Terahertz Wave Concept and Features

Hz wave (terahertz wave) or THz ray (terahertz ray) was officially named only in the mid-to-late 1980s; before that, scientists collectively referred to it as far-infrared ray. Terahertz wave refers to electromagnetic waves with frequencies ranging from 0.1THz to 10THz, with wavelengths approximately from 0.03 to 3mm, lying between microwave and infrared. In fact, as early as one hundred years ago, scientific workers had already touched upon this band. In 1896 and 1897, Rubens and Nichols worked on this band, with infrared spectra reaching 9um (0.009mm) and 20um (0.02mm), and later records of reaching 50um. Over the following nearly one hundred years, far-infrared technology achieved many results and was already industrialized. However, research findings and data involving the terahertz band were very scarce, mainly due to the limitations of effective terahertz sources and sensitive detectors; therefore, this band was also called the THz gap. With the development of a series of new technologies and materials in the 1980s, especially the advancement of ultrafast technology, obtaining broadband stable pulsed THz sources became a quasi-conventional technique, enabling rapid development of THz technology and sparking a wave of THz research worldwide.

Features of THz rays
　　Currently, the international community has reached the following consensus on terahertz radiation: terahertz is a new radiation source with many unique advantages; terahertz technology is a highly important interdisciplinary frontier field, offering a very attractive opportunity for technological innovation, national economic development, and national security. The reason it has attracted widespread attention and has so many applications is, first, because the terahertz spectrum of matter (including transmission and reflection spectra) contains very rich physical and chemical information, so studying the spectra of matter in this band is of great significance for exploring the structure of matter; second, because terahertz pulsed light sources possess many unique properties compared with traditional light sources. The reason people pay attention to THz technology is that THz rays are ubiquitous and serve as effective clues and tools for understanding the natural world. However, compared with electromagnetic waves in other bands such as infrared and microwave, the understanding and application of THz rays remain very limited.