In recent years, the research and application of terahertz technology has shown significant technological advantages and industrialization prospects in many fields such as food/drug testing, security inspection equipment, medical diagnosis, and semiconductor material inspection. The emergence of ultrafast fiber laser pointer has further promoted the commercialization of terahertz technology. Compared with the complex and huge volume of optically pumped terahertz gas lasers and the expensive price of Ti:Sapphire lasers, ultrafast fiber lasers are favored by the market due to their high integration, small size, simple operation, and easy mass production.
What is terahertz? Terahertz (THz, 1012Hz) usually refers to electromagnetic waves with a frequency in the range of 0.1~10THz (corresponding to a wavelength of 3mm~30μm). In the field of optics, it is called far infrared, and in the field of electronics, it is called far infrared. It is sub-millimeter wave, ultra-microwave, etc., between microwave and infrared light in the entire spectrum. Compared with electromagnetic waves in other frequency bands, the main characteristics of terahertz include:
1) Low photon energy (safety), much lower than X-ray photon energy, will not produce harmful ionization to biological tissues, and is suitable for in vivo detection of biological tissues;
2) High penetration: Femtosecond pulse width and extremely high time resolution make terahertz waves have good penetration to many dielectric materials and non-polar materials, and can penetrate walls under low loss conditions , Ceramics, carbon plates, cloth, plastics, etc. for perspective imaging;
3) Fingerprint spectral properties: The absorption spectrum and dispersion characteristics of many organic molecules are in this region, and the terahertz spectrum of each substance contains rich physical and chemical information.
Terahertz radiation source is the key to whether terahertz technology can be transformed into actual productivity. There are currently three types of terahertz sources: terahertz sources based on vacuum electronics; terahertz sources based on photonics; terahertz sources based on semiconductors. Among them, terahertz sources based on photonics mainly use ultrafast green laser pointer as terahertz excitation light sources.