Introduction
Daniel R.Grischkowsky and Daniel Mittleman ................... 1
Spectroscopy in the Terahertz Spectral Region
Frank С.De Lucia ............................................ 39
1. Introduction ................................................ 39
1.1. Radiation and Matter ................................... 40
1.2. What Phenomena Fall in this Energy Range? .............. 40
1.3. Gases .................................................. 41
1.4. Liquids and Solids ..................................... 43
1.5. Applications and Impact of Terahertz Spectroscopy ...... 43
2. Theoretical Underpinnings ................................... 45
2.1. Absorption Strengths ................................... 45
2.2. Energy Levels and Transitions Frequencies .............. 47
2.3. The Character of Rotational Spectra .................... 47
2.4. Rotation-Vibration Spectra ............................. 49
3. Spectroscopic Techniques and Results ........................ 51
3.1. Harmonic Generation .................................... 53
3.2. Sources Based on Mixing of Optical Sources ............. 61
3.3. Tunable Sideband Sources ............................... 65
3.4. Electron Beam Sources .................................. 68
3.5. Femtosecond Sources .................................... 73
4. Applications ................................................ 76
4.1. Atmospheric Spectroscopy ............................... 76
4.1.1. Microwave-Like Instruments ...................... 78
4.1.2. Infrared-Like Instruments ....................... 85
4.2. Astronomical Spectroscopy .............................. 87
4.2.1. Some Telescope Facilities ....................... 90
4.2.2. Two Representative THz Telescopes ............... 90
4.2.3. Examples of Other Results ....................... 99
Acknowledgments ................................ 107
References .................................................... 107
Terahertz Imaging
Daniel Mittlcman ........................................... 117
1. Introduction ............................................... 117
2. Key Components of a THz Imaging System ..................... 118
2.1. The Femtosecond Laser Source .......................... 119
2.2. Optical Delay Line .................................... 119
2.3. Terahertz Optoelectronic Switches ..................... 120
2.4. Terahertz Beam Optics ................................. 123
2.5. Polarization of the THz Beam .......................... 128
2.6. Signal Acquisition .................................... 129
2.7. Data Processing ....................................... 130
3. Imaging with THz-TDS ....................................... 131
3.1. Amplitude and Phase Imaging ........................... 132
3.2. Terahertz Imaging of Liquid Water ..................... 137
3.3. Processing for Amplitude and Phase Imaging ............ 139
3.4. Reflection Imaging .................................... 139
3.5. Burn Diagnostics ...................................... 141
3.6. Terahertz Tomography: The Third Dimension ............. 143
3.7. Interferometric Tomography ............................ 145
4. Future Prospects ........................................... 149
References .................................................... 149
Free-Space Electro-Optic Techniques
Zhiping Jiang and Xi-Cheng Zhang ........................... 155
1. Introduction ............................................... 155
2. Generation ................................................. 155
3. Detection .................................................. 159
3.1. Measurement Principle ................................. 161
3.2. Measurement of Coherent Mid-Infrared Fields ........... 165
3.3. Parallel Measurement: Chirped-Pulse Measurement ....... 165
3.4. Parallel Measurement: Terahertz Streak Camera ......... 168
3.5. Parallel Measurement: 2D Imaging ...................... 171
3.6. Near-Field Terahertz Imaging .......................... 174
3.7. Detection Geometry and Working Conditions ............. 175
3.8. Comparison Between Photoconductive Sampling
and EO Sampling ....................................... 177
3.9. EO Sampling for Continuous-Wave Terahertz Beams ....... 178
4. Applications ............................................... 178
4.1. Dynamics of Interaction of Lattice with Infrared
Photons ............................................... 178
4.2. Spatiotemporal Coupling of Few-Cycle Pulses ........... 180
4.3. Point Scanning Terahertz Imaging ...................... 182
4.4. Electro-Optic Terahertz Transceiver ................... 185
4.5. Compact System ........................................ 186
References .................................................... 187
Photomixers for Continuous-Wave Terahertz Radiation
Scan M.Duffy, Simon Verghese and K.Alex Mcintosh ........... 193
1. Introduction ............................................... 193
1.1. Demonstrated CW Technology for Terahertz Generation ... 194
2. Photomixers: Principle of Operation ........................ 194
2.1. Overview of Operation ................................. 195
2.2. Lifetime of Carriers .................................. 198
2.2.1. Lifetime Modified by Electric Field Profile .... 201
2.3. External Quantum Efficiency ........................... 202
2.4. Thermal Limits ........................................ 205
2.4.1. Improved Thermal Designs: Thin LTG GaAs on AlAs 207
2.4.2. Improved Thermal Designs: Optically Resonant
Cavity (DBR) ................................... 208
2.5. Trade-offs for Enhanced Output Power .................. 209
2.6. Proven High-Power Methods ............................. 211
3. Planar Antennas and Circuitry .............................. 213
3.1. Electrode Capacitance ................................. 213
3.2. Log-Spiral ............................................ 215
3.3. Single Full-Wave Dipoles .............................. 215
3.4. Dual-Antenna Elements ................................. 216
3.4.1. Dual-Dipole Elements ........................... 216
3.4.2. Graphical Design Procedure ..................... 218
3.4.3. Dual-Slot Elements ............................. 220
3.5. Distributed Photomixers ............................... 221
4. Hyperhemisphere Lens ....................................... 222
5. Photomixer Design and Examples ............................. 224
5.1. Dual-Dipole Results ................................... 224
5.2. Practical Measurement Issues and Power Calibration
Difficulties .......................................... 226
5.3. Maximum Power Limitations ............................. 227
6. Applications ............................................... 230
6.1. Local Oscillators ..................................... 230
6.2. Transceivers .......................................... 230
Acknowledgments ............................................ 233
References ................................................. 233
Applications of Optically Generated Terahertz Pulses
to Time Domain Ranging and Scattering
R.Alan Cheville, Matthew T.Reiten, Roger McGowan,
and Daniel R.Grischkowsky .................................. 237
1. Introduction .............................................. 237
1.1. Perspective ........................................... 237
1.2. Theory ................................................ 238
1.3. Measurements .......................................... 241
1.4. Outline ............................................... 244
2. Experiment ................................................. 244
2.1. Overview of Experimental Configurations ............... 244
2.2. Generation and Detection
of Terahertz Electromagnetic Transients ............... 246
2.3. Terahertz Beam Optics for Target Illumination ......... 251
2.4. Targets ............................................... 254
2.5. Scattered Radiation ................................... 255
2.6. Bistatic Range ........................................ 250
3. Theory ..................................................... 257
3.1. Scaling of Maxwell's Equations
in Terahertz Impulse Ranging ............................... 258
3.2. Transfer Function Description of Terahertz
Impulse Ranging System ................................ 259
3.3. Calculation in Time and Frequency ..................... 262
3.4. Calculation of Scattering Coefficients ................ 264
3.4.1. Cylinders ...................................... 264
3.4.2. Spheres ........................................ 265
4. Measurements ............................................... 267
4.1. Conducting and Dielectric Cylinders ................... 267
4.2. Dielectric Spheres .................................... 272
4.3. Data Analysis and the Geometrical Optics Model ........ 273
4.4. Angularly Resolved Scattering Measurements ............ 281
4.5. Gouy Phase Shift ...................................... 285
4.6. Realistic Targets ..................................... 287
5. Summary and Future Directions .............................. 289
References ................................................. 290
Bio-medical Applications of THz Imaging
Martin Koch ................................................ 295
1. Introduction ............................................... 295
1.1. Some General Remarks Regarding Biomedical Imaging ..... 295
1.2. The Closure of the Terahertz Gap ...................... 297
2. Description of the Terahertz Imaging Setup ................. 298
3. Dendrochronology: Density Mapping of Wood .................. 300
4. Plant Physiology: Monitoring the Water Flow in Plants ...... 303
4.1. Clematis .............................................. 305
4.2. Mimosa ................................................ 307
5. Medical Imaging on Histopathological Samples ............... 308
5.1. Time-Domain Imaging ................................... 309
5.2. Continuous-Wave Imaging ............................... 311
6. Conclusion ................................................. 312
Acknowledgments ............................................... 312
References .................................................... 313
Electronic Sources and Detectors for Wideband Sensing
in the Terahertz Regime
Daniel W. van der Weide .................................... 317
1. Introduction ............................................... 317
2. Dual-Source Interferometer ................................. 320
3. Description of DSI ......................................... 321
4. Analysis of Dual-Source Interferometer ..................... 322
5. DSI Results from Dual-Source Interferometer ................ 324
6. Reflection Spectroscopy .................................... 325
7. Coherent Signal Generation with Scanned Delay Lines ........ 328
8. Conclusions ................................................ 331
Acknowledgments ............................................... 331
References .................................................... 331
Index ......................................................... 335 |
