Much research has shown that terahertz waves can penetrate a number of materials while generating images with high spatial resolution. A number of these terahertz imaging solutions rely on continuous-wave radiation sources like a backward-wave oscillator (BWO). BWOs offer high output power, good wave-front quality, working-wavelength tunability, and a high signal-to-noise ratio. At China’s Southeast University, a continuous-wave (CW) terahertz imaging system using a BWO as source, a Golay-Cell as a detector, and an oscilloscope as a data-acquisition unit has been developed by Gang Chen, Jie Pei, Fei Yang, Xiao Yang Zhou, Z.L. Sun, and Tie Jun Cui.

The system’s software, which is based on the oscilloscope, is designed to control object movement as well as the capture and display of continuous terahertz-wave image data. To show the system’s validity at room temperature, the team tested the imaging of different objects at 450 and 890 GHz. The system was affected by humidity, thickness, and material properties. In addition, imaging resolution was discovered to be better as incident frequency increased. The translation step also impacted imaging, showing that the appropriate frequency and translation step must be chosen to meet practical imaging requirements. See “Terahertz-Wave Imaging System Based On Backward Wave Oscillator,” IEEE Transactions On Terahertz Science And Technology, Sept. 2012, p. 504.