Terahertz Sources, their Technology and Applications

There exists a significant interest to use THz signals for security applications. The required signal sources need to be small in size, easy to operate and not to be too costly. A review is first presented of the approaches used so far. Then the contributions made by the laboratory of this author are to be described. A particularly promising technique is the use of ballistic resonance in heterojunction structures. A more classical approach uses the step-recovery diode equivalence of heterostructures. Another technique is based on pulsed optics from Q-switched lasers and optical mixing at various materials. This can be extended also to the involvement of low-cost femtosecond laser pulsers together with a dc bias voltage. Instead of solid-state ballistics, corresponding laser-pulse initiated field emission of electron bunches in a THz vacuum resonator can be employed, too. The relevant heterojunction technology is to be described. The device structures will be given as to be inserted together with the required antennas in THz waveguides. Experimental results are to be presented. Among the many applications also THz matrix and bar codes are to be discussed for documentation. Here also early experimental efforts are described. An interesting question concerns the use of THz RFID's on flexible substrates, including liquid crystal structures.