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Ultra-fast Material Metrology

ISBN: 978-3-527-40887-0
222 pages
October 2009
Ultra-fast Material Metrology (3527408878) cover image

Description

This book is the first to describe novel measurement techniques of processes during laser-matter interaction using ultra-fast lasers. Targeted at both engineers and physicists, initial chapters address the working tools, the history of laser ultra-fast metrology, an overview of ultra-fast laser sources, and the fundamentals of laser radiation-matter interaction. Ultra-fast laser radiation is discussed in chapter 4, while further chapters describe the methodology of pump and probe in practice, as well as applications for pump and probe metrology in engineering, including spectroscopy and imaging techniques. Chapter 7 describes the perspectives for this new field of research and predicts the metrology of the future, showing new potential applications of laser sources and new detectors in combination with improved pump and probe methods.
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Table of Contents

A Personal Foreword VII

Preface to the First Edition XIII

Acknowledgment XV

1 Introduction 1

1.1 Motivation 1

1.2 Definition of Optical Pump and Probe 4

1.3 Guideline 4

1.4 Matrix of Laser Effects and Applications 5

1.5 Historical Survey of Optical Ultra-fast Metrology 6

1.5.1 Metrology Techniques Before the Advent of Laser 6

1.5.2 Ultra-fast Pump and Probe Metrology 7

2 Ultra-fast Engineering Working Tools 11

2.1 Ultra-fast Laser Sources 11

2.1.1 General Aspects for Ultra-precise Engineering 12

2.1.2 General Aspects on Ultra-fast Lasers for Ultra-fast Metrology 13

2.1.3 Laser Oscillator 15

2.1.3.1 Rod and Disk Solid-State Laser 15

2.1.3.2 Fiber Oscillator 16

2.1.4 Amplifier 18

2.1.4.1 Amplification Media 18

2.1.4.2 Chirped-Pulse Amplification (CPA) 18

2.1.4.3 Optical Parametric Chirped-Pulse Amplification (OPCPA) 19

2.1.4.4 Amplifier Designs 20

2.1.4.5 Commercial Systems 24

2.1.5 Facilities 25

2.2 Focusing of Ultra-fast Laser Radiation 26

2.2.1 Ultra-small Laser Focus 26

2.2.2 Gaussian Beam 27

2.2.3 Beam Parameters of Gaussian Radiation 29

2.2.4 Pulse Duration 32

2.2.5 Beam Stability 34

2.2.6 Key Parameters for Ultra-precision Machining and Diagnostics 35

2.2.6.1 Ultra-precise Machining 35

2.2.6.2 Ultra-fast Pump and Probe Diagnostics for Mechanical Engineering 36

2.3 Beam Positioning and Scanning 36

2.3.1 Positioning 37

2.3.2 Scanning Systems 39

2.4 New Challenges to Ultra-fast Metrology 41

2.4.1 Temporal Domain 42

2.4.2 Spatial Domain 42

2.5 Domains of Optical Pump and Probe Techniques for Process Diagnosis 43

3 Fundamentals of Laser Interaction 45

3.1 Linear to Non-linear Optics 45

3.1.1 Linear Optics: Group Velocity Dispersion and Chirp 45

3.1.2 Non-linear Processes 48

3.1.2.1 Non-linear Polarization 48

3.1.2.2 Self-focusing 49

3.1.2.3 Spectral Broadening by Self-phase Modulation 51

3.1.2.4 Catastrophic Self-focusing 53

3.2 High-Power Photon–Matter Interaction 54

3.2.1 Absorption of Laser Radiation inMatter 54

3.2.2 Energy Transfer from Electrons to Matter 56

3.2.3 Melting and Vaporization 58

3.2.4 Melt Dynamics 60

3.2.5 Onset of Ablation 62

3.2.6 Ionization 63

3.3 Matching of Plasma Dynamics on Ultra-fast Time-Scale 64

3.3.1 Absorption of Radiation in a Plasma 64

3.3.1.1 ElectromagneticWaves in Plasmas 64

3.3.1.2 Inverse Bremsstrahlung 66

3.3.2 Plasma Heating 69

3.3.3 Ionization of a Plasma 72

3.3.3.1 Cross-Section and Collision Frequency 73

3.3.4 Electron Transitions and Energy Transport 74

3.3.4.1 The Total Emission 76

3.3.4.2 The Opacity 76

3.3.5 Dielectric Function of a Plasma 77

3.3.6 Ponderomotive Force 78

4 Fundamentals of Pump and Probe 81

4.1 Ultra-fast Laser Radiation 81

4.1.1 Beam Propagation 82

4.1.2 Dispersion 82

4.1.3 Coherence 83

4.2 Preparation of States and Conditions for Probe Beams 85

4.2.1 Preparation of States 86

4.2.2 Preparation of States by Spectro-Temporal Shaping 86

4.2.3 Measurement of States 88

4.2.4 Measurement of Radiation Properties 89

4.2.4.1 Pulse Duration 89

4.2.4.2 Spectral Phase 90

4.3 Imaging with Ultra-fast Laser Radiation 91

4.3.1 Diffraction Theory and Incoherent Illumination 91

4.3.2 Image Formation by Microscopy and Coherent Illumination 95

4.4 Temporal Delaying 97

4.4.1 Mechanical Delay 98

4.4.1.1 Single-Pass Delay Stage 98

4.4.1.2 Multi-Pass Delay Stage 99

4.4.1.3 Mechanical Optoelectronic Scanning 101

4.4.2 Non-mechanical Delay 101

4.4.2.1 Free-Running Lasers 102

4.4.2.2 Synchronized Lasers 103

5 Examples for Ultra-fast Detection Methods 105

5.1 Non-imaging Detection 106

5.1.1 Transient Absorption Spectroscopy (TAS) 106

5.1.1.1 Principle and Setup 106

5.1.1.2 Characterization of the White-Light Continuum 108

5.1.1.3 Measurement by TAS 112

5.1.2 Temporal Shaped Pulses 113

5.1.2.1 Principle and Setup 113

5.1.2.2 Characterization of the Si-Kα-Radiation Source 115

5.2 Imaging Detection 118

5.2.1 Non-coherent Methods 119

5.2.1.1 Shadowgraphy 119

5.2.1.2 Transient Quantitative Phase Microscopy (TQPm) 120

5.2.2 Coherent Methods 124

5.2.2.1 Mach–Zehnder Micro-Interferometry 124

5.2.2.2 Speckle Microscopy 127

5.2.2.3 Nomarsky Microscopy 129

6 Applications of Pump and Probe Metrology 133

6.1 Drilling of Metals 134

6.1.1 Introduction 134

6.1.2 Measurement of Ejected Plasma, Vapor and Melt 134

6.2 Microstructuring of Metals 137

6.2.1 Introduction 137

6.2.2 Detection of Plasma Dynamics 138

6.3 Marking of Glass 140

6.3.1 Introduction 140

6.3.2 Detection of Laser-Induced Defects 141

6.3.3 Detection of Refractive-Index Changes and Cracking 143

6.4 Welding of Technical Glasses and Silicon 145

6.4.1 Introduction 145

6.4.2 Detection of Laser-Induced Melting 146

7 Perspectives for the Future 151

7.1 Laser and Other Sources 152

7.2 Methodology 153

7.2.1 Scanning Technology 153

7.2.1.1 Spatial Scanning 153

7.2.1.2 Temporal Scanning 153

7.2.2 Beam Shaping 153

7.2.2.1 Spatial Shaping 153

7.2.2.2 Temporal Shaping 154

8 Summary 155

Appendix A Lock-in Amplifier 159

Appendix B Onset on Optics 161

B.1 Abbe Sine Condition 161

B.2 Quantitative Phase Microscopy 162

Appendix C Plasma Parameters 165

C.1 Transport Coefficients 165

C.1.1 Electrical Conductivity 165

C.1.2 Thermal Conductivity 165

C.1.3 Diffusivity of Electrons 166

C.1.4 Viscosity 167

C.2 Debye Length 168

C.3 Plasma Oscillations andWaves 169

C.4 Coupling Between Electrons and Ions 171

C.5 Hydrodynamic Instabilities 172

Appendix D Facilities 173

Appendix E List of Abbreviations and Symbols 177

E.1 Abbreviations 177

E.2 Symbols 178

References 183

Glossary 195

Index 199

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Author Information

Alexander Horn has been Senior Scientist at the chair for Laser Technology (LLT) of the RWTH Aachen since 2003, and Group Leader of the Ultrafast-Technology group since 2004. He studied Physics in Siegen, Germany, and graduated in 2003 to Dr. rer. nat. with "suma cum laude". In March 2008 he starts a new position as a representative professor at the Institute for Physics of the University of Kassel (Germany). His main field of research is the ultra-fast detection of laser-induced processes, especially the development & usage of novel pump & probe techniques. He has authored over 40 scientific publications.
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