The typical pulse width of terahertz pulse is in the order of picoseconds, which can not only facilitate the study of time resolution, but also effectively suppress the interference of far-infrared background noise through sampling measurement technology. At present, pulsed terahertz radiation usually has a low average power of terahertz rays. However, due to the high peak power of terahertz pulse and the real-time power of terahertz pulse obtained by coherent detection technology, it has a high signal-to-noise ratio. At present, the signal-to-noise ratio of time-domain spectrum system can reach 10 5 or higher.
Terahertz pulse source usually contains only a few cycles of electromagnetic oscillation, and the frequency band of a single pulse can cover the range from GHz to tens of THz. Vibration and rotation energy levels of many biological macromolecules, phonon vibration energy levels of dielectrics, semiconductor materials, superconducting materials, thin film materials, etc. Belonging to the terahertz band range. Therefore, terahertz time domain spectroscopy, as an effective means to detect the information of substances in terahertz band, is very suitable for measuring the absorption spectrum of substances and can be used for qualitative identification.
Terahertz photon energy is low, and the photon energy with the frequency of 1 terahertz is only about 4 mev, so it is not easy to destroy the detected substance.
Many nonmetallic nonpolar materials have little absorption of THz rays, so it is possible to detect the internal information of materials by combining with corresponding technologies. Such as ceramics, cardboard, plastic products, foams, etc. It is transparent to terahertz electromagnetic radiation, so terahertz technology can be used as a non-ionizing and coherent complementary radiation source of X-rays for security monitoring in airports, stations and other places, such as detecting hidden smuggled goods, including guns, explosives and drugs. And detecting the welding condition of the integrated circuit. Polar substances have a strong absorption rate of THz electromagnetic radiation, especially water. Various measures should be taken to avoid the influence of water in terahertz spectroscopy. However, in terahertz imaging technology, this characteristic can be used to distinguish different States of biological tissues, such as the distribution of fat and muscle in animal tissues, the diagnosis of the damage degree of human burn sites, and the distribution of water in plant leaf tissues. Compared with other imaging technologies, terahertz imaging technology obviously improves the resolution and depth of field of the detected image (ultrasonic, infrared and X-ray technologies can also improve the image resolution, but millimeter wave technology has not improved significantly). In addition, terahertz technology has many unique characteristics, such as less scattering in heterogeneous materials, and being able to detect and measure water vapor content.
Terahertz spectroscopy technology not only has high signal-to-noise ratio, but also can quickly analyze and identify the subtle changes of sample components. Terahertz spectroscopy is a non-contact measurement technology, which enables it to measure the physical information of semiconductors, dielectric films and bulk materials quickly and accurately. In view of the characteristics of THz rays, it will have a far-reaching impact on communication, radar, astronomy, medical imaging, biochemical identification, material science, safety inspection and other fields, and then change people's production and life.