Development of novel waveguides in the terahertz (THz) region

Terahertz (THz) radiation, often referred to the frequency range from 0.1 to 10 THz, is the focus of an active and fast growing research community. However, this frequency range located in the electromagnetic spectrum between the microwave band and infrared band, was known as the “THz-gap” until the late 1980's. A lack of available coherent sources and detectors rendered this frequency range inaccessible. The breakthrough was achieved with the generation of THz-radiation by means of femtosecond laser pulses in the visible or nearinfrared range. The generation is usually achieved by either photo-conductive antennas or nonlinear crystals: while a biased photo-conductive antenna emits THz-radiation due to a time dependent photo-current induced by a femtosecond laser pulse, a nonlinear crystal hit by a femtosecond pulse generates a THz-pulse by difference frequency generation. Further development of THz-detectors and THz-sources like the introduction of a quantum cascade laser suitable for Terahertz frequencies provided the access to a vast variety of THz applications. In the past two decades a Terahertz technology in various fields like information and communications technology, biology and medical sciences, non-destructive evaluation and homeland security were established. Moreover, Terahertz radiation is suitable to study fundamental processes present in this frequency range like e.g. phonon excitation as well as inter-band transitions in condensed matter and rotational transitions of molecules in gases.