Ultrafast THz Photonics and Applications

Abstract

Ultrafast THz photonics the topic of this chapter describes the union of optical and ultrafast laser capability with electronics to achieve frequency performance and bandwidths extending well into the THz frequency range. With the demonstrated capability to create and to measure subpicosecond electrical signals that are much faster than those produced and measured by any other method, THz photonics will help determine the direction for the development of new materials and ultra high performance technologies of the future. In the Guided-Wave THz Photonics Section the generation, measurement and applications of these very short electrical pulses are described. They can be used as probes for short electrical pulse studies and the consequent characterization of transmission lines is described, including the measurement of Cherenkov radiation. The performance of transmission lines is compared with metal THz waveguides, whose characterization is also presented. Results for superconducting transmission lines and dielectric THz waveguides are given. In the Freely Propagating Wave THz Photonics Section recent work demonstrating the generation of freely propagating THz radiation (1 THz =33.3 cm−1 =4.1 meV) via material and electronic excitation by ultrashort laser pulses is presented. The generation of short pulses of THz radiation, by the passage of a short optical pulse through a nonlinear optical material, is also described. A cw photomixer capable of producing tunable radiation by beating together two laser beams is presented. The most developed THz application is THz time-domain spectroscopy (THz-TDS) which is described in detail. The combination of THz-TDS with THz beams will be shown to have some powerful advantages compared to traditional c.w. spectroscopy. The efficacy of THz-TDS is demonstrated by the presented characterizations of water vapor, flames, sapphire, high-resistivity silicon, n and p-type semiconductors, normal and high Tc superconductors, molecular vapors and liquids.