Terahertz wave and its new applications

The methods to generate the terahertz wave by optical rectification, photoconductive antennas, air plasmas and parametric generators are described in detail, then how to detect the terahertz wave by electro-optic sampling, photoconductive antennas and air plasmas are introduced as well. The terahertz time-domain spectroscopy and the asynchronous electro-optic sampling technique are also described. Furthermore, the applications of the terahertz technology to research fields, especially to the detection and identification of drugs are discussed. A terahertz spectrum database includes 38 kinds of drugs with a purity more than 99% is established. Moreover, the Artificial Neural Network(ANN) and a support vector machine are used to identify drugs automatically and the experimental methods and related theory are proposed to determine the purity and effective ingredients of drugs. By using a Gaussian software, individual species of drugs such as methyl-phenyl ammonia(MA), ketamine and heroin are conducted by spectral analysis, which provides a basis for implementing the drug inspection in laboratories. Finally, this paper reviews the developments of the terahertz technology briefly.