Landolt-Brnstein GROUP VIII:Advanced Materials and Technologies VOLUME 1 Laser Physics and Applications SUBVOLUME C Laser Applications Title Pages
Contributors, Preface, Contents
Contributors
Preface
Contents
1 Fundamentals 1
1.1 Fundamentals of laser-induced processes (H. HGEL, F. DAUSINGER) 3
1.1.1 Introduction 3
1.1.2 Energy coupling 4
1.1.2.1 Fundamentals 4
1.1.2.2 Optical properties of metals 6
1.1.2.2.1 Temperature effects 9
1.1.2.2.2 Chemical effects 14
1.1.2.2.3 Roughness effects 14
1.1.2.3 Optical properties of ceramics 16
1.1.2.4 Scattering and absorption by particles 18
1.1.2.5 Non-linear absorption 24
1.1.3 Thermophysical and dynamical response 25
1.1.3.1 Condensed matter 25
1.1.3.1.1 Heat conduction 25
1.1.3.1.1.1 Fourier heat conduction 25
1.1.3.1.1.2 Two-temperature model 28
1.1.3.1.2 Phase transitions 30
1.1.3.1.2.1 Melting 30
1.1.3.1.2.2 Evaporation 32
1.1.3.1.3 Melt dynamics 34
1.1.3.1.3.1 Origin of driving forces 34
1.1.3.1.3.2 Resulting effects in laser machining 35
1.1.3.2 Interaction mechanisms in the gas and plasma phase 37
1.1.3.2.1 Basic ionization and absorption mechanisms 38
1.1.3.2.1.1 Bound electrons 38
1.1.3.2.1.2 Free electrons 40
1.1.3.2.2 Absorption and refraction effects in laser-induced plasmas 41
1.1.3.2.2.1 Plasma composition and temperature 41
1.1.3.2.2.2 Absorption 47
1.1.3.2.2.3 Refraction 50
1.1.3.2.3 Dynamical effects 52
1.1.4 Simplified dependences in laser processes	56
1.1.4.1 Energy coupling in laser processes	56
1.1.4.1.1 Coupling rate in laser cutting	56
1.1.4.1.2 Coupling rate in laser welding	57
1.1.4.2 Process windows	58
1.1.4.2.1 Power threshold	59
1.1.4.2.2	Factors determining process velocity 60
1.1.4.2.3 Factors determining efficiency 61
References for 1.1 62
2 Production engineering 73
2.1	Surface treatment (H.W. BERGMANN) 75
2.1.1 Laser macro processing	75
2.1.1.1 Solid-state hardening	76
2.1.1.1.1 Physical basics	76
2.1.1.1.2 Material science basics	77
2.1.1.1.3 Production-related aspects	78
2.1.1.1.4 Time scheme of the irradiation	79
2.1.1.1.5 Observed degradations and their reasons	79
2.1.1.2 Remelting	81
2.1.1.2.1 Remelting of cast iron	83
2.1.1.2.2 Remelting of aluminum alloys	84
2.1.1.2.3 Remelting of titanium alloys	86
2.1.1.2.4 Remelting of magnesium alloys	88
2.1.1.2.5 Observed degradations of surface-remelted components and their reasons	89
2.1.1.3 Laser cladding	92
2.1.2 Thin-layer technologies	95
2.1.2.1 Laser cleaning	96
2.1.2.2 Laser cleaning and smoothing of cast iron	97
2.1.2.3	Surface alloying 97
2.1.3	Laser shock hardening 98
References for 2.1 101
2.2	Rapid prototyping (A. GEBHARDT) 105
2.2.1 Layer manufacturing	106
2.2.1.1 Rapid-prototyping process chain	106
2.2.1.2 Prototypers	107
2.2.1.3 Characteristics of rapid-prototyping processes	108
2.2.1.4 Materials	108
2.2.1.5 Post-processing	113
2.2.1.6 Finishing	113
2.2.1.7 Functional metal parts	113
2.2.1.8 Rapid tooling	113
2.2.1.8.1 Indirect rapid tooling	115
2.2.1.8.2 Direct rapid tooling	116
2.2.2 Application of rapid-prototyping models	117
2.2.2.1 Model characteristics and model properties	117
2.2.2.2 Criteria for the use of rapid-prototyping models	117
2.2.2.3	Examples 119
2.2.2.4	Rapid manufacturing 121
2.2.3	Recent developments and future trends 121
References for 2.2 123
2.3	Thermal bending (M. GEIGER, F. VOLLERTSEN) 125
2.3.1	Principle of laser forming 125
2.3.2	Mechanisms 125
2.3.3	Influence parameters 126
2.3.3.1	Threshold energy 127
2.3.3.2	Processing parameters 127
2.3.3.3	Material parameters 128
2.3.3.4	Geometric parameters 130
2.3.4	Bend radii 131
2.3.5	State of the art and trends 132
References for 2.3 133
2.4	Joining (H. HAFERKAMP) 137
2.4.1	Introduction 137
2.4.2	Conduction welding 139
2.4.3	Deep-penetration welding 140
2.4.3.1	Capillary formation 142
2.4.3.2	Plasma formation 143
2.4.3.3	Humping effect 144
2.4.4	Material weldability 145
2.4.5	Thermal distortion 146
2.4.6	Tailored blanks 147
2.4.7	Soldering and brazing 149
2.4.8	Diode-laser applications 150
2.4.9	How to avoid quality degradation 151
References for 2.4 156
2.5	Laser separating (W. O'NEILL) 159
2.5.1	Introduction 159
2.5.2	Cutting 160
2.5.2.1	Fusion cutting 160
2.5.2.2	Reactive-gas cutting 162
2.5.2.3	Sublimation cutting 163
2.5.3	Cleaning 163
2.5.4	Machining 167
2.5.4.1	Oxidation processes 168
2.5.4.2	Liquid-phase machining 168
2.5.4.3	Vapor-phase machining 168
2.5.5	Drilling 170
2.5.5.1	Piercing 172
2.5.5.2 Multiple-pulse drilling	172
2.5.5.3 Trepanning	173
2.5.5.4 High-speed drilling	175
2.5.6 Non-thermal ablation	176
2.5.7	Marking 177
2.5.8	Comparison with conventional processes 178
2.5.9	How to avoid quality degradation 180
References for 2.5 184
2.6	Cutting: Modeling and data (W. SCHULZ, C. HERTZLER) 187
2.6.1	Diagnostics, monitoring and modeling 188
2.6.2	Experiments and diagnostics 189
2.6.3	Mathematical formulation 191
2.6.4	Inertial manifolds 192
2.6.5	Dimension in phase space 193
2.6.6	Spatial one-dimensional model 194
2.6.7	Spatial two-dimensional model and diffusive eikonal 196
2.6.8	Iterative refinement 199
2.6.9	Cutting data 202
2.6.9.1	Laser power 202
2.6.9.2	Modulation of the laser output (gating frequency) 203
2.6.9.3	Beam quality and power density distribution 203
2.6.9.4	Spatial and temporal beam stability 205
2.6.9.5	Polarization 205
2.6.9.6	Output mirrors of the laser unit 205
2.6.9.7	Beam alignment 205
2.6.9.8	Astigmatism 206
2.6.9.9	Deflection mirror 206
2.6.9.10	Focusing lens 206
2.6.9.11	Beam to nozzle alignment 206
2.6.9.12	Shape of nozzle exit 207
2.6.9.13	Cutting speed 207
2.6.9.14	Type of assist gas 207
2.6.9.15	Gas pressure 207
2.6.9.16	Focal position 208
2.6.9.17	Material type and composition 208
2.6.9.18	Thickness 208
2.6.9.19	Surface condition of the sheet metal 208
2.6.9.20	Cut shape 209
2.6.9.21	Kerf width 209
2.6.9.22	Dross formation 210
2.6.9.23	Mean roughness 210
2.6.9.24	Perpendicularity and slant tolerance 211
2.6.9.25	Drag lines 211
2.6.9.26	Pitting 211
2.6.9.27	Heat-affected zone 211
2.6.10	Machining data tables for cutting 212
References for 2.6 215
2.7	Laser systems for materials processing (G. SEPOLD, M. GRUPP) 219
2.7.1	Laser macro systems 220
2.7.1.1	Laser sources 221
2.7.1.1.1	CO2-laser 221
2.7.1.1.2	Nd:YAG laser 222
2.7.1.1.3	High-power diode lasers 223
2.7.1.1.4	Fiber lasers and thin disc lasers 224
2.7.1.2	Laser beam guiding 224
2.7.1.2.1	Beam-guiding systems for CO2-lasers 224
2.7.1.2.2	Beam guiding for Nd:YAG-lasers 225
2.7.1.3	Beam-forming elements 226
2.7.1.3.1	Focusing optics 227
2.7.1.3.1.1	Laser cutting heads 228
2.7.1.3.1.2	Welding heads 228
2.7.1.3.1.3	Working heads for surface treatment 229
2.7.1.4	Handling devices 230
2.7.1.4.1	System concepts 230
2.7.1.4.1.1	1-dimensional systems 230
2.7.1.4.1.2	2-dimensional systems 230
2.7.1.4.1.3	3-dimensional systems 232
2.7.1.4.2	New developments 234
2.7.1.4.3	Special systems 235
2.7.1.4.4	Actuation and control of laser systems 236
2.7.1.4.5	Clamping devices 236
2.7.2	Laser microtechnology 237
2.7.2.1	Beam sources 238
2.7.2.2	Beam-guiding and -forming techniques 238
2.7.3	Conclusions and outlook 239
References for 2.7 241
2.8	Process monitoring and closed-loop control (W. WIESEMANN) 243
2.8.1	Introduction 243
2.8.2	Basics of process monitoring and closed-loop control 244
2.8.2.1	General 244
2.8.2.2	Process-surveillance objectives and strategies 245
2.8.2.2.1	Support for scientific research by monitoring of process output parameters 245
2.8.2.2.2	On-line treatment fault probability assessment and documentation during serial production 246
2.8.2.2.3	Closed-loop control during serial production 246
2.8.2.3	Treatment quality indicators, span of surveillance 247
2.8.2.4	Process output parameter detection 249
2.8.2.4.1	Theoretical introduction 249
2.8.2.4.2	Radiation emission from the interaction zone 250
2.8.2.4.3	Radiation reflection and transmission at the interaction zone 250
2.8.2.4.4 Radiation detection and sensor arrangement 251
2.8.2.4.5 Two-dimensionally resolved radiation emission 252
2.8.2.4.6 Sound detection 253
2.8.2.4.7 Electrical-charge detection 253
2.8.2.4.8 Multiple-sensor fusion 253
2.8.2.5 Signal assessment methods 254
2.8.2.6 Control actions 256
2.8.3 State of the art of process monitoring and control technology 258
2.8.3.1 Cutting and drilling 259
2.8.3.1.1 General 259
2.8.3.1.2 Scientific research 259
2.8.3.1.2.1 Cutting 259
2.8.3.1.2.2 Drilling, piercing 260
2.8.3.1.3 Industrial applications 261
2.8.3.2 Welding 261
2.8.3.2.1 General and historical 261
2.8.3.2.2 Recent scientific research 262
2.8.3.2.2.1 Optical emissions, photo-diode detection 263
2.8.3.2.2.2 Optical emissions, camera detection 264
2.8.3.2.2.3 Reflected laser radiation 264
2.8.3.2.2.4 Electrical charge collection 265
2.8.3.2.2.5 Multiple sensor schemes 265
2.8.3.2.2.6 X-ray and visible-light shadowgraphy, holography, laser beam probe, ultrasonic inspection 266
2.8.3.2.3 Industrial applications 267
2.8.3.2.3.1 Monitoring systems 267
2.8.3.2.3.2 Closed-loop control systems 268
2.8.3.3 Transformation hardening 268
2.8.3.4 Cladding, alloying 269
2.8.3.5 Cleaning, caving 269
2.8.4 Outlook 270
References for 2.8 272
3 Life science, biological and chemical processing 277
3.1 Lasers in biology and medicine (O. MINET, K. DRSCHEL, G. MLLER) 279
3.1.1 Light and heat transport in tissue 279
3.1.1.1 Light transport and optical parameters 279
3.1.1.2 Heat transport and thermal parameters 282
3.1.2 Laser-tissue interactions 285
3.1.2.1 Laser diagnostics by transillumination and induced fluorescences 285
3.1.2.2 Laser-induced photochemistry 287
3.1.2.3 Photothermal effects 287
3.1.2.3.1 Coagulation 288
3.1.2.3.2 Evaporation of tissue 288
3.1.2.4 Effects of short-pulsed laser radiation 288
3.1.2.4.1 Photoablation 289
3.1.2.4.2 Optical breakdown and plasma formation 290
3.1.2.4.3 Laser-induced shock waves and cavitations	291
3.1.2.5 Laser biostimulation	291
3.1.3 Medical laser systems	292
3.1.3.1 Typical medical lasers	292
3.1.3.2 Laser light delivery	292
3.1.3.2.1 Articulated arm	292
3.1.3.2.2 Light guide	292
3.1.3.2.3 Optical glass fiber	295
3.1.3.2.4 Hollow wave guide	296
3.1.3.3 Applicator systems	296
3.1.4 Laser applications in medicine	296
3.1.5 Medical laser safety	298
3.1.5.1	Medical laser pyrolysis products 298
3.1.5.2	Regulatory requirements for medical laser systems 301
3.1.5.3	Specific aspects of medical laser safety 302
References for 3.1 303
3.2	Laser chemical processing (D. BUERLE) 311
3.2.1	Introduction 311
3.2.2	Pulsed-laser ablation 313
3.2.2.1	Surface patterning 314
3.2.2.2	The threshold fluence 317
3.2.2.3	Ablation rates 317
3.2.2.4	Material damage 319
3.2.2.5	Influence of an ambient atmosphere 320
3.2.2.6	Instabilities, structure formation 320
3.2.3	Materials etching 320
3.2.3.1	Etching of metals 321
3.2.3.2	Etching of semiconductors and insulators 321
3.2.4	Laser-induced chemical vapor deposition (Laser-CVD) 325
3.2.4.1	Microstructures 325
3.2.4.2	Thin-film formation 327
3.2.4.3	Adsorbed layers, hybrid techniques 329
3.2.5	Deposition from liquids 331
3.2.5.1	Electroless plating 332
3.2.5.2	Electrochemical plating 333
3.2.6	Pulsed-laser deposition (PLD) 333
3.2.6.1	Overview of materials and film properties 334
3.2.6.1.1	Inorganic materials 334
3.2.6.1.2	Organic materials 336
3.2.6.2	Nanocrystalline films 338
3.2.6.2.1	Nanocomposite materials 338
3.2.6.2.2	Size-selective ablation 339
3.2.6.3	Hybrid techniques 339
3.2.6.4	Laser-induced forward transfer 339
3.2.7	Chemical surface transformations 339
3.2.7.1 Doping 340
3.2.7.2 Alloying and synthesis 341
3.2.7.3 Oxidation, nitridation, reduction 341
3.2.7.4 Transformation of organic materials, laser lithography 342
References for 3.2 345
4 Optical data processing 353
4.1 Communication (M. MHRLE, H. VENGHAUS) 355
4.1.1 Introduction 355
4.1.2 Heterostructures 356
4.1.3 Material systems 359
4.1.4 Diode laser structures 359
4.1.4.1 Ridge-waveguide (RW) lasers 360
4.1.4.2 Buried-heterostructure (BH) lasers 360
4.1.4.2.1 Conventional BH-lasers 361
4.1.4.2.2 Semi-insulating BH-lasers 362
4.1.4.2.3 Buried-Ridge-Stripe (BRS) lasers 362
4.1.5 Laser types 362
4.1.5.1 Multimode devices (Fabry-Perot (FP) lasers) 362
4.1.5.2 Single-mode devices 364
4.1.5.2.1 Distributed-feedback (DFB) lasers 364
4.1.5.2.2 Distributed-Bragg-reflector (DBR) lasers 367
4.1.6 Characteristics of 1.3 mand 1.5 m lasers 367
4.1.6.1 Fabry-Perot (FP) lasers 368
4.1.6.2 Distributed-feedback (DFB) lasers 371
4.1.6.2.1 General 371
4.1.6.2.2 Linewidth 373
4.1.6.2.3 HF characteristics 373
4.1.6.3 Lasers for uncooled operation 374
4.1.6.4 Lasers for supervisory channels 375
4.1.7 Fiber-based lasers 375
4.1.7.1 Fiber lasers 375
4.1.7.2 Hybrid Fabry-Perot fiber Bragg grating lasers 376
4.1.8 Integrated laser-modulator 376
4.1.9 Tunable lasers 378
4.1.9.1 Standard devices 378
4.1.9.2 Semiconductor lasers with enhanced tuning range 379
4.1.9.3 Commercial tunable single-chip (SC) lasers 380
4.1.9.4 Linewidth of widely tunable lasers 380
4.1.9.5 Wavelength tunable/selectable fiber laser 380
4.1.9.6 External-cavity laser 381
4.1.10 Monolithic integrations 381
4.1.10.1 Integrated spot size converter 381
4.1.10.2 Integrated multi-wavelength sources 382
4.1.10.3 Integrated mm-wave source 383
4.1.10.4 Transceiver 384
4.1.11 Lasers for advanced optical systems 384
4.1.11.1 Short-pulse sources 384
4.1.11.2 Self-pulsating lasers 384
4.1.12 Pump lasers for optical amplification 385
4.1.12.1 Pump lasers for erbium-doped fiber amplifiers (EDFAs) 385
4.1.12.2 Pump lasers for Raman amplification 386
4.1.13 Vertical-cavity surface-emitting lasers (VCSELs) 386
4.1.13.1 Short-wavelength VCSELs 387
4.1.13.2 Long-wavelength (1.3 m, 1.55 m) VCSELs 388
4.1.13.2.1 1.3 mVCSELs 389
4.1.13.2.2 1.55 mVCSELs 389
4.1.13.3 Tunable VCSELs 392
4.1.14 Reliability 392
References for 4.1 395
5 Metrology 403
5.1 High-precision optical metrology for surfaces (H.J. TIZIANI, M. TOTZECK) 405
5.1.1 Introduction 405
5.1.2 Microstructure metrology 407
5.1.2.1 Resolution in optical imaging 407
5.1.2.2 Improving the optical resolution 410
5.1.2.2.1 Decreasing the wavelength 410
5.1.2.2.2 Increasing the numerical aperture (NA) 411
5.1.2.2.3 Decreasing the prefactor .411
5.1.2.3 Usage of a-priori information: From model-based imaging to threshold criteria 411
5.1.3 Methods and instrumentation 412
5.1.3.1 High-NA lenses 413
5.1.3.2 Field-measuring microscopy 414
5.1.3.2.1 Intensity microscopy 414
5.1.3.2.2 Microscopy with pupil filters 417
5.1.3.2.3 Interference microscopy 417
5.1.3.2.4 Polarization interferometry 420
5.1.3.3 Confocal microscopy 421
5.1.3.4 Near-field microscopy 425
5.1.4 Large-field metrology 428
5.1.4.1 Interferometry for spherical surfaces 428
5.1.4.2 Aspherics and their testing methods 429
5.1.4.3 Interferometry for aspherical surfaces 429
5.1.4.3.1 The computer-generated hologram (CGH) null 429
5.1.4.3.2 Computation and fabrication of CGHs 431
5.1.4.3.3 CGH application and error reduction 432
5.1.4.4 Heterodyne interferometry 433
5.1.4.4.1 Principle of external reference 433
5.1.4.4.2 Scanning differential heterodyne interferometry 435
5.1.4.5 Shack-Hartmann sensors 437
5.1.5 A look into the future 438
References for 5.1	439
5.2	Environmental control (M. ULBRICHT) 443
5.2.1	Introduction 443
5.2.2	Tunable diode laser spectroscopy (TDLAS) 443
5.2.3	Cavity ring-down spectroscopy (CRDS) 444
5.2.4	Photoacoustic spectroscopy (PAS) 445
5.2.5	Lidar 446
5.2.5.1	Backscatter lidar 446
5.2.5.2	Differential absorption lidar (DIAL) 447
5.2.5.3	Raman lidar 450
5.2.5.4	Fluorescence lidar 451
5.2.5.5	Doppler lidar 451
5.2.5.6 Lidar using intense femtosecond laser pulses 452
References for 5.2 453
6 Laser safety and ecology 457
6.1	Laser safety (H. WELLING) 459
6.1.1	Hazard potentials 459
6.1.2	Norms and standards for laser safety 460
6.1.3	Effects of laser radiation and safety measures 461
6.1.3.1	Effects of laser radiation on biological tissue 461
6.1.3.2	Threshold limit values and laser classification 464
6.1.3.3	Safety measures 465
6.1.3.4	Hazard distances 465
6.1.3.4.1	Specular-reflected beam 466
6.1.3.4.2	Diffuse-reflected beam 466
6.1.4	Secondary hazard potentials and safety measures 466
6.1.4.1	Laser system and components 466
6.1.4.1.1	Electrical safety 466
6.1.4.1.2	Optical components 467
6.1.4.1.3	Laser gases 467
6.1.4.1.4	Handling devices 468
6.1.4.2	Secondary radiation 468
6.1.4.3	Explosive atmospheres and fire hazards 469
6.1.4.4	Emission of gases and fumes 469
6.1.4.4.1	Characteristics of laser-generated air contaminants 469
6.1.4.4.2	Extraction systems 473
6.1.4.4.3	Filtration 474
6.1.5	Risk assessment 475
6.1.6	Training and education 476
References for 6.1 477
Index 481

