Photorefractive Organic Materials and Applications (eBook)

Preface 6
Contents 8
Contributors 10
Chapter 1: Introduction to the Photorefractive Effect in Polymers 12
1.1 Mathematical Model 15
1.1.1 Charge Generation 15
1.1.2 Charge Transport and Trapping 17
1.1.3 Space-Charge Field 21
1.1.4 Index Modulation 23
1.1.4.1 Electro-Optic Effect 24
1.1.4.2 Orientational Birefringence 26
1.1.5 Diffraction Efficiency 27
1.2 Components 28
1.2.1 Polymer Matrices 29
1.2.2 Chromophores 35
1.2.3 Sensitizers 37
1.2.4 Plasticizers 42
1.3 Devices and Geometries 43
1.4 Characterization 48
1.4.1 Energy Levels 49
1.4.2 Photogeneration Efficiency 50
1.4.2.1 Xerographic Discharge 51
1.4.2.2 DC Photocurrent 51
1.4.3 Mobility 52
1.4.3.1 Time of Flight 52
1.4.3.2 Holographic Time of Flight 53
1.4.3.3 Photoconductivity Dynamics 54
1.4.4 Electro-Induced Refractive Index Change 56
1.4.4.1 Interferometry 56
AC Field 56
1.4.4.2 Ellipsometry 57
1.4.4.3 Electric Field Induced Second Harmonic Generation 57
1.4.5 Two-Beam Coupling 59
1.4.6 Four-Wave Mixing 63
1.5 Conclusion 66
References 67
Chapter 2: Charge Transport and Photogeneration in Organic Semiconductors: Photorefractives and Beyond 75
2.1 Introduction 75
2.2 Basic Properties of Organic Semiconductors 78
2.2.1 Organic Molecules 78
2.2.2 Organic Solids 80
2.3 Charge Transport and Photogeneration in Organic Semiconductors 81
2.3.1 Semiconductors in Thermodynamic Equilibrium 82
2.3.1.1 Electronic Structure 82
2.3.1.2 Electronic Occupation 84
2.3.2 Intrinsic Semiconductors 86
2.3.3 Extrinsic Semiconductors 87
2.3.3.1 Doping of Organic Semiconductors 87
2.3.4 Semiconductors in Non-equilibrium: Charge Transport Models 88
2.3.4.1 Quasi-Fermi Levels 89
2.3.4.2 Drift-Diffusion Model 89
2.3.4.3 Conductivity 91
2.3.4.4 Equations of State 92
2.3.5 Charge Transport in Organic Semiconductors 92
2.3.5.1 Electronic Coupling 92
2.3.5.2 Electron-Phonon Coupling 93
2.3.5.3 Polaron Model: The Holstein Model 93
2.3.5.4 Disorder Models 95
2.3.6 Hopping Rate: Miller-Abrahams Model 95
2.3.7 Hopping Rate: Marcus Model 96
2.3.8 Poole-Frenkel Models 96
2.3.9 Gaussian Disorder Model 97
2.3.9.1 Influence of Randomly Oriented Dipoles 97
2.4 Correlated Gaussian Disorder Model (CGDM): Energy Site Correlations 98
2.5 Effective Medium Model: Polaron and Disorder Effects 99
2.6 Extended Gaussian Disorder Model: Carrier Concentration Dependence 99
2.7 Guest-Host Material Systems 101
2.7.1 Photoconductivity in Organic Materials 101
2.7.1.1 Approximations in the Context of Photorefractive Materials 104
2.7.1.2 Exciton Dissociation 104
2.7.1.3 Photogeneration in Intrinsic Photoconductors: Onsager Model 105
2.7.1.4 Photogeneration in Extrinsic Photoconductors 106
2.7.1.5 Empirical Approximations 107
2.8 Recombination 108
2.8.1 Langevin Recombination Theory 108
2.8.1.1 Spatial Fluctuation in a Potential Landscape 110
2.8.1.2 Trap-Assisted Recombination 110
2.8.1.3 Multiple Trapping-Detrapping 111
2.9 Photoconductivity and Space-Charge Field Formation in Photorefractive Polymers 111
2.9.1 Space-Charge Field: Steady-State 111
2.9.1.1 Space-Charge Field: Temporal Evolution 114
2.10 Materials 116
2.10.1 Extrinsic Photoconductors 117
2.10.1.1 Sensitizers and Charge-Transfer Complexes 118
2.10.1.2 Photoconductors for Photorefractive Applications I: Organic Sensitizers 119
2.10.1.3 Photoconductors for Photorefractive Applications II: Inorganic Sensitizers 122
2.10.2 Small-Molecule Semiconductors: Semicrystalline Materials and Molecular Glasses 124
2.10.3 Donor-Acceptor Polymers 125
References 127
Chapter 3: Photorefractive Response: An Approach from the Photoconductive Properties 138
3.1 Introduction 138
3.2 Photoconduction 140
3.2.1 Photocurrent Dynamics 141
3.2.2 Photorefractive Response and Photoconductivity 145
3.3 The Onsager Model 151
3.4 Carrier Transport 153
3.5 Measurements Methods 156
3.5.1 Xerographic Discharge Method for Carrier Photogeneration [62, 63] 156
3.5.1.1 Emission Limited Discharge Mode (ELD Mode) 158
3.5.1.2 Space-Charge Limited Discharge Mode (SCLD Mode) 159
3.5.2 A Time-of-Flight (TOF) Technique for Drift Mobility [64, 67, 68] 159
3.5.2.1 Current Mode 160
3.5.2.2 Voltage Mode 162
3.6 Molecular and Device Engineering for Fast Response Photorefractive Polymer Composites 162
3.7 Conclusion and Outlook 163
References 163
Chapter 4: Photorefractive Properties of Polymer Composites Based on Carbon Nanotubes 166
4.1 Introduction 166
4.2 Experimental 168
4.3 Results and Discussion 170
4.3.1 Photoelectric Properties 170
4.3.2 Drift Mobility of Charge Carriers 173
4.3.3 Third-Order Nonlinear Optical Properties 176
4.3.4 Photorefractive Characteristics 180
4.3.4.1 Photorefractive Effect at 1550nm 182
4.3.4.2 Photorefractive Effect at 1064nm 185
4.4 Conclusion 192
References 193
Chapter 5: Photorefractive Smectic Mesophases 196
5.1 Introduction 196
5.2 Thermotropic Mesophases: Orientational Order and Properties 198
5.2.1 The Nematic Phase 199
5.2.2 The Smectic A and C Phases 201
5.2.3 Polymer Dispersed Liquid Crystals 206
5.3 Photorefractivity in Chiral Smectic A Phases 207
5.4 Photorefractivity in Chiral Smectic C Phases 211
5.4.1 Initial Investigations 213
5.4.2 Early Developments 214
5.4.3 The Importance of Sample Orientation and Light Polarization 216
5.4.4 Further Studies 220
5.4.5 Bistable SmC* Devices 222
5.5 Conclusions 228
References 229
Chapter 6: Inorganic-Organic Photorefractive Hybrids 232
6.1 Introduction 232
6.2 Inorganic-Organic Photorefractive Hybrids 234
6.3 Conditions for Bragg-Matched Beam Coupling 236
6.4 Methods to Improve Bragg-Matched Photorefractive Beam Coupling 243
6.4.1 Cholesteric Liquid Crystal Photorefractive Hybrid Devices 243
6.4.2 Ferroelectric Nanoparticle Doped Liquid Crystals for Photorefractive Hybrid Devices 245
6.4.2.1 Understanding the Properties of Stressed Ferroelectric Nanoparticles 245
6.4.2.2 Incorporation of Ferroelectric Nanoparticles in Inorganic-Organic Photorefractive Hybrid Devices 250
6.5 Conclusions 253
References 254
Chapter 7: Wave Mixing in Photorefractive Polymers: Modeling and Selected Applications 257
7.1 Introduction 257
7.2 Induced Refractive Index in Steady State 259
7.3 Wave Mixing in the Steady State: Transmission Geometry 263
7.3.1 Steady State Theory 263
7.3.2 Competition Between Gain and Beam Fanning in PR Polymer 267
7.3.3 Other Effects: Gain vs. Incident Intensity, Higher Order Generation 270
7.4 Selected Applications of Wave Mixing 272
7.4.1 Real-Time Edge Enhancement 272
7.4.2 Real-Time Edge-Enhanced Correlation 275
7.4.3 Adaptive Filtering Using Four-Wave Mixing 279
7.5 Transient Two-Wave Mixing: Role of Competing Charge Carriers 280
7.6 Conclusions 285
7.7 Epilogue and Acknowledgments 286
References 287
Chapter 8: Photorefractives for Holographic Interferometry and Nondestructive Testing 290
8.1 Introduction 290
8.2 Techniques for Holographic Metrology 291
8.3 Considerations for Applicability of Holographic Metrology 294
8.3.1 The Ideal Holographic Measurement Device 294
8.3.2 Computation of Phase and Interpretation 296
8.4 Photorefractive Materials for Holographic Interferometry 298
8.4.1 Figures of Merit of Interest 298
8.4.2 Photorefractive Materials Configurations of Interest 300
8.5 Experiments and Industrial System with PR Materials for Nondestructive Testing 302
8.5.1 Laboratory Experiments 302
8.5.2 Compact Holographic Camera Based on Sillenite Crystal and Its Applications 307
8.6 Discussion: Potential of Organic PR Materials 314
8.7 Conclusions 315
References 316
Index 320