Fundamentals of light sources and lasers

349 Pages·2004·3.663 MB·English

by  Mark Csele

FUNDAMENTALS OF LIGHT
SOURCES AND LASERS
FUNDAMENTALS OF LIGHT
SOURCES AND LASERS
Mark Csele
A JOHN WILEY & SONS, INC., PUBLICATION
Copyright#2004byJohnWiley&Sons,Inc.Allrightsreserved.
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LibraryofCongressCataloging-in-PublicationData:
Csele,Mark.
Fundamentalsoflightsourcesandlasers/MarkCsele.
p.cm.
“AWiley-Intersciencepublication.”
Includesbibliographicalreferencesandindex.
ISBN0-471-47660-9(cloth:acid-freepaper)
1.Lightsources.2.Lasers.I.Title.
QC355.3.C742004
621.3606--dc22
2004040908
PrintedintheUnitedStatesofAmerica
10 9 8 7 6 5 4 3 2 1
To my parents
for fostering and encouraging
my interest in science
&CONTENTS
Preface xiii
1. Light and Blackbody Emission 1
1.1 Emission ofThermal Light 1
1.2 Electromagnetic Spectrum 2
1.3 Blackbody Radiationand the Stefan–Boltzmann Law 2
1.4 Wein’s Law 4
1.5 CavityRadiation andCavity Modes 6
1.6 Quantum Nature ofLight 9
1.7 Electromagnetic Spectrum Revisited 10
1.8 Absorption and Emission Processes 10
1.9 Boltzmann Distributionand Thermal Equilibrium 13
1.10 Quantum View ofBlackbody Radiation 14
1.11 Blackbodies at VariousTemperatures 15
1.12 Applications 17
1.13 Absorption and Color 18
1.14 EfficiencyofLight Sources 18
Problems 19
2. Atomic Emission 21
2.1 Line Spectra 21
2.2 Spectroscope 22
2.3 Einstein andPlanck:E¼hn 26
2.4 Photoelectric Effect 27
2.5 Atomic Models and Light Emission 28
2.6 Franck–Hertz Experiment 31
2.7 Spontaneous Emission andLevel Lifetime 34
2.8 Fluorescence 35
2.9 SemiconductorDevices 37
2.10 Light-Emitting Diodes 44
Problems 48
3. QuantumMechanics 49
3.1 Limitations of the Bohr Model 50
3.2 Wave Properties ofParticles (Duality) 50
vii
viii CONTENTS
3.3 Evidence of Wave Properties inElectrons 52
3.4 Wavefunctionsand the Particle-in-a-Box Model 53
3.5 ReconcilingClassical and QuantumMechanics 55
3.6 Angular Momentum inQuantumStates 56
3.7 Spectroscopic Notationand Electron Configuration 57
3.8 Energy Levels Described by Orbital AngularMomentum 60
3.9 MagneticQuantum Numbers 62
3.10 DirectEvidenceofMomentum: The Stern–Gerlach
Experiment 63
3.11 Electron Spin 65
3.12 Summary ofQuantum Numbers 67
3.13 Example ofQuantum Numbers: TheSodiumSpectrum 69
3.14 Multiple Electrons: TheMercury Spectrum 71
3.15 Energy Levels andTransitions in Gas Lasers 72
3.16 Molecular Energy Levels 73
3.17 InfraredSpectroscopy Applications 77
Problems 79
4. LasingProcesses 83
4.1 Characteristics ofCoherent Light 84
4.2 Boltzmann Distribution and Thermal Equilibrium 86
4.3 Creating anInversion 87
4.4 StimulatedEmission 90
4.5 Rate Equations and Criteria for Lasing 92
4.6 Laser Gain 98
4.7 Linewidth 101
4.8 Thresholds for Lasing 104
4.9 Calculating Threshold Gain 106
Problems 113
5. LasingTransitions and Gain 117
5.1 Selective Pumping 117
5.2 Three-and Four-Level Lasers 119
5.3 CW LasingAction 124
5.4 Thermal Population Effects 127
5.5 Depopulation ofLowerEnergy Levels in
Four-Level Lasers 128
5.6 Rate Equation Analysis for Atomic Transitions 130
5.7 Rate Equation Analysis for Three- and
Four-Level Lasers 136
5.8 Gain Revisited 143
5.9 Saturation 146
5.10 RequiredPump Power and Efficiency 149
CONTENTS ix
5.11 Output Power 154
Problems 156
6. Cavity Optics 159
6.1 Requirementsfor a Resonator 159
6.2 Gain and Loss in aCavity 160
6.3 Resonatoras anInterferometer 162
6.4 Longitudinal Modes 164
6.5 Wavelength Selection inMultiline Lasers 166
6.6 Single-FrequencyOperation 169
6.7 Characterizationof aResonator 174
6.8 Gaussian Beam 176
6.9 ResonatorStability 178
6.10 Common Cavity Configurations 180
6.11 Spatial Energy Distributions: Transverse Modes 185
6.12 Limiting Modes 186
6.13 ResonatorAlignment: APractical Approach 187
Problems 190
7. Fast-PulseProduction 193
7.1 Concept ofQ-Switching 193
7.2 Intracavity Switches 195
7.3 Energy Storage inLaser Media 196
7.4 Pulse Power andEnergy 198
7.5 Electrooptic Modulators 202
7.6 Acoustooptic Modulators 206
7.7 CavityDumping 211
7.8 Modelocking 212
7.9 Modelocking inthe Frequency Domain 215
Problems 217
8. NonlinearOptics 219
8.1 Linearand Nonlinear Phenomena 219
8.2 Phase Matching 223
8.3 Nonlinear Materials 227
8.4 SHG Efficiency 229
8.5 Sum andDifference Optical Mixing 230
8.6 Higher-Order Nonlinear Effects 231
8.7 Optical ParametricOscillators 232
Problems 233
x CONTENTS
9. Visible Gas Lasers 235
9.1 Helium–Neon Lasers 235
9.2 LasingMedium 236
9.3 Opticsand Cavities 237
9.4 Laser Structure 239
9.5 HeNe Power Supplies 241
9.6 Output Characteristics 245
9.7 Applications 246
9.8 Ion Lasers 247
9.9 LasingMedium 247
9.10 Opticsand Cavities 251
9.11 Laser Structure 252
9.12 PowerSupplies 256
9.13 Output Characteristics 258
9.14 Applications and Operation 259
10. UV Gas Lasers 261
10.1 Nitrogen Lasers 261
10.2 LasingMedium 262
10.3 Gain andOptics 264
10.4 Nitrogen Laser Structure 265
10.5 Output Characteristics 269
10.6 Applications and Practical Units 269
10.7 Excimer Lasers 270
10.8 LasingMedium 271
10.9 Gain andOptics 274
10.10 Excimer Laser Structure 274
10.11 Applications 277
10.12 Practical andCommercial Units 278
11. Infrared Gas Lasers 283
11.1 Carbon DioxideLasers 283
11.2 LasingMedium 283
11.3 Opticsand Cavities 285
11.4 Structure of aLongitudinal CO Laser 286
2
11.5 Structure of aTransverse CO Laser 289
2
11.6 Alternative Structures 290
11.7 PowerSupplies 290
11.8 Output Characteristics 292
11.9 Applications 292
11.10 Far-IRLasers 293
CONTENTS xi
12. Solid-State Lasers 295
12.1 RubyLasers 295
12.2 LasingMedium 296
12.3 Opticsand Cavities 297
12.4 Laser Structure 298
12.5 PowerSupplies 299
12.6 Output Characteristics 300
12.7 Applications 301
12.8 YAG (Neodymium) Lasers 301
12.9 LasingMedium 302
12.10 Opticsand Cavities 302
12.11 Laser Structure 303
12.12 PowerSupplies 306
12.13 Applications,Safety,and Maintenance 308
12.14 Fiber Amplifiers 309
13. Semiconductor Lasers 313
13.1 LasingMedium 313
13.2 Laser Structure 315
13.3 Optics 319
13.4 PowerSupplies 320
13.5 Output Characteristics 321
13.6 Applications 324
14. Tunable Dye Lasers 327
14.1 LasingMedium 327
14.2 Laser Structure 330
14.3 Opticsand Cavities 334
14.4 Output Characteristics 334
14.5 Applications 335
Index 337
&PREFACE
Thefieldofphotonicsisenormouslybroad,coveringeverythingfromlightsources
togeometricandwaveopticstofiberoptics.Laserandlightsourcetechnologyisa
subsetofphotonicswhoseimportanceisoftenunderestimated.Thisbookfocuseson
these technologies with a good degree of depth, without attempting to be overly
broad and all-inclusive of various photonics concepts. For example, fiber optics is
largely omitted in this book except when relevant, such as when fiber amplifiers
areexamined.Readersshouldfindthisbookarefreshingmixoftheoryandpractical
examples,withenough mathematicaldetailtoexplainconceptsandenablepredic-
tionofthebehaviorofdevices(e.g.,lasergainandloss)withouttheuseofoverwhel-
mingly complex calculus. Where possible, a graphical approach has been taken to
explainconceptssuchasmodelocking(inChapter7)whichwouldotherwiserequire
many pages ofcalculus todevelop.
This book, targeted primarily to the scientist or engineer using the technology,
offers the reader theory coupled with practical, real-world examples based on real
lasersystems.Webeginwithalookatthebasicsoflightemission,includingblack-
body radiation and atomic emission, followed byan outline ofquantum mechanics.
Forsomereadersthiswillbeabasicreview;however,theavailabilityofbackground
materialalleviatesthenecessitytoreferbackconstantlytoasecond(orthird)bookon
the subject.Throughoutthebook, practical, solvedexamplesfounded onreal-world
lasersystemsallowdirectapplicationofconceptscovered.Casestudiesinlaterchap-
tersallowthereadertofurtherapplyconceptsinthetexttoreal-worldlasersystems.
Thebookisalsoidealforstudentsinanundergraduatecourseonlasersandlight
sources.Indeed,theoriginaldesignwasforatextbookforanapplieddegreecourse
(actually,twocourses)inlaserengineering.Unlikemanyexistingtextswhichcover
this material in a single chapter, this book has depth, allowing the reader to delve
into the intricacies. Chapter problems assist the reader by challenging him or her
to make the jump between theory and reality. The book should serve well as a
textforasinglecourseinlasertechnologyortwocourseswherealaboratorycom-
ponent is present. Introductory chapters on blackbody radiation, atomic emission,
and quantum mechanics allow the book to be used without the requirement of a
second or third book to cover these topics, which are often omitted in similar
texts. It is assumed that students will already have a grasp of geometric and wave
optics (including the concepts of interference and diffraction), as well as basic
first-year physics, including kinematics.
Chapter1beginswithalookatthemostbasiclightsourceofall,blackbodyradi-
ation,andincludesalookatstandardapplicationssuchasincandescentlightingas
xiii