The route from fundamental physics to real world applications of THz technology

Abstract

At the end of the 80s of last century when modern laser based terahertz systems were first developed terahertz technology seemed to be only a few years away from entering wide areas of science and industrial applications. There are, in principle, endless opportunities for the use of terahertz technology starting from basic research and ending in industrial applications. However, there are also almost as many challenges as there are opportunities for a widespread application of THz technology, in particular, in an industrial environment. In basic research THz technology seems to have found its place whereas for real world applications it is still struggling for acceptance. The state of the art of THz technology will be reviewed and recent developments required for its widespread use will be discussed. This includes results from electronic devices, modern quantum cascade lasers and narrowband tunable cw as well as ultra-broadband pulsed systems based on lasers and nonlinear optics. All systems have their particular properties which make them suitable for specific measuring techniques and applications. These techniques extend from spectroscopy, time resolved measurements and imaging to all possible combinations among these methods. The applications realized so far are both very fundamental but also very close to industrial use. On the fundamental side THz systems are applied in chemistry, physics, astrophysics and biology. Material sciences use the special properties of materials in the THz spectral range to get information which are otherwise difficult to obtain. Using modern high power systems material properties can be changed and even nonlinear experiments became possible. In biomedicine and biophysics there are additional problems concerning the strong absorption of water in the THz range which require particular smart experimental methods to obtain meaningful results from THz experiments. In recent years many groups have already demonstrated the potential for industrial use of THz technology, however, it turned out to be a long way from proof of principle to real industrial use. In many cases very simple reasons prevented that THz technology was used routinely for industrial problems, like cost, complexity of the systems, or even a lack of knowledge about the THz technology. So far there are only a few promising industrial applications on the horizon where THz is the only solution for an urgent problem. Just to mention one, the determination of layer thicknesses in multilayer paint coatings on plastic, carbon reinforced plastic or metal seems to perfectly match with the properties of broadband THz systems. Pros and cons of the individual THz technologies will be shown and required future developments in order to clear the road to industrial use will be discussed.