Primary Investigation Of THz Laser Transmittion Imaging Technique

THz radiation is the far infrared radiation whose frequency is between 0.1THz and 10 THz. Owing to its special spectrum position of THz radiation, it make great sense to image with THz radiation, especially in security applications. The investigation of THz imaging depends on the choice of laser source and detector. Only THz laser pumped by CO₂ laser which has the advantage of compactness, high and stable output power, become a commercial product. Now days it still not well developed in the detection field, and slow response and low sensitiveness become the bottleneck of THz imaging technique. In this paper the imaging system using coherent SIFIR-50 laser and P4-42 detector is investigated.The transparent properties of some samples were first researched, such as polythene, polytetrafluoroethylene, and paper, and we got a series of transparent curves at different wavelengths. By these curves we got the absorption coefficients after fitting. Finally, we analyzed the relationship between the absorption coefficients and wavelengths.THz imaging system was designed in this paper, which could image through the screen made of papers. We had clear images of letters with a width of about 3mm and the metal plate with a width of about 0.3mm which were packed by 2 layers of papers. The experiment took only 30 minutes to get a 60×60 image. This research offer technique support for security detection by virtue of the THz imaging system using commercial products. Water has a strong absorption of THz radiation, and a little water could absorb all the THz radiation. As the nervation of leaf having the most water in leaf, we could see nervation clearly after THz imaging. We got the images of polythene and polytetrafluoroethylene table, by which we could see the inner density and frame distribution, so we could test the quality of product after produced.We got a series of images using THz transmission system, which shows that THz Imaging system will have important applications in the fields of quality control, security detection, and food fields.