Development of Passive Submillimeter-wave Video Imaging System
in: SPIE Proceedings (2013)
Passive submillimeter-wave imaging has been in the focus of interest as a promising technology for security applications for a number of years. It utilizes the unique optical properties of submillimeter waves and promises an alternative to millimeter-wave and X-ray backscattering portals for personal security screening in particular. Possible application scenarios demand sensitive, fast, and flexible high-quality imaging techniques. Considering the low radiometric contrast of indoor scenes in the submillimeter range, this objective calls for an high detector sensitivity that can only be achieved using cooled detectors. Our approach to this task is a series of passive standoff video cameras for the 350 GHz band that represent an evolving concept and a continuous development since 2007. The cameras utilize arrays of superconducting transition-edge sensors (TES) as radiation detectors. The TES are operated at temperatures below 1 K, cooled by a closed-cycle cooling system, and coupled to superconducting readout electronics. By this means, background limited photometry (BLIP) mode is achieved providing the maximum possible signal to noise ratio. At video rates, this leads to a pixel NETD well below 1 K. The imaging system is completed by reflector optics based on free-form mirrors and integrated mechanical scanners. We present a new camera prototype featuring a linear array of 64 or 128 detectors and a linear scanner that can be adapted to different types of reflector optics for different object distances. A field of view of 1×2 m² and a frame rate of up to 25 Hz is provided.