Brief history of THz and IR technologies

A brief history of terahertz (THz) and infrared (IR) science and technology, for learning lessons by historical evolution, is presented and discussed, identifying important (from the author’s point of view) steps for their development. THz is still a not well-known region of electro-magnetic science, even though it has been illuminated by the start of scientific and technological knowledge, since the end of the 19th century. As for the history of IR science and technology, it took many years since 1800 (W. Hershel) to reach the level of use that is recognized today. The link between IR and thermal science and applications was so strong that IR was, for a long time, synonymous with thermography. THz science and technology are showing rapid growth. IR and, especially, THz technologies have now become one of the major fields of applied research. Nowadays, they have become widely spread in their use in astrophysics, security, biomedicine, detection of hidden objects, food and art inspection, etc. The increasing requirements for fast transmission of large amounts of data will lead to the extension of operation frequencies in communications toward the THz frequency range. IR and THz medical imaging can provide guidance for surgeons in delimiting the tumor margins, help clinicians visualize the diseased area, etc. A few decades ago, IR technologies were mainly the domain of military applications. In the recent two decades, due to the widespread use of low-cost thermal uncooled arrays, many IR technology advances have been realized in civil and military applications. A large number of THz technologies' mass-market applications can’t be highlighted, as these technologies do not meet the user requirements yet, especially in terms of ease of use and costs. Still, many of the THz applications that we have now are emerging and showing their applicability in some implementations, where other methods can’t give any comprehensive information, e.g., in dry food inspection for dielectric inclusions, skin tumour margins control, THz astronomy, package and envelope inspection, etc. The brief lessons given by historical highlights in THz and IR science and applications can be important for the future developments in these directions, as history frequently opens routes for new thinking. In this brief review, the important steps can be missed. The author apologizes for these possible faults.