ABSTRACT
This chapter deals with various techniques employed to generate efficient Terahertz (THz) radiation (frequency: 300 GHz to 3 THz) through nanostructures or semiconducting materials. These techniques include a photoconductive emission mechanism, which is based on irradiating the gap of the photoconductive antenna (PCA), optical rectification (OR) mechanism in which the optical nonlinearity of the material is exploited by irradiating the crystal by optical excitation, and so forth. Transient current (TC) effect is explained in detail, which includes surface field effect and photo-Dember effect. Since optical properties of nanoparticles can be tailored by changing the number of parameters, including their orientations with respect to the incident laser field, they can be exploited for the generation of THz radiation. In view of the surface plasmon's excitation on metal films deposited on a shallow grating, surface plasmon-assisted THz radiation generation is discussed. An experimental setup for the THz radiation generation by metal gratings is given and explained.
Quantum dot (QD) materials exhibit unique properties owing to their extremely small size and quantum confinements in all three dimensions. The implanted QDs are found to act as an active medium in the host crystal, which contributes to the THz signal conversion. This phenomenon and the corresponding results are explained in detail. Further, THz radiation generation by random two-dimensional (2D) metallic structures is presented with a schematic diagram and explanation. Finally, a technique for generating THz radiation by carbon nanotube array is discussed along with a detailed mathematical treatment.
