Prologue ........................................................ 1
References ...................................................... 8
1 Background to Laser Design and General Applications ......... 11
1.1 Basic Principles of Lasers ............................. 11
1.1.1 Stimulated Emission Phenomenon .................. 11
1.1.2 Basic Components of a Laser ..................... 12
1.1.3 Physics of the Generation of Laser Light ........ 14
1.1.4 Relationship Between the Einstein
Coefficients .................................... 17
1.1.5 Lifetime Broadening ............................. 18
1.1.6 Transition Rates for Monochromatic Waves ........ 19
1.1.7 Amplification by an Atomic System ............... 20
1.1.8 The Laser: Oscillation and Amplification ........ 23
1.2 Laser Construction Concepts ............................ 24
1.2.1 Overall Design .................................. 24
1.3 Types of Laser ......................................... 32
1.3.1 Gas Lasers ...................................... 32
1.3.2 Solid-state Lasers .............................. 41
1.3.3 Dye Lasers ...................................... 50
1.3.4 Free-electron Lasers ............................ 51
1.4 Applications of Lasers ................................. 51
1.4.1 Powerful Light .................................. 53
1.4.2 Alignment ....................................... 53
1.4.3 Measurement of Length ........................... 54
1.4.4 Velocity Measurement ............................ 57
1.4.5 Holography ...................................... 61
1.4.6 Speckle Interferometry .......................... 63
1.4.7 Measurement of Atmospheric Pollution and
Dynamics ........................................ 64
1.4.8 Inspection ...................................... 66
1.4.9 Analytical Technique ............................ 67
1.4.10 Recording ....................................... 67
1.4.11 Communications .................................. 71
1.4.12 Heat Source ..................................... 71
1.4.13 Medical Uses .................................... 72
1.4.14 Printing ........................................ 72
1.4.15 Isotope Separation .............................. 73
1.4.16 Atomic Fusion ................................... 73
1.4.17 Stimulated Radioactive Decay? ................... 74
1.5 Market for Laser Applications .......................... 74
References ............................................. 76
2 Basic Laser Optics .......................................... 79
2.1 The Nature of Electromagnetic Radiation ................ 79
2.2 Interaction of Electromagnetic Radiation with Matter ... 81
2.2.1 Nonlinear Effects ............................... 84
2.3 Reflection or Absorption ............................... 89
2.3.1 Effect of Wavelength ............................ 90
2.3.2 Effect of Temperature ........................... 91
2.3.3 Effect of Surface Films ......................... 91
2.3.4 Effect of Angle of Incidence .................... 92
2.3.5 Effect of Materials and Surface Roughness ....... 93
2.4 Refraction ............................................. 94
2.4.1 Scattering ...................................... 96
2.5 Interference ........................................... 97
2.6 Diffraction ............................................ 97
2.7 Laser Beam Characteristics ............................. 98
2.7.1 Wavelength ...................................... 98
2.7.2 Coherence ....................................... 98
2.7.3 Mode and Beam Diameter .......................... 99
2.7.4 Polarisation ................................... 101
2.8 Focusing with a Single Lens ........................... 102
2.8.1 Focused Spot Size .............................. 102
2.8.2 Depth of Focus ................................. 114
2.9 Optical Components .................................... 115
2.9.1 Lens Doublets .................................. 115
2.9.2 Depolarisers ................................... 116
2.9.3 Collimators .................................... 117
2.9.4 Metal Optics ................................... 119
2.9.5 Diffractive Optical Elements - Holographic
Lenses ......................................... 120
2.9.6 Laser Scanning Systems ......................... 121
2.9.7 Fibre Delivery Systems ......................... 121
2.9.8 Liquid Lenses .................................. 125
2.9.9 Graded-index Lenses ............................ 127
2.10 Conclusions ........................................... 127
References ............................................ 128
3 Laser Cutting, Drilling and Piercing ....................... 131
3.1 Introduction .......................................... 131
3.2 The Process - How It Is Done .......................... 133
3.3 Laser Drilling and Piercing ........................... 135
3.3.1 Introduction ................................... 135
3.3.2 Drilling Process Variations .................... 136
3.3.3 Percussion and Single- or Double-shot
Drilling ....................................... 136
3.3.4 Drilling Ceramic-coated Material ............... 149
3.3.1 Trepanning ..................................... 149
3.3.6 Helical Trepanning ............................. 151
3.3.7 Applications of Laser Drilling ................. 152
3.3.8 Monitoring the Drilling Process ................ 155
3.4 Methods of Cutting .................................... 156
3.4.1 Vaporisation Cutting/Drilling .................. 156
3.4.2 Fusion Cutting - Melt and Blow ................. 156
3.4.3 Reactive Fusion Cutting ........................ 163
3.4.4 Controlled Fracture ............................ 164
3.4.5 Scribing ....................................... 165
3.4.6 Cold Cutting ................................... 166
3.4.7 Laser-assisted Oxygen Cutting - the LASOX
Process ........................................ 166
3.5 Theoretical Models of Cutting ......................... 168
3.6 Practical Performance ................................. 168
3.6.1 Beam Properties ................................ 169
3.6.2 Transport Properties ........................... 173
3.6.3 Gas Properties ................................. 176
3.6.4 Material Properties ............................ 180
3.6.5 Practical Tips ................................. 182
3.7 Examples of Applications of Laser Cutting ............. 183
3.7.1 Die Board Cutting .............................. 183
3.7.2 Cutting of Quartz Tubes ........................ 184
3.7.3 Profile Cutting ................................ 184
3.7.4 Cloth Cutting .................................. 184
3.7.5 Aerospace Materials ............................ 184
3.7.6 Cutting Fibre Glass ............................ 185
3.7.7 Cutting Kevlar® ................................ 185
3.7.8 Prototype Car Production ....................... 185
3.7.9 Cutting Alumina and Dielectric Boards .......... 185
3.7.10 Furniture Industry ............................. 185
3.7.11 Cutting Paper .................................. 187
3.7.12 Flexographic Print Rolls ....................... 187
3.7.13 Cutting Radioactive Materials .................. 187
3.7.14 Electronics Applications ....................... 187
3.7.15 Scrap Recovery ................................. 187
3.7.16 Laser Machining ................................ 187
3.7.17 Shipbuilding ................................... 188
3.7.18 The Laser Punch Press .......................... 188
3.7.19 Manufacture of Bikes and Tubular Structures .... 188
3.7.20 Cutting and Welding of Railcars ................ 189
3.8 Costed Example ........................................ 189
3.9 Process Variations .................................... 189
3.9.1 Arc-augmented Laser Cutting .................... 189
3.9.2 Hot Machining .................................. 190
3.10 Future Developments .................................. 191
3.10.1 Higher-powered Lasers .......................... 191
3.10.2 Additional Energy Sources ...................... 191
3.10.3 Improved Coupling .............................. 191
3.10.4 Smaller Spot Size .............................. 192
3.10.5 Increased Drag ................................. 192
3.10.6 Increased Fluidity ............................. 192
3.11 Worked Example of Power Requirement ................... 192
References ............................................ 193
4 Laser Welding .............................................. 199
4.1 Introduction .......................................... 199
4.2 Process Arrangement ................................... 202
4.3 Process Mechanisms - Keyholes and Plasmas ............. 203
4.4 Operating Characteristics ............................. 209
4.4.1 Power .......................................... 209
4.4.2 Spot Size and Mode ............................. 213
4.4.3 Polarisation ................................... 214
4.4.4 Wavelength ..................................... 215
4.4.5 Speed .......................................... 216
4.4.6 Focal Position ................................. 218
4.4.7 Joint Geometries ............................... 219
4.4.8 Gas Shroud and Gas Pressure .................... 224
4.4.9 Effect of Gas Pressure - Due to Velocity and
Environment .................................... 228
4.4.10 Effect of Material Properties .................. 229
4.4.11 Gravity ........................................ 232
4.5 Process Variations .................................... 232
4.5.1 Arc-augmented Laser Welding .................... 232
4.5.2 Twin-beam Laser Welding ........................ 234
4.5.3 Walking and Spinning Beams ..................... 234
4.5.4 Laser Welding of Plastics ...................... 235
4.6 Applications for Laser Welding in General ............. 240
4.7 Costed Example ........................................ 244
References ............................................ 246
5 Theory, Mathematical Modelling and Simulation .............. 251
5.1 Introduction .......................................... 251
5.2 What is a Model? ...................................... 254
5.2.1 Derivation of Fourier's Second Law ............. 255
5.3 Analytical Models with One-dimensional Heat Flow ...... 257
5.4 Analytical Models for a Stationary Point Source ....... 261
5.4.1 The Instantaneous Point Source ................. 261
5.4.2 The Continuous Point Source .................... 262
5.4.3 Sources Other than Point Sources ............... 262
5.5 Analytical Models for a Moving Point Source ........... 263
5.6 Alternative Surface Heating Models .................... 264
5.6.1 The Ashby-Shercliffe Model: The Moving
Hypersurface Line Source ....................... 264
5.6.2 The Davis et al. Model: The Moving Gaussian
Source ......................................... 265
5.7 Analytical Keyhole Models - Line Source Solution ...... 266
5.7.1 Line Source on the Axis of the Keyhole ......... 266
5.7.2 Line Source Around the Surface of a Cylinder:
One-dimensional Transient Model for
Cylindrical Bodies ............................. 268
5.7.3 Analytical Moving Point-Line Source ............ 269
5.8 Three-dimensional Models .............................. 270
5.8.1 Three-dimensional Model for a Semi-infinite
Plate .......................................... 270
5.8.2 Three-dimensional Transient Model for Finite
Slabs .......................................... 271
5.9 Numerical Modelling ................................... 272
5.9.1 Three-dimensional Thermal Model ................ 275
5.9.2 Flow Within the Melt Pool - Convection ......... 277
5.9.3 Pool Shape ..................................... 277
5.9.4 Some Model Results ............................. 281
5.9.5 Effect of Flow on Surface Deformation .......... 282
5.9.6 Model for Flow with Vaporisation ............... 283
5.9.7 Mass Additions - Surface Alloying and
Cladding ....................................... 283
5.10 Modelling Laser Ablation .............................. 284
5.11 Semiquantitative Models ............................... 286
5.12 Conclusions ........................................... 288
References ............................................ 292
6 Laser Surface Treatment .................................... 295
6.1 Introduction .......................................... 295
6.2 Laser Heat Treatment .................................. 297
6.2.1 Heat Flow ...................................... 302
6.2.2 Mass Flow by Diffusion ......................... 304
6.2.3 Mechanism of the Transformation Process ........ 305
6.2.4 Properties of Transformed Steels ............... 307
6.3 Laser Surface Melting ................................. 309
6.3.1 Solidification Mechanisms ...................... 314
6.3.2 Style of Solidification ........................ 314
6.4 Laser Surface Alloying ................................ 318
6.4.1 Process Variations ............................. 318
6.4.2 Applications ................................... 320
6.5 Laser Cladding ........................................ 320
6.5.1 Laser Cladding with Preplaced Powder ........... 322
6.5.2 Blown Powder Laser Cladding .................... 323
6.5.3 Applications ................................... 328
6.6 Particle Injection .................................... 329
6.7 Laser-assisted Cold Spray Process ..................... 330
6.8 Surface Texturing ..................................... 330
6.9 Enhanced Electroplating ............................... 333
6.10 Laser Chemical Vapour Deposition ...................... 334
6.11 Laser Physical Vapour Deposition ...................... 335
6.12 Noncontact Bending .................................... 335
6.13 Magnetic Domain Control ............................... 336
6.14 Laser Cleaning and Paint Stripping .................... 337
6.15 Surface Roughening .................................... 337
6.16 Scabbling ............................................. 337
6.17 Micromachining ........................................ 338
6.18 Laser Marking ......................................... 339
6.19 Shock Hardening ....................................... 340
6.20 Conclusions ........................................... 342
References ................................................. 342
7 Rapid Prototyping and Low-volume Manufacture ............... 349
7.1 Introduction .......................................... 349
7.2 Range of Processes .................................... 350
7.2.1 Styles of Manufacture .......................... 350
7.2.2 Classification of Rapid Prototyping
Techniques by Material ......................... 351
7.3 Computer Aided Design File Manipulation ............... 351
7.4 Layered Manufacturing Issues .......................... 353
7.4.1 General ........................................ 353
7.4.2 Stair Stepping ................................. 353
7.4.3 Layer Thickness Selection ...................... 354
7.4.4 Accuracy ....................................... 354
7.4.5 Part Orientation ............................... 354
7.4.6 Support Structures ............................. 354
7.5 Individual Processes .................................. 355
7.5.1 Stereolithography .............................. 355
7.5.2 Selective Laser Sintering ...................... 358
7.5.3 Laminated-object Manufacture ................... 360
7.5.4 Laser Direct Casting or Direct Metal
Deposition (DMD) ............................... 362
7.6 Rapid Manufacturing Technologies ...................... 365
7.6.1 Silicone Rubber Moulding ....................... 365
7.6.2 Investment Casting ............................. 365
7.6.3 Sand Casting ................................... 366
7.6.4 Laser Direct Casting ........................... 366
7.6.5 Rapid Prototyping Tooling ...................... 367
7.7 Applications .......................................... 367
7.8 Conclusions ........................................... 367
References ............................................ 368
8 Laser Ablative Processes - Macro- and Micromachining ....... 371
8.1 Introduction .......................................... 371
8.2 Basic Mechanisms During Short Radiant Interactions .... 372
8.2.1 Thermal Models ................................. 372
8.2.2 Nonthermal Models .............................. 373
8.3 Case 2: Nanosecond Pulse Impact ....................... 375
8.4 Case 3: Ultrashort Pulses ............................. 378
8.5 Applications .......................................... 379
8.3 Low-energy Pulses (Less than 150 nj) .................. 379
8.5.2 Medium-energy Pulses (150-500 nj) .............. 380
8.5.3 High-energy Pulses (More than 500 nj) .......... 380
8.6 Summary ............................................... 385
References ............................................ 386
9 Laser Bending or Forming ................................... 389
9.1 Introduction .......................................... 389
9.2 The Process Mechanisms ................................ 390
9.2.1 The Thermal Gradient Mechanism ................. 390
9.2.2 The Point Source Mechanism ..................... 391
9.2.3 The Buckling Mechanism ......................... 392
9.2.4 The Upsetting Mechanism ........................ 393
9.2.5 Laser-induced Shock Bending .................... 393
9.3 Theoretical Models .................................... 394
9.3.1 Models for the Thermal Gradient Mechanism ...... 395
9.3.2 The Buckling Mechanism Model ................... 400
9.3.3 The Upsetting Mechanism Model .................. 402
9.4 Operating Characteristics ............................. 403
9.4.1 Effect of Power ................................ 404
9.4.2 Effect of Speed - "Line Energy" ................ 404
9.4.3 Effect of Material ............................. 405
9.4.4 Effect of Thickness - Thickening at the Bend ... 406
9.4.5 Effect of Plate Dimensions - Edge Effects ...... 407
9.4.6 Effect of the Number of Passes ................. 407
9.5 Applications .......................................... 409
9.6 Conclusions ........................................... 413
References ............................................ 414
10 Laser Cleaning ............................................. 417
10.1 Introduction .......................................... 417
10.2 Mechanisms of Laser Cleaning .......................... 418
10.2.1 Selective Vaporisation ......................... 419
10.2.2 Spallation ..................................... 423
10.2.3 Transient Surface Heating ...................... 424
10.2.4 Evaporation Pressure ........................... 426
10.2.5 Photon Pressure ................................ 429
10.2.6 Ablation (Bond Breaking) ....................... 430
10.2.7 Dry and Steam Laser Cleaning ................... 430
10.2.8 Angular Laser Cleaning ......................... 433
10.2.9 Laser Shock Cleaning ........................... 434
10.3 An Overview of the Laser Cleaning Process ............. 435
10.4 Practical Applications ................................ 436
References ............................................ 437
11 Biomedical Laser Processes and Equipment ................... 441
11.1 Introduction .......................................... 441
11.2 Interaction of Laser Radiation with Biological
Tissue ................................................ 442
11.2.1 Optical Properties of Biological Tissue ........ 442
11.2.2 Thermal Properties of Tissue ................... 445
11.2.3 Mechanical Properties of Tissue ................ 447
11.2.4 Tissue Heating Effects - Nonablative Heating ... 447
11.2.5 Tissue Heating Effects - Ablation .............. 448
11.2.6 Tissue Heating - Nonlinear Interactions with
a Laser Beam ................................... 450
11.3 Medical Applications of Lasers ........................ 451
11.3.1 Ophthalmology .................................. 451
11.3.2 Surgical Applications .......................... 454
11.4 Medical Diagnostics ................................... 466
11.4.1 Absorption Techniques .......................... 466
11.4.2 Spectral Techniques ............................ 466
11.4.3 Visualisation Techniques ....................... 467
11.5 Laser Manufacture of Medical Devices .................. 470
11.5.1 Laser Cutting .................................. 470
11.5.2 Marking ........................................ 471
11.5.3 Wire Stripping ................................. 471
11.5.4 Laser Welding .................................. 472
11.5.5 Nanomedicine ................................... 473
11.5.6 Scaffolds for Tissue Engineering ............... 476
11.6 Conclusion ............................................ 480
References ............................................ 482
12 Laser Automation and In-process Sensing .................... 485
12.1 Automation Principles ................................. 485
12.2 In-process Monitoring ................................. 488
12.2.1 Monitoring Beam Characteristics ................ 488
12.2.2 Monitoring Worktable Characteristics ........... 496
12.2.3 Monitoring Process Characteristics ............. 499
12.3 In-process Control .................................... 511
12.3.1 In-process Power Control ....................... 511
12.3.2 In-process Temperature Control ................. 512
12.4 "Intelligent" In-process Control ...................... 513
12.5 Conclusions ........................................... 515
References ............................................ 516
13 Laser Safety ............................................... 519
13.1 The Dangers ........................................... 519
13.2 The Standards ......................................... 519
13.3 The Safety Limits ..................................... 520
13.3.1 Damage to the Eye .............................. 520
13.3.2 Damage to the Skin ............................. 522
13.4 Laser Classification .................................. 523
13.5 Typical Class 4 Safety Arrangements .............. 524
13.6 Where Are the Risks in a Properly Set Up
Facility? ........................................ 524
13.7 Electrical Hazards ............................... 525
13.8 Fume Hazards ..................................... 525
13.9 Conclusions ...................................... 525
References ............................................ 526
14 Epilogue ................................................... 529
14.1 Power Intensity ....................................... 530
14.2 Power Transmission .................................... 530
14.3 Power Shaping ......................................... 530
14.4 Automation ............................................ 530
14.5 Beam Coherence ........................................ 531
14.6 Beam Spectral Purity .................................. 531
14.7 Multiphoton Events .................................... 531
14.8 Frequency-related Events .............................. 531
14.9 Equipment Developments ................................ 531
14.10 Unthought-of Concepts ................................ 532
Index ......................................................... 535
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