Ultrafast photonic applications for terahertz waveform generation

This thesis presents theoretical and experimental work on the generation of both terahertz (THz) electrical waveforms and free-space THz radiation. Transmission-line-coupled THz electrical waveform generation is introduced first, through the concepts of photoconductive (PC) self-switching and PC frozen wave generation. The PC self-switching technique is demonstrated in both microstrip and coplanar experimental geometries. Here, it is found that electrical pulses as short as 1.2 ps can be generated with a microstrip ultrathin silicon (Si) PC switch, and electrical pulses as short as 2 ps can be generated with a coplanar gallium arsenide (GaAs) PC switch. These results demonstrate a significant increase in the PC switching speed of conventional Si and GaAs devices. In addition to this work, the concept of PC frozen wave generation is introduced as an attractive source for THz electrical waveforms. This technique makes use of a direct-current (DC) to radio-frequency (RF) conversion process that maps the spatial extent of the bias electrode structure onto the temporal shape of the electrical transient. By employing sufficiently short electrode spacings, it is shown that the operation of the device can be extended into the THz frequency-domain.; The concept of PC switching is applied next to the generation of free-space THz radiation. To start, the operational capabilities of a conventional GaAs PC THz emitter are analyzed. It is determined that the operation of the GaAs emitter is limited by both space-charge and near-field THz screening under high optical pump fluences. To overcome these limitations, the ZnSe PC THz emitter is introduced next. The ZnSe PC device offers a substantially higher dielectric breakdown strength (compared to semi-insulating GaAs) and can, therefore, be scaled to extremely large THz powers by increasing the external bias field. Finally, crystalline and polycrystalline ZnSe samples are applied to the detection of free-space THz radiation. It is found that both the crystalline and polycrystalline samples are effective detectors of free-space THz waveforms.