Thermal detectors utilizing superconducting kinetic inductance and an imaging system for person security screening

Passive detection technology in submillimeter wave and THz bands is mainly utilized in astronomical imaging and security screening. Superconducting thermal detectors are one candidate for these applications. In this paper we concentrate on one particular approach based on superconducting kinetic inductance bolometers (KIBs). The technology has been developed for two main reasons: to enable integration into large detector arrays, and to enable operation with relatively compact and affordable cryogenics. Previously, we have demonstrated the basic functionality and performance of single detectors, integration into large arrays, and the capacity in concealed object detection as integrated into an imaging system. Here we review the basic structure and the properties of the KIBs, including thermal, mechanical, electrical, and quasi-optical features. We discuss the performance optimization aspects related to the heat-transfer properties of the nano-membranes defining the thermal structure of the detector. In particular, we show how the requirements of the radiation coupling set the boundary conditions for the thermal design, and discuss alternatives beyond our established technology based on absorber-coupled detectors. In addition, we describe the status of the novel fully staring imaging system aimed for person security screening, based on a 2-dimensional focal plane array with 8712 KIB-detectors. We discuss the basic functionalities of the imager, including optics, readout electronics, cryogenics, and the detectors, and present characterization and imaging results obtained with the system.