1 Introduction ................................................. 9
2 Fundamentals of THz time-domain spectroscopy ................ 13
2.1 Generation of THz pulses ............................... 13
2.1.1 Carrier acceleration in the surface field ....... 14
2.1.2 Carrier dynamics in photoconductive switches .... 15
2.1.3 Layout of photoconductive emitters .............. 17
2.1.4 Frequency mixing ................................ 19
2.1.5 Phase matching or the conservation of
momentum ........................................ 22
2.1.6 The angular dependence of the second-order
susceptibility .................................. 25
2.2 Detection of THz pulses ................................ 27
2.2.1 Substrates with short carrier lifetimes ......... 27
2.2.2 Electro-optical sampling ........................ 31
2.3 Essential data analysis in THz Spectroscopy ............ 32
2.4 THz beam propagation ................................... 34
2.4.1 Quasi-Optical Systems ........................... 34
2.4.2 THz wave-guiding ................................ 39
3 Scalable photoconductive THz emitters and detectors ......... 43
3.1 Chip Layout ............................................ 44
3.1.1 Manufacturing ................................... 46
3.2 Scalable antenna as an emitter ......................... 47
3.2.1 Performance and operating parameters ............ 47
3.3 Scalable emitter for excitation wavelengths above
1 μm ................................................... 50
3.3.1 GaInAsN substrate ............................... 50
3.3.2 Experimental .................................... 52
3.3.3 Results and Discussion .......................... 53
3.3.4 Comparison with conventional SI GaAs based
emitter ......................................... 55
3.4 THz detector properties ................................ 57
3.4.1 Ion implanted GaAs .............................. 57
3.4.2 Electrical Characterization ..................... 59
3.4.3 Results and Discussion .......................... 62
3.5 THz beams of radial and azimuthal polarization ......... 67
3.6 Summary and Outlook .................................... 72
3.6.1 Emitter for excitation wavelengths above 1μm .... 72
3.6.2 Scalable photoconductive detector ............... 72
3.6.3 Radially and azimuthally polarized THz
radiation ....................................... 72
4 Examples for Terahertz Time Domain Spectroscopy ............. 75
4.1 Determination of the dielectric function with THz
TDS .................................................... 75
4.2 Examples of THz-TDS in process monitoring and food
inspection ............................................. 77
4.3 Summary and Outlook .................................... 79
5 THz emission by frequency mixing ............................ 83
5.1 Optical rectification with DAST ........................ 83
5.2 Optical rectification with GaAs ........................ 88
5.2.1 Bulk GaAs ....................................... 88
5.2.2 Phasematching in GaAs ........................... 92
5.2.3 GaAs slab ....................................... 94
5.3 Discussion and Summary ................................ 100
A Appendix ................................................... 103
A.l Laser systems ......................................... 103
A.1.1 fs-Titanium-Sapphire-Oscillator ................ 104
A.l.2 kHz Amplifier System ........................... 105
A.1.3 TOPAS .......................................... 107
A.1.4 Optical Parametric Oscillator .................. 108
A.2 Lorentz Oscillator Model .............................. 109
A.3 Publications not explicitly discussed in this
thesis ................................................ 110
Bibliography .................................................. 113
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