Towards high-sensitivity and high-resolution submillimeter-wave video imaging
in: Optical Engineering (2011)
Against a background of newly emerged security threats, the well-established idea of utilizing submillimeter-wave radiation for personal security screening applications has recently evolved into a promising technology. Possible application scenarios demand sensitive, fast, flexible and high-quality imaging techniques. At present, best results are obtained by passive imaging using cryogenic microbolometers as radiation detectors. Building upon the concept of a passive submillimeter-wave stand-off video camera introduced previously, we present the evolution of this concept into a practical application-ready imaging device. This has been achieved using a variety of measures such as optimizing the detector parameters, improving the scanning mechanism, increasing the sampling speed, and enhancing the image generation software. The camera concept is based on a Cassegrain-type mirror optics, an opto-mechanical scanner, and an array of 20 superconducting transition-edge sensors (TES) operated at a temperature of 450‒650 mK, and a closed-cycle cryogen-free cooling system. The main figures of the system include: a frequency band of 350±40 GHz, an object distance of 7‒10 m, a circular field of view of 110 cm diameter at 9 m distance, a spatial resolution below 2 cm, a noise equivalent temperature difference (NETD) of 0.1‒0.4 K, and a maximum frame rate of 10 Hz.