Research on an imaging system based on cold cathode terahertz gyrotron

Terahertz waves, with the advantages of strong penetrability and low damaging, can be applied to develop non-destructive testing (NDT), security detection and medical imaging. As a vacuum electronic radiation source of high-power, long-pulse terahertz waves, gyrotron therefore has great potential in transmission imaging and NDT. A terahertz imaging system based on a cold cathode gyrotron is designed in this paper. In the system, the wave of higher-order mode generated by the gyrotron is converted to a quasi-optical Gaussian beam by a mode converter, which then passes through the object and is received by a terahertz detector for analyzing and imaging. Metal and dielectric objects are scanned in the experimental study and clear transmission images are obtained.

I. Introduction

Terahertz (THz) electromagnetic waves, which ranges from 0.1 to 10 THz [1] and lies between infrared and millimeter-wave, have been widely applied in non-destructive analysis and biomedical imaging due to their advantages in penetration, spectral resolution, spatial resolution and material protection [2]. Gyrotron, as so-called fast-wave vacuum electronic device, is based on the stimulated radiation of electron cyclotron resonance, and is one of the most important THz sources [3] that has high efficiency and can generate high power radiation in the THz frequency region. Carbon nanotube cold cathode, with fast switch-on time, room working temperature and high current density, is the excellent field electron emitter for THz gyrotron [4]. On this basis, Gyrotron based on cold cathode is finding great attraction in the development of THz radiation source that has fast response speed, compact structure and high efficiency, and is an ideal radiation source for THz imaging system [5]. Thus, a fully-sealed CNT cold-cathode 0.22THz-gyrotron developed by the University of Electronic Science and Technology of China (UESTC) is used as the THz radiation source in the imaging system [6], which is automatically controlled by Computer Numerical Control (CNC) software. The experimental results indicate that the imaging efficiency is greatly improved, and the potential of gyrotron in imaging applications is verified as well.