Walter Koechner Solid-State Laser Engineering Fourth Extensively Revised and Updated Edition With 449 Figures Springer
Contents 1. Introduction 1 1.1 Optical Amplification 1 1.2 Interaction of Radiation with Matter 2 1.2.1 Blackbody Radiation 2 1.2.2 Boltzmann Statistics 3 1.2.3 Einstein Coefficients 4 1.2.4 Phase Coherence of Stimulated Emission 7 1.3 Absorption and Optical Gain 8 1.3.1 Atomic Lineshapes 8 1.3.2 Absorption by Stimulated Transitions 13 1.3.3 Population Inversion 15 1.4 Creation of a Population Inversion 17 1.4.1 The Three-Level System 18 1.4.2 The Four-Level System 19 1.4.3 The Metastable Level 20 1.5 Laser Rate Equations 22 2. Properties of Solid-State Laser Materials 28 2.1 Overview 28 2.1.1 Host Materials 29 2.1.2 Active Ions 35 2.2 Ruby 39 2.3 Nd : Lasers 47 2.3.1 Nd:YAG 48 2.3.2 Nd : Glass 54 2.3.3 Nd : Cr : GSGG 57 2.3.4 Nd : YLF 60 2.4 Er : Lasers 63 2.4.1 Er : YAG 63 2.4.2 Er : Glass 64 2.5 Tunable Lasers 66 2.5.1 Alexandrite Laser 70 2.5.2 Ti : Sapphire 76 2.5.3 Cr : LiSAF 78
VHI Contents 3. Laser Oscillator 81 3.1 Operation at Threshold 82 3.2 Gain Saturation 87 3.3 Circulating Power 89 3.4 Oscillator Performance Model 90 3.4.1 Energy-Transfer Mechanisms 91 3.4.2 Laser Output 97 3.5 Relaxation Oscillations 106 3.5.1 Theory 106 3.5.2 Spike Suppression in Solid-State Lasers 109 3.5.3 Gain Switching 110 3.6 Examples of Regenerative Oscillators Ill 3.6.1 Ruby Ill 3.6.2 Nd : Glass 117 3.6.3 Nd:YAG 118 3.6.4 Alexandrite 125 3.6.5 Laser-Diode-Pumped Systems 127 3.7 Travelling-Wave Oscillator 140 4. Laser Amplifier 144 4.1 Pulse Amplification 146 4.1.1 Ruby Amplifiers 152 4.1.2 Nd : Glass Amplifiers 157 4.1.3 Nd : YAG Amplifiers 163 4.2 Steady-State Amplification 170 4.2.1 Ruby Amplifier 172 4.2.2 Nd : Glass Amplifier 173 4.3 Signal Distortion 174 4.3.1 Spatial Distortions 174 4.3.2 Temporal Distortions 180 4.4 Gain Limitation and Amplifier Stability 181 4.4.1 Amplified Spontaneous Emission 182 4.4.2 Prelasing and Parasitic Modes 186 5. Optical Resonator 189 5.1 Transverse Modes 189 5.1.1 Intensity Distribution of Transverse Modes 189 5.1.2 Characteristics of a Gaussian Beam 192 5.1.3 Resonator Configurations 195 5.1.4 Stability of Laser Resonators 200 5.1.5 Diffraction Losses 201 5.1.6 Higher-Order Modes 203 5.1.7 Active Resonator 204 5.1.8 Resonator Sensitivity 206
, Contents IX 5.1.9 Mode-Selecting Techniques 210 5.1.10 Examples of Advanced Stable Resonator Designs... 217 5.2 Longitudinal Modes 228 5.2.1 Fabry-Perot Resonators 228 5.2.2 Spectral Characteristics of the Laser Output 235 5.2.3 Axial Mode Control 241 5.3 Temporal and Spectral Stability 252 5.3.1 Amplitude Fluctuations 252 5.3.2 Frequency Control 256 5.4 Hardware Design 259 5.5 Unstable Resonators 262 5.5.1 Confocal Positive-Branch Unstable Resonator 265 5.5.2 Negative-Branch Unstable Resonators 268 5.5.3 Variable Reflectivity Output Couplers 270 5.5.4 Gain, Mode Size and Alignment Sensitivity 276 5.6 Wavelength Selection 278 6. Optical Pump Systems 281 6.1 Pump Sources 281 6.1.1 Noble Gas Flashlamps 285 6.1.2 Continuous Arc Lamps 299 6.1.3 Tungsten-Filament Lamps 306 6.1.4 Laser Diodes 308 6.1.5 Nonelectric Pump Sources 325 6.2 Power Supplies 326 6.2.1 Operation of Laser-Diode Arrays 327 6.2.2 Operation of Arc Lamps 330 6.3 Pump Cavities 348 6.3.1 Pump Configurations for Arc Lamps and Laser Diodes 350 6.3.2 Energy Transfer Characteristics 366 6.3.3 Mechanical Design 379 7. Thermo-Optic Effects and Heat Removal 393 7.1 Cylindrical Geometry 393 7.1.1 CW Operation 394 7.1.2 Single-Shot Operation 413 7.1.3 Repetitively Pulsed Lasers 416 7.2 Cooling Techniques 426 7.2.1 Liquid Cooling 426 7.2.2 Air or Gas Cooling 430 7.2.3 Conductive Cooling 432 7.3 Slab and Disc Geometries 433 7.4 End-Pumped Configurations 449
X Contents 8. Q-Switching 452 8.1 Q-Switch Theory 452 8.2 Mechanical Devices 462 8.3 Electrooptical Q-Switches 465 8.4 Acoustooptic Q-Switches 483 8.5 Dye Q-Switch 489 8.6 Cavity Dumping 494 9. Mode Locking 500 9.1 Pulse Formation 501 9.2 Passive Mode Locking 506 9.2.1 Pulsed Passive Mode Locking 507 9.2.2 Continuous Wave Passive Mode Locking 514 9.3 Active Mode Locking 525 9.3.1 CW Mode Locking 525 9.3.2 Transient Active Mode Locking 529 9.4 Picosecond Lasers 533 9.4.1 Oscillators 533 9.4.2 Regenerative Amplifiers 541 9.5 Femtosecond Lasers 548 9.5.1 Oscillators 548 9.5.2 Chirped Pulse Amplifiers 559 10. Nonlinear Devices 562 10.1 Harmonic Generation 564 10.1.1 Basic Equations of Second-Harmonic Generation... 564 10.1.2 Parameters Affecting the Doubling Efficiency 572 10.1.3 Properties of Nonlinear Crystals 578 10.1.4 Intracavity Frequency Doubling 585 10.1.5 Third-Harmonic Generation 593 10.1.6 Examples of Harmonic Generation 595 10.2 Parametric Oscillators 600 10.2.1 Performance Modeling 604 10.2.2 Materials 616 10.2.3 Design and Performance of Optical Parametric Oscillators 618 10.3 Raman Laser 622 10.3.1 Theory 622 10.3.2 Device Implementation 625 10.3.3 Examples of Raman-Shifted Lasers 627 10.4 Optical Phase Conjugation 631 10.4.1 Basic Considerations 631 10.4.2 Material Properties 633
Contents XI 10.4.3 Focusing Geometry 635 10.4.4 Pump Beam Properties 636 10.4.5 System Design 638 11. Damage of Optical Elements 642 11.1»Surface Damage 643 11.2 Inclusion Damage 644 11.3 Self-focusing 645 11.4 Damage Threshold of Optical Materials 651 11.4.1 Scaling Laws 651 11.4.2 Laser Materials 653 11.4.3 Damage in Optical Glass 654 11.4.4 Damage Levels for Nonlinear Materials 655 11.4.5 Laser Induced Damage in Dielectric Thin Films... 656 11.5 System Design Considerations 658 Appendix A Laser Safety 661 Appendix В Conversion Factors and Constants 667 References 669 Subject Index 702