Terahertz radiation refers to far-infrared electromagnetic radiation with a frequency in the range of 0.1~10THz. Terahertz imaging was first proposed by Hu Binbinm et al. in 1995. The principle is to use terahertz waves of known waveforms as imaging rays, and the intensity and phase of the terahertz waves transmitted through the sample contain the space of the complex permittivity of the sample. distribution; the two-dimensional information of the intensity and phase of the transmitted terahertz wave is recorded, and after appropriate digital processing and spectral analysis, a three-dimensional image of the terahertz wave of the sample can be obtained. A remarkable feature of terahertz imaging is the large amount of information, each image source corresponds to a terahertz time-domain spectrum, and the terahertz frequency spectrum of each point can be obtained by performing Fourier transform on the time-domain spectrum. Since terahertz detector arrays are currently very expensive, typical terahertz imaging is achieved by raster scanning with unit detectors.

Because of the high frequency of terahertz, its spatial resolution is very high, and because the terahertz pulse is very short, it has high temporal resolution; in addition, the energy of terahertz is very small and will not cause damage to matter, So compared with X-ray, it has great advantages. Some of the main advantages of terahertz imaging include that terahertz radiation can penetrate with little attenuation, such as ceramics, fats, cloth, plastics, etc., and can penetrate walls and smoke without damage; the time-domain spectral signal-to-noise ratio of terahertz is very high. high, so terahertz is ideal for imaging applications.

 

The main bottleneck of terahertz imaging is to generate a strong enough effective signal. Except for free electron lasers, most of the current terahertz radiation sources have very low power; many components required for terahertz imaging have not yet been developed; terahertz imaging distance short. Current terahertz imaging requires the target to be within tens of centimeters of the terahertz radiation source; the time for terahertz imaging data acquisition is long.