Large-area transmission and reflection imaging with 640×480 pixel terahertz camera

An active terahertz (THz) imaging system that can easily be switched between a transmission and a reflection mode is developed. The system consists of a compact THz source that operates at room temperature, optical system utilizing polarization and two 640×480 pixel uncooled THz cameras. In order to take an image of a large sample, a part of the imaging system is moved at a fixed distance and a series of images taken are combined to one elongated image. Concealed nonmetallic object detection in an envelope is demonstrated.