Terahertz Electromagnetic Waves. Applications

The study of the terahertz (THz) domain was revitalized and facilitated at the end of the 1980s, thanks to the emergence of new techniques and technologies, initially optoelectronic, then based on the frequency upgrading of electronic components or the development of new nanometric components. In addition to academic research, this research effort has been stimulated by the many applications that have been identified. These applications are based on the transparency of opaque materials in the visible or infrared (imaging applications for industrial control, medicine or security – personal inspection –), the existence of unique spectral signatures for certain molecules (applications for the identification of molecules by spectroscopy, for example, in the fields of the environment, security, biophysics, astrophysics...), and the possibility of modulating these waves at very high frequencies (high-speed telecoms at very short distances). This article first presents the applications of terahertz technology in the field of scientific instrumentation, which is currently without doubt the biggest market for terahertz devices and systems. Secondly, it describes the security and military fields, to which a very large proportion of terahertz research is now dedicated. The third part of the article is devoted to industrial applications. Although few terahertz systems are actually installed in companies today, it is conceivable that terahertz technology will eventually occupy a number of niches, complementing already widespread techniques such as infrared and visible spectroscopy, X-ray diffraction and so on. The following paragraph describes the application of terahertz imaging to the examination of works of artistic heritage, involving procedures very similar to those used in industrial applications. The development of terahertz instrumentation and techniques for medicine and biology is then presented. Often described as the investigative technique of the future for medicine, terahertz imaging is nonetheless struggling to establish itself definitively. For biology, applications seem easier to implement. In environmental applications, thanks to their spectral specificity, terahertz waves provide information that complements traditional techniques such as lidar, or even unique information, as certain molecules only display an original spectral signature in the terahertz range. Finally, the increasing frequency of telecommunications is bringing them steadily closer to the terahertz region. On the one hand, data flows at laboratory test level exceed 100 Gbits/s, and on the other, free-space transmission systems are being developed, mainly for use inside buildings, using a terahertz wave as the signal carrier. The article concludes with the authors' thoughts on the future of terahertz science and technology. This is followed by...