Passive Submillimeter-wave Stand-off Video Camera for Security Applications

Abstract

We present the concept and experimental set-up of a passive submillimeter-wave stand-off imaging system for security applications. Our ambition is the design of an application-ready and user-friendly camera providing high sensitivity and high spatial resolution at video frame rates. As an intermediate step towards this goal, the current prototype already achieves a frame rate of 10 frames per second and a spatial resolution below 2 cm at 8 m distance. The camera is the result of a continuous development and a unique concept that yielded first high-resolution passive submillimeter-wave images provided by cryogenic sensors in May et al. (2007). It is based on an array of 20 superconducting transition-edge sensors operated at a temperature of 450 mK, a closed-cycle cooling system, a Cassegrain-type optics with a 50 cm main mirror, and an opto-mechanical scanner. Its outstanding features are the scanning solution allowing for high frame rates and the compact and integrated system design.

Passive 350 GHz Video Imaging Systems for Security Applications

“…2) of the passive submillimeter-wave stand-off video camera presented here has evolved since 2007 and has been published before [9,12,18,[20][21][22]. Table 1 gives an overview of the different camera prototypes and their main parameters.…”

“…The sensitivity of TES is determined by the thermal design, which has to be adapted to the background radiation power, and the working temperature [27]. At a working temperature of about 400 mK and a typical 300 K background signal of 100 pW, the TES noise is at a level of about 3·10 −16 W/ √ H z [21], fulfilling the BLIP condition and still leaving some headroom for for noise degradation by multiplexed readout. The TES have a time constant of about 70 μs in feedback mode, corresponding to the signal bandwidth.…”

“…Using this approach, high resolution passive submillimeterwave video imaging at a frame rate of up to 10 Hz was demonstrated. This system was first presented in 2010 and has been described in detail elsewhere [18,21].…”

“…The spiraliform scanning concept results in circular images and a non-uniform scanning density [21], and the image generation as a superposition of the individual detector signals is complex and time-consuming. Other limits of this concept are a restricted image angle and a restricted array size.…”

“…At a frame rate of 25 Hz, it provides a smooth and stable video stream without scanning artifacts. Major issues of previous camera prototypes [18,21] therefore have been resolved. Example video frames shot with this camera are shown in Fig.…”