters describe what makes a laser work and how lasers operate. The fifth chapter describes the optical accessories used with lasers. Try to master each of these chapters before going on to the next. The sixth through tenth chapters describe various types of lasers. Chapter 6 gives an overview of laser types and configura- PREFACE XÜi tions, and explains such critical concepts as the difference between laser oscillation and amplification, the importance of laser gain, and tunable lasers. Chapter 7 describes the workings of gas lasers and important types such as the helium-neon and carbondioxide lasers. Chapter 8 covers solid-state and fiber lasers, including neodymium lasers and fiber lasers and amplifiers. Chapter 9 covers the hot area of semiconductor diode lasers, including the important new blue diode lasers. Chapter 10 describes other types of lasers, including tunable dye lasers, extreme ultraviolet sources, free-electron lasers, and efforts to develop silicon lasers. The final three chapters cover laser applications, divided into three groups. Chapter 11 describes low-power applications, including communications, measurement, and optical data storage. Chapter 12 covers high-power applications, including surgery, industrial materials processing, and laser weapons. Chapter 13 focuses on research and emerging developments in areas including spectroscopy, slow light, laser cooling, and extremely precise measurements. The appendices, glossary, and index are included to help make this book a useful reference. To keep this book to a reasonable length, we concentrate on lasers and their workings. We cover optics and laser applications only in brief, but after reading this book you may want to study them in more detail. I met my first laser in college and have been writing about laser technology since 1974.1 have found it fascinating, and I hope you will, too. JEFF HECHT Auburndale, Massachusetts January 2008 CHAPTER / INTRODUCTION AND OVERVIEW ABOUT THIS CHAPTER This chapter will introduce you to lasers. It will give you a basic idea of their use, their operation, and their important properties. This basic understanding will serve as a foundation for the more detailed descriptions of lasers and their operation in later chapters. 1.1 THE IDEA OF THE LASER Optics was a sleepy backwater of physics when Theodore Maiman demonstrated the first laser in 1960. His announcement made headlines, and for many years afterward, lasers were novelties that attracted attention. Today, lasers are commonplace in developed countries. Thanks in large part to the laser, optics has become a dynamic field, expanding far beyond the binoculars, cameras, and spectacles that were the main products of the optical industry half a century ago. We take lasers almost for granted today, as just another wonder of our technological age along with satellites and electronic chips. Most of us think of lasers as cylindrical devices that emit pencil-thin beams of red or green light, and shine bright spots on the wall. The first kind of laser to come to your mind is likely to be the pen-like laser pointers you can buy for $10 or less at an electronics or stationary store. But lasers come in many other sizes, shapes, and forms. Most of them are tiny semiconductor chips that we never see because Understanding Lasers: An Entry-Level Guide, Third Edition. By Jeff Hecht Copyright © 2008 the Institute of Electrical and Electronics Engineers, Inc. 1 2 INTRODUCTION AND OVERVIEW they are hidden inside electronic equipment such as CD players, CD-ROM drives, and DVD, or Blu-Ray players. Others are tubes filled with gas that emit laser light. Some are boxes the size of a filing cabinet or a refrigerator that emit powerful beams to cut or drill holes in metal or plastic. The largest lasers fill the interior of a building and generate pulses of light that for a fleeting billionth or trillionth of a second can deliver more power than the whole U.S. electric power grid. Laser output may not be visible; many lasers emit at infrared or ultraviolet wavelengths invisible to the human eye. What makes them all lasers is that they generate light in the same way, by a process called "light amplification by the stimulated emission of radiation." The word "LASER" is an acronym for that phrase. It is the process of amplifying stimulated emission that makes laser light special. The sun, light bulbs, flames, and other light sources emit light in a different way, spontaneously. That leads to important differences between laser light and other kinds of light, which we will explain later. Most of us also are familiar with fictional weapons that resemble lasers and sometimes are called lasers. The deadly heat rays used by the Martian invaders of Earth in The War of the Worlds seem uncannily like lasers, emitting beams of invisible infrared light. Yet H. G. Wells wrote the book in 1896, long before anyone had thought of stimulated emission or lasers. Wells just imagined a searchlight beam that could burn rather than illuminate. Pulp science fiction writers soon churned out tales of ray guns or death rays, which fired deadly beams of light or other (often undefined) forms of radiation. The writers may have heard rumors that legendary inventor Nikola Tesla and a handful of other scientists were working on death rays in the 1920s and 1930s, but there was no real science behind their weapons. They were just futuristic props to avoid arming 25th century heroes with six-shooters. But thanks to those stories, when the laser was invented the public thought of it as a "death ray," much to the annoyance of the people working with real lasers. It is true that military researchers are trying to develop laser weapons. That is not new; it has been going on since the 1960s and so far has consumed many billions of dollars to shoot down a few targets. As you will learn in Section 12.8, laser weapons are big, and they try to destroy targets by focusing a lot of light energy on them. In short, it is not easy to make lasers into weapons. 1.2 WHAT IS A LASER? 3 This book is about real lasers, so we will start by looking at the fundamental concepts behind real-world laser technology, briefly explaining what they are and how they developed. 1.2 WHAT IS A LASER? You have already seen than the word "laser" is shorthand for the phrase "light amplification by the stimulated emission of radiation." Each part of that phrase has a special meaning, so we will look at it piece by piece, starting from the end. Radiation means electromagnetic radiation, a massless form of energy that travels at the speed of light. It comes in various forms, including visible light, infrared, ultraviolet, radio waves, microwaves, and X-rays. Light and other forms of electromagnetic radiation behave like both waves and particles (called photons). You will learn more about the details in Chapter 2. Stimulated emission tells us that laser light is produced in a special way. Ordinarily, atoms or molecules spontaneously emit energy in the form of light or other types of electromagnetic radiation. The sun, flames, and fluorescent lamps all release energy by emitting light spontaneously. However, in certain cases atoms and molecules can be stimulated to emit that extra energy as light. This process is called stimulated emission, and you will learn more about it in Chapter 3. Amplification means increasing the amount of light. In stimulated emission, an input wave stimulates an atom or molecule to release energy as a second wave, which is perfectly matched to the input wave. The stimulated wave, in turn, can stimulate other atoms or molecules to emit duplicate waves, causing further amplification. It may be easier to think of stimulated emission as one light photon stimulating an atom or molecule to emit an identical photon, which in turn can stimulate the emission of another identical photon. In both cases the result is amplification, producing more light. Light describes the type of electromagnetic radiation produced. In practice, that means not just light visible to the human eye, but also electromagnetic radiation that our eyes cannot see because it is either longer in wavelength (infrared) or shorter in wavelength (ultraviolet.) It took a long time to put the pieces of the idea together. Albert Einstein first suggested the possibility of stimulated emis- 4 INTRODUCTION AND OVERVIEW sion in a paper published in 1917. Although stimulated emission was first observed in the 1920s, physicists long thought that spontaneous emission was much more likely, so stimulated emission would always be much weaker. The first hints that stimulated emission could be stronger came in radio experiments shortly after World War II, but the key experiment came in the 1950s. Charles H. Townes, then at Columbia University, conceived of a way to build up stimulated emission at microwave frequencies in 1951. His idea was to isolate ammonia molecules with extra energy, then stimulate them to emit their extra energy at a particular microwave frequency as they were passing through a cavity that reflected the microwave frequency emitted by the ammonia molecules. He called his device a "maser," an acronym for microwave amplification by the stimulated emission of radiation. It took until 1954 for Townes and his graduate student James Gordon to make the maser work. It could serve either as an amplifier or an oscillator. Some ammonia molecules spontaneously emitted microwaves at a frequency of 24 gigahertz, and that spontaneous emission could stimulate other excited ammonia molecules to emit at the same frequency, building up a signal that oscillated on its own. Alternatively, an external 24-GHz signal could stimulate the ammonia molecules to emit at 24 GHz, amplifying the signal. In principle, the maser process could be extended to other types of electromagnetic radiation if the right materials could be found. The next logical step was to optical wavelengths, and a number of people thought seriously about the possibility. However Townes was the first to start serious research in 1957. In the course of gathering information, he talked with Gordon Gould, a Columbia graduate student who was using an important new idea called optical pumping in his doctoral research project. Townes thought he could use optical pumping to excite atoms in a laser, and the laser idea intrigued Gould. Townes went on to enlist the help of his brother-in-law, Arthur Schawlow, who knew more about optics, to work out how to amplify stimulated emission of light. Meanwhile Gould quietly tackled the problem with a pile of reference books on his kitchen table. They essentially independently solved the same physics problem, and both proposed building cylindrical laser resonators with mirrors on opposite ends so the light would 1.2 W H A T IS A LASER? 5 bounce back and forth between the mirrors while it was being amplified. Gould set out to patent the his ideas; Townes and Schawlow published their proposal in a scientific journal, Physical Review Letters. Their work launched a race to build a laser, which I chronicled in Beam: The Race to Make the Laser (Oxford University Press 2005). Townes shared in the 1964 Nobel Prize in physics for his pioneering work on "the maser/laser principle," and after a long series of legal battles, Gould earned tens of millions of dollars from his patent claims. However, the winner of the laser race was Theodore Maiman, who on May 16, 1960 produced laser pulses from a fingertip-sized crystal of synthetic ruby at Hughes Research Laboratories in Malibu, California. Figure 1-1 shows Maiman and Figure 1-1. Theodore Maiman and Irnee J. D'Haenens with a replica of the world's first laser, which they made at Hughes Research Laboratories in 1960. (Reprinted from Hughes Research Laboratories, courtesy of AIP Neils Bohr Library.) 6 INTRODUCTION AND OVERVIEW his assistant Irnee D'Haenens holding a replica of his elegant little device, the world's first laser. The ruby laser was in many ways typical of the many other types of lasers that followed it. Energy from an external source—in this case, a bright flash of light from a photographic flash lamp— excited chromium atoms in a ruby cylinder. Some excited chromium atoms spontaneously emitted light, and that light stimulated other excited chromium atoms to release their excess energy as an identical light wave. Silver film mirrors coated onto the ends of the ruby rod formed a resonant cavity, so light bounced back and forth between them, stimulating more emission from chromium atoms and amplifying the red light to build up a beam. The laser beam emerged through a hole in one of the silver coatings on the ends of the rod. The laser light was at a single wavelength—694 nanometers (1 nm = 1CT9 meter) at the red end of the visible spectrum. The light waves were coherent, all aligned with each other and marching along in step. The lasers that followed generally shared key properties of the ruby laser, generating coherent beams of monochromatic light. LASER OSCILLATION Stimulated emission amplifies light in a laser, but the laser itself is an oscillator. So why, you may wonder, does the word "laser" come from "light amplification by the stimulated emission of radiation"? There's an interesting bit of history behind that. Charles Townes created the word "maser" as an acronym for microwave amplification by the stimulated emission of radiation. When he began thinking of an optical version of the maser, he called it an optical maser. When Gordon Gould sat down to tackle the same problem, he wrote "laser" at the top of his notes, inventing the acronym for light amplification. As the competition between Townes and Gould became intense, each side pushed its own term. Arthur Schawlow was a jovial soul, and at one conference pointed out that because the laser was actually an oscillator, it should be described as "light oscillation by the stimulated emission of radiation," making the laser a "loser." Everybody laughed, but the word laser proved a winner. 1.3 LASER MATERIALS A N D TYPES 7 Maiman's ruby laser was pulsed; many others generated continuous beams. Some generated stimulated emission from longer, thinner rods of other crystals. Others stimulated emission from gases inside a tube with mirrors at its two ends. The most common lasers today are tiny chips of semiconductor compounds such as gallium arsenide. But some lasers occupy entire rooms in buildings, and the most powerful lasers—like the U.S. Air Force's Airborne Laser—occupy whole buildings or aircraft. Lasers operate at wavelengths from the infrared all the way to soft X-rays. They can generate modest powers far below one watt, steady powers of thousands of watts, or concentrate light into pulses lasting less than a billionth of a second. Figure 1-2 shows commercial gas, semiconductor, and solid-state lasers designed for a variety of applications. 1.3 LASER MATERIALS AND TYPES Maiman won the laser race because he had studied the optical properties of ruby, and carefully designed his laser to take advantage of them. Matching the laser design to the material properties was critical. Most materials won't work as lasers under most conditions. What is needed is a material containing atoms or molecules that can be excited into a state ready to be stimulated to emit light energy. Ruby worked because it contains chromium atoms, which absorb energy as visible light, then eventually release much of that energy as a photon of red light. Maiman found that if he slipped a ruby rod inside a coiled flash lamp, the bright flash would excite most of the chromium atoms, leaving them ready to emit red light. If one chromium atom spontaneously emitted a red photon, that photon could stimulate another chromium atom to emit a second photon; and both of those photons could stimulate more emission, eventually producing a cascade of red light in a laser pulse. Figure 1-3 shows the basic idea. Ruby is an important example of a solid-state laser. In these lasers, light from an external source, such as a flash lamp, excites atoms distributed within a solid. The solid must be transparent at the wavelength of the pump light so it can excite the atoms that produce the stimulated emission. In ruby, the transparent material is sapphire (aluminum oxide or Al 2 0 3 ) and the light emitting 8 INTRODUCTION AND OVERVIEW Figure 1-2. A sampling of commercial lasers. (A) A sampling of milliwatt-class helium-neon lasers, including both packaged heads and bare tubes (courtesy JDS Uniphase). (B) A sampling of commercial diode lasers packaged for various types of applications (courtesy of Spectra-Physics, a division of Newport Corporation). atoms are chromium. Another common choice is adding a rareearth element called neodymium to transparent materials such as the crystal yttrium-aluminum garnet (YAG) or certain types of glass. Two other rare-earth elements, erbium and ytterbium, can be added to glass that is drawn into optical fibers, to produce solid-state fiber lasers.

Author Jeff Hecht Isbn 9780470088906 File size 37MB Year 2008 Pages 496 Language English File format PDF Category Physics Book Description: FacebookTwitterGoogle+TumblrDiggMySpaceShare Updated to reflect advancements since the publication of the previous edition, Understanding Lasers: An Entry-Level Guide, 3rd Edition is an introduction to lasers and associated equipment. You need only a minimal background in algebra to understand the nontechnical language in this book, which is a practical, easy-to-follow guide for beginners. By studying the conceptual drawings, tables, and multiple-choice quizzes with answers provided at the back of the book you can understand applications of semiconductor lasers, solid-state lasers, and gas lasers for information processing, medicine, communications, industry, and military systems.     Download (37MB) Field Guide to Lasers Femtosecond Laser-Matter Interaction: Theory, Experiments and Applications Light Sources, Second Edition: Basics Of Lighting Technologies And Applications Statistical Thermodynamics: Understanding The Properties Of Macroscopic Systems Plasma Harmonics Load more posts

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