Research On Terahertz Fast Imaging System

Terahertz (THz) imaging has a very important academic research value and broad application prospect. Terahertz technology has been developing very fast in recent two decades. For this, THz imaging has been applied in material sciences, biomedical non-destructive evaluation and so on. THz fast imaging greatly reduces the experimental time and enhances the practicability of THz imaging.An active imaging system has been constructed using a Cassegrain reflector with the diameter of 30 cm. The system works at room temperature and 0.22 THz. We use a solid state THz source, which was focused and illuminated on the object being tested by an optical system. The reflected THz signal was collected by the same optical system. The detectors we use are self-made Nb5N6 microbolometer THz detector and commercial VDI detector. We have compared the images of two detectors. The images of the object are got by two dimensional mechanical scanning. The scanning mirror is an aluminum flat mirror fixed on a servo motor, and the servo motor is fixed on an electronically controlled rotational stage. The system is controlled by a Labview program. We get images for 5 parallel copper rods with the diameter of 1.4 cm and space of 5 cm. The imaging time is reduced from 15s to 5s by changing the reference frequency and scanning velocity. The range of the image is 20 cm X 6.5 cm. The special resolution of the images is about 1.41 cm for the two detectors.It is demonstrated to have enormous applicable prospects in detection of contraband, nondestructive evaluation and etc. In the end, we analyze the results and find some problems. Then we put forward ideas for the improvement of the system.