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Preface xiii 1 Introduction to Laser Operation 1
1.1 Introduction 1
1.2 Lasers and Laser Light 3
1.3 Light in Cavities 8
1.4 Light Emission and Absorption in Quantum Theory 10
1.5 Einstein Theory of Light-Matter Interactions 11
1.6 Summary 14 2 Atoms, Molecules, and Solids 17
2.1 Introduction 17
2.2 Electron Energy Levels in Atoms 17
2.3 Molecular Vibrations 26
2.4 Molecular Rotations 31
2.5 Example: Carbon Dioxide 33
2.6 Conductors and Insulators 35
2.7 Semiconductors 39
2.8 Semiconductor Junctions 45
2.9 Light-Emitting Diodes 49
2.10 Summary 55 Appendix: Energy Bands in Solids 56 Problems 64 3 Absorption, Emission, and Dispersion of Light 67
3.1 Introduction 67
3.2 Electron Oscillator Model 69
3.3 Spontaneous Emission 74
3.4 Absorption 78
3.5 Absorption of Broadband Light 84
3.6 Thermal Radiation 85
3.7 Emission and Absorption of Narrowband Light 93
3.8 Collision Broadening 99
3.9 Doppler Broadening 105
3.10 The Voigt Profile 108
3.11 Radiative Broadening 112
3.12 Absorption and Gain Coefficients 114
3.13 Example: Sodium Vapor 118
3.14 Refractive Index 123
3.15 Anomalous Dispersion 129
3.16 Summary 132 Appendix: The Oscillator Model and Quantum Theory 132 Problems 137 4 Laser Oscillation: Gain and Threshold 141
4.1 Introduction 141
4.2 Gain and Feedback 141
4.3 Threshold 143
4.4 Photon Rate Equations 148
4.5 Population Rate Equations 150
4.6 Comparison with
Chapter 1 152
4.7 Three-Level Laser Scheme 153
4.8 Four-Level Laser Scheme 156
4.9 Pumping Three- and Four-Level Lasers 157
4.10 Examples of Three- and Four-Level Lasers 159
4.11 Saturation 161
4.12 Small-Signal Gain and Saturation 164
4.13 Spatial Hole Burning 167
4.14 Spectral Hole Burning 169
4.15 Summary 172 Problems 173 5 Laser Oscillation: Power and Frequency 175
5.1 Introduction 175
5.2 Uniform-Field Approximation 175
5.3 Optimal Output Coupling 178
5.4 Effect of Spatial Hole Burning 180
5.5 Large Output Coupling 183
5.6 Measuring Gain and Optimal Output Coupling 187
5.7 Inhomogeneously Broadened Media 191
5.8 Spectral Hole Burning and the Lamb Dip 192
5.9 Frequency Pulling 194
5.10 Obtaining Single-Mode Oscillation 198
5.11 The Laser Linewidth 203
5.12 Polarization and Modulation 207
5.13 Frequency Stabilization 215
5.14 Laser at Threshold 220 Appendix: The Fabry-Pérot Etalon 223 Problems 226 6 Multimode and Pulsed Lasing 229
6.1 Introduction 229
6.2 Rate Equations for Intensities and Populations 229
6.3 Relaxation Oscillations 230
6.4 Q Switching 233
6.5 Methods of Q Switching 236
6.6 Multimode Laser Oscillation 237
6.7 Phase-Locked Oscillators 239
6.8 Mode Locking 242
6.9 Amplitude-Modulated Mode Locking 246
6.10 Frequency-Modulated Mode Locking 248
6.11 Methods of Mode Locking 251
6.12 Amplification of Short Pulses 255
6.13 Amplified Spontaneous Emission 258
6.14 Ultrashort Light Pulses 264 Appendix: Diffraction of Light by Sound 265 Problems 266 7 Laser Resonators and Gaussian Beams 269
7.1 Introduction 269
7.2 The Ray Matrix 270
7.3 Resonator Stability 274
7.4 The Paraxial Wave Equation 279
7.5 Gaussian Beams 282
7.6 The ABCD Law for Gaussian Beams 288
7.7 Gaussian Beam Modes 292
7.8 Hermite-Gaussian and Laguerre-Gaussian Beams 298
7.9 Resonators for He-Ne Lasers 306
7.10 Diffraction 309
7.11 Diffraction by an Aperture 312
7.12 Diffraction Theory of Resonators 317
7.13 Beam Quality 320
7.14 Unstable Resonators for High-Power Lasers 321
7.15 Bessel Beams 322 Problems 327 8 Propagation of Laser Radiation 331
8.1 Introduction 331
8.2 The Wave Equation for the Electric Field 332
8.3 Group Velocity 336
8.4 Group Velocity Dispersion 340
8.5 Chirping 351
8.6 Propagation Modes in Fibers 355
8.7 Single-Mode Fibers 361
8.8 Birefringence 365
8.9 Rayleigh Scattering 372
8.10 Atmospheric Turbulence 377
8.11 The Coherence Diameter 379
8.12 Beam Wander and Spread 388
8.13 Intensity Scintillations 392
8.14 Remarks 395 Problems 397 9 Coherence in Atom-Field Interactions 401
9.1 Introduction 401
9.2 Time-Dependent Schrödinger Equation 402
9.3 Two-State Atoms in Sinusoidal Fields 403
9.4 Density Matrix and Collisional Relaxation 408
9.5 Optical Bloch Equations 414
9.6 Maxwell-Bloch Equations 420
9.7 Semiclassical Laser Theory 428
9.8 Resonant Pulse Propagation 432
9.9 Self-Induced Transparency 438
9.10 Electromagnetically Induced Transparency 441
9.11 Transit-Time Broadening and the Ramsey Effect 446
9.12 Summary 451 Problems 452 10 Introduction to Nonlinear Optics 457
10.1 Model for Nonlinear Polarization 457
10.2 Nonlinear Susceptibilities 459
10.3 Self-Focusing 464
10.4 Self-Phase Modulation 469
10.5 Second-Harmonic Generation 471
10.6 Phase Matching 475
10.7 Three-Wave Mixing 480
10.8 Parametric Amplification and Oscillation 482
10.9 Two-Photon Downconversion 486
10.10 Discussion 492 Problems 494 11 Some Specific Lasers and Amplifiers 497
11.1 Introduction 497
11.2 Electron-Impact Excitation 498
11.3 Excitation Transfer 499
11.4 He-Ne Lasers 502
11.5 Rate Equation Model of Population Inversion in He-Ne Lasers 505
11.6 Radial Gain Variation in He-Ne Laser Tubes 509
11.7 CO2 Electric-Discharge Lasers 513
11.8 Gas-Dynamic Lasers 515
11.9 Chemical Lasers 516
11.10 Excimer Lasers 518
11.11 Dye Lasers 521
11.12 Optically Pumped Solid-State Lasers 525
11.13 Ultrashort, Superintense Pulses 532
11.14 Fiber Amplifiers and Lasers 537
11.15 Remarks 553 Appendix: Gain or Absorption Coefficient for Vibrational-Rotational Transitions 554 Problems 558 12 Photons 561
12.1 What is a Photon 561
12.2 Photon Polarization: All or Nothing 562
12.3 Failures of Classical Theory 563
12.4 Wave Interference and Photons 567
12.5 Photon Counting 569
12.6 The Poisson Distribution 573
12.7 Photon Detectors 575
12.8 Remarks 585 Problems 586 13 Coherence 589
13.1 Introduction 589
13.2 Brightness 589
13.3 The Coherence of Light 592
13.4 The Mutual Coherence Function 595
13.5 Complex Degree Of Coherence 598
13.6 Quasi-Monochromatic Fields and Visibility 601
13.7 Spatial Coherence of Light From Ordinary Sources 603
13.8 Spatial Coherence of Laser Radiation 608
13.9 Diffraction of Laser Radiation 610
13.10 Coherence and the Michelson Interferometer 611
13.11 Temporal Coherence 613
13.12 The Photon Degeneracy Factor 616
13.13 Orders of Coherence 619
13.14 Photon Statistics of Lasers and Thermal Sources 620
13.15 Brown-Twiss Correlations 627 Problems 634 14 Some Applications of Lasers 637
14.1 Lidar 637
14.2 Adaptive Optics for Astronomy 648
14.3 Optical Pumping and Spin-Polarized Atoms 658
14.4 Laser Cooling 671
14.5 Trapping Atoms with Lasers and Magnetic Fields 685
14.6 Bose-Einstein Condensation 690
14.7 Applications of Ultrashort Pulses 697
14.8 Lasers in Medicine 718
14.9 Remarks 728 Problems 729 15 Diode Lasers and Optical Communications 735
15.1 Introduction 735
15.2 Diode Lasers 736
15.3 Modulation of Diode Lasers 754
15.4 Noise Characteristics of Diode Lasers 760
15.5 Information and Noise 774
15.6 Optical Communications 782 Problems 790 16 Numerical Methods for Differential Equations 793
16.A Fortran Program for Ordinary Differential Equations 793
16.B Fortran Program for Plane-Wave Propagation 796
16.C Fortran Program for Paraxial Propagation 799 Index 809