| In this dissertation, Terahertz (THz) generation and its applications are investigated. Several ways to generate THz radiation are theoretically and experimentally demonstrated, including THz generation from nonlinear crystals via optical rectification, photoconductive antennas via time-varying current, and air plasmas based on ponderomotive force and plasma current driven by an asymmetric laser field. However, these THz generation approaches have low conversion efficiency from optical excitation power to THz radiation power. Therefore, we demonstrate a new way to recycle the residual femtosecond laser input beam, which increases the overall conversion efficiency from femsecond laser input to THz output and consequently enhances the intensity of THz radiation. Then, terahertz plasmonic lenses based on semiconductor micro-slit are demonstrated. Terahertz plasmonic lenses have not only higher terahertz transmission compared to conventional terahertz lenses but also the focal length tuning ability. One of the most important terahertz applications, terahertz spectroscopy, is also presented. Finally, several future works including nonlinear terahertz, two-dimensional terahertz plasmonic lenses, and terahertz generation from laser-induced plasma in solid targets are discussed. |
