Passive broadband terahertz camera for stand-off concealed threat identification using superconducting antenna-coupled microbolometers

Over the past several years, many groups have developed both millimeter-wave as well as terahertz imaging systems for concealed weapons detection. Typically, systems operating at the millimetre-wave range benefit from good transmission of these frequencies through common clothing materials, but provide only modest spatial resolving power at distances larger than a few meters for practical aperture sizes (dap < 1 m). Hence, these existing systems fall in the category of anomaly detectors, i.e. they intrinsically lack the performance to discriminate threat items from innocuous objects, such as cell phones, mp3 players and the like. Moreover, the radiometric performance of a passive imager has to be better than 0.5 K per frame for sufficient signal-to-noise ratio. In this joint Euro-American effort, we are developing a passive ~0.3 THz - 1 THz camera demonstrator capable of sub-Kelvin thermal resolution at video frame rates. The cryogen-free system utilizes a linear array of cryogenic antenna-coupled vacuum-bridge microbolometers, coupled to innovative all-reflective conical scanning optics and room temperature read-out electronics. First imaging results from the video rate system will be presented.