1．Introductory Concepts 1
1.1．Spontaneous and Stimulated Emission,Absorption 1
1.2．The Laser Idea 4
1.3．Pumping Schemes 6
1.4．Properties of Laser Beams 8
1.4.1．Monochromaticity 9
1.4.2．Coherence 9
1.4.3．Directionality 10
1.4.4．Brightness 11
1.4.5．Short Time Duration 13
1.5．Types of Lasers 14
1.6．Organization of the Book 14
Problems 15
2．Interaction of Radiation with Atoms and Ions 17
2.1．Introduction 17
2.2．Summary of Blackbody Radiation Theory 17
2.2.1．Modes of a Rectangular Cavity 19
2.2.2．The Rayleigh-Jeans and Planck Radiation Formula 22
2.2.3．Planck's Hypothesis and Field Quantization 24
2.3．Spontaneous Emission 26
2.3.1．Semiclassical Approach 26
2.3.2．Quantum Electrodynamics Approach 30
2.3.3．Allowed and Forbidden Transitions 31
2.4．Absorption and Stimulated Emission 32
2.4.1．Rates of Absorption and Stimulated Emission 32
2.4.2．Allowed and Forbidden Transitions 36
2.4.3．Transition Cross Section,Absorption and Gain Coefficient 37
2.4.4．Einstein Thermodynamic Treatment 41
2.5．Line Broadening Mechanisms 43
2.5.1．Homogeneous Broadening 43
2.5.2．Inhomogeneous Broadening 47
2.5.3．Concluding Remarks 49
2.6．Nonradiative Decay and Energy Transfer 50
2.6.1．Mechanisms of Nonradiative Decay 50
2.6.2．Combined Effects of Radiative and Nonradiative Processes 56
2.7．Degenerate or Strongly Coupled Levels 58
2.7.1．Degenerate Levels 58
2.7.2．Strongly Coupled Levels 60
2.8．Saturation 64
2.8.1．Saturation of Absorption:Homogeneous Line 64
2.8.2．Gain Saturation:Homogeneous Line 67
2.8.3．Inhomogeneously Broadened Line 69
2.9．Decay of an Optically Dense Medium 70
2.9.1．Radiation Trapping 71
2.9.2．Amplified Spontaneous Emission 71
2.10．Concluding Remarks 76
Problems 77
References 78
3．Energy Levels,Radiative and Nonradiative Transitions in Molecules and Semiconductors 81
3.1．Molecules 81
3.1.1．Energy Levels 81
3.1.2．Level Occupation at Thermal Equilibrium 85
3.1.3．Stimulated Transitions 87
3.1.4．Rediative and Nonradiative Decay 91
3.2．Bulk Semiconductors 93
3.2.1．Electronic States 93
3.2.2．Density of States 97
3.2.3．Level Occupation at Thermal Equilibrium 98
3.2.4．Stimulated Transitions 101
3.2.5．Absorption and Gain Coefficients 104
3.2.6．Spontaneous Emission and Nonradiative Decay 110
3.2.7．Concluding Remarks 112
3.3．Semiconductor Quantum Wells 113
3.3.1．Electronic States 113
3.3.2．Density of States 116
3.3.3．Level Occupation at Thermal Equilibrium 118
3.3.4．Stimulated Transitions 119
3.3.5．Absorption and Gain Coefficients 121
3.3.6．Strained Quantum Wells 125
3.4．Quantum Wires and Quantum Dots 126
3.5．Concluding Remarks 128
Problems 128
References 129
4．Ray and Wave Propagation Through Optical Media 131
4.1．Introduction 131
4.2．Matrix Formulation of Geometrical Optics 131
4.3．Wave Reflection and Transmission at a Dielectric Interface 137
4.4．Multilayer Dielectric Coatings 139
4.5．The Fabry-Perot Intefferometer 142
4.5.1．Properties of a Fabry-Perot Interferometer 142
4.5.2．The Fabry-Perot Interferometer as a Spectrometer 146
4.6．Diffraction Optics in the Paraxial Approximation 147
4.7．Gaussian Beams 150
4.7.1．Lowest-Order Mode 150
4.7.2．Free Space Propagation 153
4.7.3．Gaussian Beams and the ABCD Law 156
4.7.4．Higher-Order Modes 158
4.8．Conclusions 159
Problems 159
References 161
5．Passive Optical Resonators 163
5.1．Introduction 163
5.2．Eigenmodes and Eigenvalues 167
5.3．Photon Lifetime and Cavity Q 169
5.4．Stability Condition 171
5.5．Stable Resonators 175
5.5.1．Resonators with Infinite Aperture 175
5.5.1.1．Eigenmodes 176
5.5.1.2．Eigenvalues 180
5.5.1.3．Standing-and Traveling-Waves in a Two-Mirror Resonator 182
5.5.2．Effects of a Finite Aperture 183
5.5.3．Dynamically and Mechanically Stable Resonators 186
5.6．Unstable Resonators 189
5.6.1．Geometrical-Optics Description 190
5.6.2．Wave-Optics Description 192
5.6.3．Advantages and Disadvantages of Hard-Edge Unstable Resonators 196
5.6.4．Variable-Reflectivity Unstable Resonators 196
5.7．Concluding Remarks 200
Problems 200
References 203
6．Pumping Processes 205
6.1．Introduction 205
6.2．Optical Pumpingby an Incoherent Light Source 208
6.2.1．Pumping Systems 208
6.2.2．Absorption of Pump Light 211
6.2.3．Pump Efficiency and Pump Rate 213
6.3．Laser Pumping 215
6.3.1．Laser Diode Pumps 217
6.3.2．Pump Transfer Systems 219
6.3.2.1．Longitudinal Pumping 219
6.3.2.2．Transverse Pumping 224
6.3.3．Pump Rate and Pump Efficiency 225
6.3.4．Threshold Pump Power for Four-Level and Quasi-Three-Level Lasers 228
6.3.5．Comparison Between Diode-pumping and Lamp-pumping 230
6.4．Electrical Pumping 232
6.4.1．Electron Impact Excitation 236
6.4.1.1．Electron Impact Cross Section 237
6.4.2．Thermal and Drift Velocities 240
6.4.3．Electron Energy Distribution 242
6.4.4．The Ionization Balance Equation 245
6.4.5．Scaling Laws for Electrical Discharge Lasers 247
6.4.6．Pump Rate and Pump Efficiency 248
6.5．Conclusions 250
Problems 250
References 253
7．Continuous Wave Laser Behavior 255
7.1．Introduction 255
7.2．Rate Equations 255
7.2.1．Four-Level Laser 256
7.2.2．Quasi-Three-Level Laser 261
7.3．Threshold Conditions and Output Power:Four-Level Laser 263
7.3.1．Space-Independent Model 264
7.3.2．Space-Dependent Model 270
7.4．Threshold Condition and Output Power:Quasi-Three-Level Laser 279
7.4.1．Space-Independent Model 279
7.4.2．Space-Dependent Model 280
7.5．Optimum Output Coupling 283
7.6．Laser Tuning 285
7.7．Reasons for Multimode Oscillation 287
7.8．Single-Mode Selection 290
7.8.1．Single-Transverse-Mode Selection 290
7.8.2．Single-Longitudinal-Mode Selection 291
7.8.2.1．Fabry-Perot Etalons as Mode-Selective Elements 292
7.8.2.2．Single Mode Selection via Unidirectional Ring Resonators 294
7.9 Frequency-Pulling and Limit to Monochromaticity 297
7.10．Laser Frequency Fluctuations and Frequency Stabilization 300
7.11．Intensity Noise and Intensity Noise Reduction 304
7.12．Conclusions 306
Problems 308
References 310
8．Transient Laser Behavior 313
8.1．Introduction 313
8.2．Relaxation Oscillations 313
8.2.1．Linearized Analysis 315
8.3．Dynamical Instabilities and Pulsations in Lasers 318
8.4．Q-Switching 319
8.4.1．Dynamics of the Q-Switching Process 319
8.4.2．Methods of Q-Switching 321
8.4.2.1．Electro-Optical Q-Switching 322
8.4.2.2．Rotating Prisms 323
8.4.2.3．Acousto-Optic Q-Switches 324
8.4.2.4．Saturable-Absorber Q-Switch 325
8.4.3．Operating Regimes 328
8.4.4．Theory of Active Q-Switching 329
8.5．Gain Switching 337
8.6．Mode-Locking 339
8.6.1．Frequency-Domain Description 340
8.6.2．Time-Domain Picture 344
8.6.3．Methods of Mode-Locking 346
8.6.3.1．Active Mode-Locking 346
8.6.3.2．Passive Mode Locking 350
8.6.4．The Role of Cavity Dispersion in Femtosecond Mode-Locked Lasers 356
8.6.4.1．Phase-Velocity,Group-Velocity and Group-Delay-Dispersion 356
8.6.4.2．Limitation on Pulse Duration due to Group-Delay Dispersion 358
8.6.4.3．Dispersion Compensation 360
8.6.4.4．Soliton-type of Mode-Locking 361
8.6.5．Mode-Locking Regimes and Mode-Locking Systems 364
8.7．Cavity Dumping 368
8.8．Concluding Remarks 369
Problems 370
References 372
9．Solid-State,Dye,and Semiconductor Lasers 375
9.1．Introduction 375
9.2．Solid-State Lasers 375
9.2.1．The Ruby Laser 377
9.2.2．Neodymium Lasers 380
9.2.2.1．Nd:YAG 380
9.2.2.2．Nd:Glass 383
9.2.2.3．Other Crystalline Hosts 384
9.2.3．Yb:YAG 384
9.2.4．Er:YAG and Yb:Er:glass 386
9.2.5．Tm:Ho:YAG 387
9.2.6．Fiber Lasers 389
9.2.7．Alexandrite Laser 391
9.2.8．Titanium Sapphire Laser 394
9.2.9．Cr:LISAF and Cr:LICAF 396
9.3．Dye Lasers 397
9.3.1．Photophysical Properties of Organic Dyes 397
9.3.2．Characteristics of Dye Lasers 401
9.4．Semiconductor Lasers 405
9.4.1．Principle of Semiconductor Laser Operation 405
9.4.2．The Homojunction Laser 407
9.4.3．The Double-Heterostructure Laser 408
9.4.4．Quantum Well Lasers 413
9.4.5．Laser Devices and Performances 416
9.4.6．Distributed Feedback and Distributed Bragg Reflector Lasers 419
9.4.7．Vertical Cavity Surface Emitting Lasers 423
9.4.8．Applications of Semiconductor Lasers 425
9.5．Conclusions 427
Problems 427
References 429
10．Gas,Chemical,Free Electron,and X-Ray Lasers 431
10.1．Introduction 431
10.2．Gas Lasers 431
10.2.1．Neutral Atom Lasers 432
10.2.1.1．Helium-Neon Lasers 432
10.2.1.2．Copper Vapor Lasers 437
10.2.2．Ion Lasers 439
10.2.2.1．Argon Laser 439
10.2.2.2．He-Cd Laser 442
10.2.3．Molecular Gas Lasers 444
10.2.3.1．The CO2 Laser 444
10.2.3.2．The CO Laser 454
10.2.3.3．The N2 Laser 456
10.2.3.4．Excimer Lasers 457
10.3．Chemical Lasers 461
10.3.1．The HF Laser 461
10.4．The Free-Electron Laser 465
10.5．X-ray Lasers 469
10.6．Concluding Remarks 471
Problems 471
References 473
11．Properties of Laser Beams 475
11.1．Introduction 475
11.2．Monochromaticity 475
11.3．First-Order Coherence 476
11.3.1．Degree of Spatial and Temporal Coherence 477
11.3.2．Measurement of Spatial and Temporal Coherence 480
11.3.3．Relation Between Temporal Coherence and Monochromaticity 483
11.3.4．Nonstationary Beams 485
11.3.5．Spatial and Temporal Coherence of Single-Mode and Multimode Lasers 485
11.3.6．Spatial and Temporal Coherence of a Thermal Light Source 488
11.4．Directionality 489
11.4.1．Beams with Perfect Spatial Coherence 489
11.4.2．Beams with Partial Spatial Coherence 491
11.4.3．The M2 Factor and the Spot-Size Parameter of a Multimode Laser Beam 492
11.5．Laser Speckle 495
11.6．Brightness 498
11.7．Statistical Properties of Laser Light and Thermal Light 499
11.8．Comparison Between Laser Light and Thermal Light 501
Problems 503
References 504
12．Laser Beam Transformation:Propagation,Amplification,Frequency Conversion,Pulse Compression and Pulse Expansion 505
12.1．Introduction 505
12.2．Spatial Transformation:Propagation of a Multimode Laser Beam 506
12.3．Amplitude Transformation:Laser Amplification 507
12.3.1．Examples of Laser Amplifiers:Chirped-Pulse-Amplification 512
12.4．Frequency Conversion:Second-Harmonic Generation and Parametric Oscillation 516
12.4.1．Physical Picture 516
12.4.1.1．Second-Harmonic Generation 517
12.4.1.2．Parametric Oscillation 524
12.4.2．Analytical Treatment 526
12.4.2.1．Parametric Oscillation 528
12.4.2.2．Second-Harmonic Generation 532
12.5．Transformation in Time:Pulse Compression and Pulse Expansion 535
12.5.1．Pulse Compression 536
12.5.2．Pulse Expansion 541
Problems 543
References 544
Appendices 547
A．Semiclassical Treatment of the Interaction of Radiation with Matter 547
B．Lineshape Calculation for Collision Broadening 553
C．Simplified Treatment of Amplified Spontaneous Emission 557
References 560
D．Calculation of the Radiative Transition Rates of Molecular Transitions 561
E．Space Dependent Rate Equations 565
E.1．Four-Level Laser 565
E.2．Quasi-Three-Level Laser 571
F．Theory of Mode-Locking:Homogeneous Line 575
F.1．Active Mode-Locking 575
F.2．Passive Mode-Locking 580
References 581
G．Propagation of a Laser Pulse Through a Dispersive Medium or a Gain Medium 583
References 587
H．Higher-Order Coherence 589
I．Physical Constants and Useful Conversion Factors 593
Answers to Selected Problems 595
Index 607