Laser-based Mid-infrared Sources and Applications

About the Author xi

Preface xiii

1 Mid-IR Spectral Range 1

1.1 Definition of the Mid-IR 1

1.2 The World's Second Laser 3

1.3 Internal Vibrations of Molecules 4

References 5

2 Solid-state Crystalline Mid-IR Lasers 7

2.1 Rare-Earth-based Tm3+, Ho3+, and Er3+ Lasers 7

2.1.1 Tm3+ Lasers 7

2.1.2 Ho3+ Lasers 10

2.1.3 Er3+ Lasers 13

2.2 Transition Metal Cr2+ and Fe2+ Lasers 18

2.2.1 Spectroscopic Properties of Cr2+ and Fe2+ 18

2.2.2 Lasers Based on Chalcogenide Crystals Doped with Cr2+ 21

2.2.2.1 Broadly Tunable Cr2+ Lasers 21

2.2.2.2 High-power Continuous-wave Cr2+ Lasers 23

2.2.2.3 High-power Cr2+ CW Laser Systems Operating at 2.94 ?m 23

2.2.2.4 Gain-switched High-power Cr2+ Lasers 24

2.2.2.5 Microchip Cr2+ Lasers 25

2.2.2.6 Waveguide and Thin-disk Cr:ZnSe Lasers 26

2.2.2.7 Mode-locked Cr:ZnS/Cr:ZnSe Lasers 27

2.2.3 Lasers Based on Chalcogenide Crystals Doped with Fe2+ 30

2.2.3.1 Free-running Pulsed Fe:ZnSe/ZnS Lasers 30

2.2.3.2 Gain-switched Regime of Fe2+ Lasers at Room Temperature 32

2.2.3.3 Continuous-wave Fe2+ Lasers 33

2.2.3.4 Tunable Fe2+ Lasers at Room Temperature 35

2.2.3.5 Ultrafast Amplifier in the 3.8-4.8 ?m Range 35

2.3 Summary 35

References 36

3 Fiber Mid-IR Lasers 43

3.1 Introduction 43

3.2 Continuous-wave Mid-IR Fiber Lasers 44

3.2.1 Tm-based Fiber Lasers 44

3.2.2 Ho-based Fiber Lasers 47

3.2.3 Er-based Fiber Lasers 49

3.2.4 Dy-based Fiber Lasers 52

3.2.5 Raman Fiber Lasers 52

3.3 Q-switched Mid-IR Fiber Lasers 54

3.4 Mode-locked Mid-IR Fiber Lasers 56

3.5 Summary 60

References 61

4 Semiconductor Lasers 65

4.1 Heterojunction Mid-IR Lasers 65

4.1.1 GaSb-based Diode Lasers 66

4.1.2 Distributed Feedback GaSb-based Lasers 70

4.2 Quantum Cascade Lasers 73

4.2.1 High Power and High Efficiency QCLs 76

4.2.2 Single-mode Distributed Feedback (DFB) QCLs 79

4.2.3 Broadly Tunable QCLs with an External Cavity 82

4.2.4 Short-wavelength (<4 ?m) QCLs 85

4.2.5 QCLs at Long (16-21 ?m) Wavelengths 86

4.3 Interband Cascade Lasers 87

4.4 Optically Pumped Semiconductor Disk Lasers (OPSDLs) 94

4.4.1 (AlGaIn)(AsSb)-based OPSDL at ? ? 2.3 ?m 95

4.4.2 PbS-based OPSDL at ? = 2.6-3 ?m 96

4.4.3 PbSe-based OPSDL at ? = 4.2-4.8 ?m 96

4.4.4 PbTe-based OPSDL at ? = 4.7-5.6 ?m 98

4.5 Summary 100

References 100

5 Mid-IR by Nonlinear Optical Frequency Conversion 109

5.1 Two Approaches to Frequency Downconversion Using Second-order Nonlinearity 109

5.1.1 Difference Frequency Generation 111

5.1.2 Optical Parametric Oscillators (OPOs) 112

5.1.3 Brief Review of ?(2) Nonlinear Crystals for Mid-IR 115

5.1.3.1 Periodically Poled Oxides 116

5.1.3.2 Birefringent Crystals 116

5.1.3.3 Emerging QPM Nonlinear Optical Materials 119

5.2 Continuous-wave (CW) Regime 121

5.2.1 DFG of CW Radiation 121

5.2.2 CW OPOs 123

5.3 Pulsed Regime 130

5.3.1 Pulsed DFG 130

5.3.2 Pulsed OPOs 133

5.3.2.1 Broadly Tunable Pulsed OPOs 133

5.3.2.2 Narrow-linewidth Pulsed OPOs 143

5.3.2.3 High Average Power OPOs 147

5.3.2.4 High Pulse Energy OPOs 150

5.3.2.5 Waveguide OPOs 152

5.4 Regime of Ultrashort (ps and fs) Pulses 153

5.4.1 Ultrafast DFG 153

5.4.2 Intra-pulse DFG (Optical Rectification) 157

5.4.3 Ultrafast OPOs 161

5.4.3.1 Picosecond Mode 161

5.4.3.2 Femtosecond Mode 163

5.4.4 Ultrafast OPGs 165

5.4.5 Ultrafast OPAs 167

5.5 Raman Frequency Converters 168

5.5.1 Crystalline Raman Converters 169

5.5.2 Fiber Raman Converters 169

5.5.3 Silicon Raman Converters 170

5.5.4 Diamond Raman Converters 171

5.5.5 Other Raman Converters 172

5.6 Summary 174

References 174

6 Supercontinuum and Frequency Comb Sources 189

6.1 Supercontinuum Sources 189

6.1.1 SC from Lead-silicate Glass Fibers 191

6.1.2 SC from Tellurite Glass Fibers 192

6.1.3 SC from ZBLAN Fibers 194

6.1.4 SC from Chalcogenide Glass Fibers 196

6.1.5 SC from Waveguides 203

6.1.6 SC from Bulk Crystals 207

6.1.7 Other SC Sources 212

6.2 Frequency Comb Sources 213

6.2.1 Direct Comb Sources from Mode-locked Lasers 214

6.2.2 Combs Produced by Spectral Broadening in NL Fibers and Waveguides 215

6.2.3 Combs Produced by Difference Frequency Generation 217

6.2.4 OPO-based Combs 220

6.2.5 Combs Based on Optical Subharmonic Generation 226

6.2.6 Microresonator-based Kerr Combs 229

6.2.7 Combs from Quantum Cascade Lasers 234

6.2.8 Combs from Interband Cascade Lasers 235

6.3 Summary 235

References 236

7 Mid-IR Applications 247

7.1 Spectroscopic Sensing and Imaging 247

7.1.1 QCLs for Spectroscopy and Trace-gas Analysis 248

7.1.2 Spectroscopy with ICLs 252

7.1.3 Spectroscopy with DFG and OPO Sources 252

7.1.4 Broadband Spectroscopy with Frequency Combs 253

7.1.5 Hyperspectral Imaging 255

7.2 Medical Applications 258

7.2.1 Laser Tissue Interactions 258

7.2.1.1 Holmium and Thulium Surgical Lasers 258

7.2.1.2 Er:YAG Lasers (? = 2.9 ?m) 259

7.2.1.3 Importance of the Spectral Band of 6-7 ?m 260

7.2.2 Medical Breath Analysis 261

7.2.2.1 Ethane (C2H6) 262

7.2.2.2 NO 262

7.2.2.3 NH3 263

7.2.2.4 CO 263

7.2.2.5 OCS 263

7.2.2.6 Optical Frequency Comb Spectroscopy for Breath Analysis 264

7.3 Nano-IR Imaging and Chemical Mapping 265

7.4 Plasmonics in the Mid-IR 267

7.5 Infrared Countermeasures 269

7.6 Extreme Nonlinear Optics and Attosecond Science 270

7.7 Other Applications 273

7.7.1 Laser Wake-field Accelerators 273

7.7.2 Laser Acceleration in Dielectric Structures 274

7.7.3 Free-space Communications 274

7.7.4 Organic Material Processing 275

References 276

Index 287

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• A tecnologia laser e holografia

Lasers; coherent light; mid-infrared spectral region; laser photonics; ion-doped solid-state lasers; fiber lasers; semiconductor lasers; intrasubband cascade lasers; intersubband cascade lasers; nonlinear optical parametric devices; supercontinuumn and frequency combs generation; spectroscopy; ultrasensitive molecular detection; high-field physics and attophysics