Study On Terahertz Fast-scanning Imaging

Terahertz technology is regarded as an important frontier science and technology, and it has a rapid development in recent decades. Because of its unique properties, terahertz has a great future in imaging and medical detection. Researchers are in favor of terahertz continuous-wave imaging technology with the advantages of simple structure, fast scanning speed, good imaging quality, and normal temperature work. A fast terahertz continuous-wave scanning imaging system is introduced, because the scanning speed and imaging quality reported cannot reach the demand of practical application. The system can increase the scanning speed and improve the imaging quality. A fast tunable terahertz parametric oscillator source is introduced to use as the imaging source in future terahertz imaging system.The main work of this paper is listed as follows:1. This paper introduces a fast terahertz continuous-wave scanning imaging system. A wire grid polarizer is used to divide terahertz wave, the signal-to-noise ratio of the system is increased by the introduction of reference terahertz wave. Through the LabVIEW software programming, serpentine columnar scanning method and the real-time signal acquisition is controlled by computer to reduce the scanning time. The scanning speed can reach 10 pixels per second. When the output frequency is 4.3THz, the resolution of scanning image can reach 0.1mm. It takes 17 minutes to scan a sample with the size of 1cm×1cm. Clear scanning image of leaves, pharmaceuticals and biological tissues are achieved.2. Digital image processing is used to improve the image quality. The gray-level histogram, unsharp masking and high boost filtering, corrosion and expansion processing are selected to improve the gray imaging quality. Pseudo color processing is used and color images are obtained.3. Fast tunable terahertz parametric oscillator system is built with LiNbO3 crystal. The line-width characteristics of Stokes light are investigated by changing the cavity length, pump pulse-width and tuning angle. The tuning range is 1.2-2.4THz, the maximum of pulse energy is 368.6nJ at the frequency of 1.6THz. We design a fast tunning TPO ring cavity system depends on Roland circular principle, and it can keep the position of terahertz wave fixed when changing the tuning angle.