High power THz generation in a gallium phosphide waveguide and THz carrier dynamics in epitaxial graphene

The generation and detection of ultrafast time domain (TD) THz pulse trains is an active area of research, with recent developments pushing sources to higher power and greater bandwidth. This thesis presents research in two frontiers of the science and technology of THz radiation; the generation of high power TD-THz pulses and the dynamic THz spectroscopy of an emerging new material, epitaxial graphene. To increase the SNR of conventional time domain (TD) THz sources, a novel method is proposed for high average power, high repetition rate, TD-THz generation based on an ultrafast fiber laser and optical rectification inside a GaP waveguide. A model for the THz generation is developed by combining a finite-difference frequency-domain mode solver with the 1D generation equation. The measured 150-muW average power and 3 THz bandwidth represent nearly a two order of magnitude increase over conventional TD-THz systems, and are in good agreement with the theoretical model.;Since the demonstration of the isolation of single atomic sheets of graphite, graphene has received tremendous attention due to its unique mechanical and electrical properties. These unique properties indicate graphene is a highly promising material for high-speed (THz-bandwidth) electronic devices. This thesis presents TD-THz spectroscopy of multilayer epitaxial graphene samples, with the goals of identifying the presence of a possible bandgap opening at low energies and of measuring the hot carrier recovery dynamics on picosecond timescales. The graphene transmission spectrum is shown to be remarkably flat and is used to verify the absence of a bandgap at meV energies. Optical pump -- THz probe measurements of the temperature-dependent recovery dynamics show a biexponential recovery with which is compared with theoretical predictions.;Lastly, THz detection of coherent controlled photocurrents is demonstrated for the first time in epitaxial graphene. Optical coherent control provides a method for contactless injection of ultrafast current bursts into semiconductor materials. The associated radiated THz pulse is used to verify the unique polarization independence and power scaling with theoretical predictions. The effect of background hot carriers on the coherent generation process is explored and the dephasing of the coherent current injection is observed for the first time.