Terahertz radiation from indium arsenide, gallium arsenide and indium phosphide emitters at high excitation fluences and applications

In this thesis, terahertz emission from semiconductor surfaces is studied at high optical excitation fluences in order to investigate the scaling of such sources to high efficiencies. A quantitative comparison of terahertz emission from InAs surfaces, one of the more efficient semiconductor sources, to the most efficient reported pulsed terahertz emitter, a large-aperture GaAs photoconductive switch, is carried out. It is found that at high bias voltages the large-aperture photoconductive switch is more efficient at converting optical to far-infrared energy but that the InAs semiconductor source has a higher frequency bandwidth.; In the high excitation fluence regime, it is found that the dominant emission mechanism from InAs surfaces changes from the previously reported photo-carrier dominated processes at low excitation fluences. A detailed calculation of bulk and surface electric field induced optical rectification from zinc blende crystals is performed. The calculations are compared to the experimental observation of optical second-harmonic generation and terahertz emission from InAs surfaces for various crystal orientations. The results indicate that the dominant emission mechanism for terahertz radiation from InAs is surface electric-field induced optical rectification.; A comparison of emission of THz radiation from porous crystalline surfaces of InP versus unstructured surfaces was carried out. It was demonstrated, for the first time, that an increased conversion efficiency of terahertz radiation could be achieved with the introduction of porosity and in particular that the optical rectification component of terahertz emission from InP surfaces could be enhanced with the introduction of porosity. The mechanism for the enhancement is tentatively attributed to local-field enhancement within the porous network.; A terahertz time-domain spectrometer set-up was constructed, employing a semi-large aperture photoconductive switch. This system was characterized and applied to the study of wood and wood products. Specifically, it was demonstrated in a transmission mode that wood samples exhibit both birefringence and diattenuation. These results could lead to potential applications for the determination of fiber orientation in wood products such as the analysis of fiber orientation in paper products.