Sub-THz kinetic inductance bolometer arrays and cameras for security applications

Sub-THz imaging (0.1-1 THz) is an emerging technology for stand-off security screening of concealed objects in mass transit and public areas.

Passive imaging technology based on detection of weak thermal emission in the sub-mm wave band sets demanding requirements for imaging systems to operate with high radiometric (0.1 K) and diffraction-limited spatial resolution at video rates. This in turn leads to demanding requirements of having ~10,000 or more image pixels to cover the field of view of the full human body. The number of detector pixels is often compromised by using opto-mechanical scanners leading to reduction of per-pixel dwell time and hence increasing the effective noise bandwidth.

We developed technology for large-format sub-mm wave staring 2D focal plane arrays based on superconducting NbN kinetic inductance bolometer resonators operating in the phonon noise limit at bath temperatures of ~ 7 K. The bolometers are frequency division multiplexed with ratios ~100:1 per channel. Multiple channels form 2D focal plane arrays which are utilised in kilo-pixel sub-mm wave cameras. We discuss both the performance of the bolometers and the full imaging systems including sub-mm wave optics [1,2,3].

1. Optical and electrical characterisation of a large kinetic inductance bolometer focal plane array.
   A.V. Timofeev, J. Luomahaara, L. Grönberg, A. Mäyrä, H. Sipola, M. Aikio, M. Metso, V. Vesterinen, K. Tappura, J. Ala-Laurinaho, A. Luukanen, and J. Hassel,
   IEEE Trans. On Terahertz Science and Technology, VOL. 7, NO. 2, MARCH 2017.
2. Bolometric kinetic inductance detector technology for sub-millimetre radiometric imaging.
   J. Hassel, A. V. Timofeev, V. Vesterinen, H. Sipola, P. Helistö, M. Aikio, A. Mäyrä, A. R. Luukanen, L. Grönberg,
   Proc. SPIE 9651, Millimetre Wave and Terahertz Sensors and Technology VIII, 96510G (2015).
3. Submillimeter-Wave Kinetic Inductance Bolometers on Free-Standing Nano-membranes.
   A.V. Timofeev, V. Vesterinen, P. Helistö, L. Grönberg, J. Hassel, A. Luukanen,
   Superconductor Science and Technology 01 / (2014); 27(2).