Scalable readout of terahertz wave multiplex inputs from thousands of detectors

Superconducting detectors have been shown to be capable of creating images using radiation in terahertz and far infrared frequency bands for uses such as improved thermal imaging. One approach for detecting such sub-millimeter waves, called kinetic inductance bolometer (KIB) technology, can scale into arrays and operate at higher, more cost-effective cryogenic temperatures. New work looks to provide a missing piece for multiplexing such detectors.

Sipola et al. present a novel way to multiplex the readout in KIB arrays using a technique called serial addressed frequency excitation (SAFE) and have demonstrated its use in experiments with a stand-off laboratory-scale imager. Building on their work on scaling other components of terahertz detectors in to kilopixel arrays, the group turned to developing a simpler alternative to frequency-division multiplexing techniques typically used for microwaves and radio waves that rely more on high-speed electronics.

The resulting readout has accommodated an imager made with more than 8,000 detectors that boasts signal-to-noise degradation significantly less than the group’s projected worst-case degradation limits.

It marks one of the first demonstrations of a terahertz imager with scalable detector technology and enough sensitivity to be used in thermal imaging for security applications. Many previous attempts have lacked the sensitivity to do this and require artificial illumination to achieve sufficient dynamic range.

“We are looking into thermal radiation emitted by the human being, a concept similar to infrared cameras showing the temperature profiles of the imaged targets,” said author Juha Hassel. “Infrared radiation, however, does not penetrate the clothes.”

The group looks to improve the sensitivity of their technology on imaging at sub-millimeter wavelengths and expanding its applications, with potential further applications in astronomical imaging.

Source: “Multiplexed readout of kinetic inductance bolometer arrays,” by Hannu Sipola, Juho Luomahaara, Andrey Timofeev, Leif Grönberg, Anssi Rautiainen, Arttu Luukanen, and Juha Hassel, Review of Scientific Instruments (2019). The article can be accessed at https://doi.org/10.1063/1.5091754 .