The progress on terahertz imaging at Capital Normal University in Beijing is presented. Our works on
Terahertz Imaging include the active and passive imaging. For the active terahertz imaging, the pulse
and continue wave terahertz imaging are studied, respectively. The active terahertz pulse imaging is
based on the terahertz time-domain spectroscopy with the probe-beam-expanded femtosecond pulse
laser and an infrared CCD detection. The active terahertz continuous wave imaging is based on a
CO2-laser-pumped terahertz coherent source and a NEC terahertz camera. The active terahertz
polarization imaging is studied. For the passive terahertz imaging, the low frequency radiometers are
used to detect the beam-scanned terahertz signal by the point-to-point scanning. The related
components and image processing methods are developed and used for the improvement of imaging
speed and resolution.
Terahertz (THz) radiation has the higher penetration to clothing, cardboard boxes, plastic packaging materials and other similar dielectrics. Its lower photon energy compared with X-rays make the detected material and the human being to be not destroyed. THz application in field of security are developed by many countries. In this research, we present a multiband of passive terahertz imaging by the thermal radiation measurement. The Noise Equivalent Temperature Difference（NETD） is obtained. The result shows that NETD of the passive imaging system is 0.8K at 94 GHz, and 1.5K at 250GHz. We found that the main source of noise is the noise from detection circuit. Finally, the improvement methods of detecting sensitivity are analyzed and discussed.