Ultrasensitive Far-IR Kinetic Inductance Detector Arrays for Space

We propose a program to retire the key technical risk of far-infrared space astrophysics missions recently recommended by Astro2020. We will demonstrate large arrays of kinetic inductance detectors (KIDs) with the sensitivity and format required to deliver the massive scientific potential of spectroscopy aboard cryogenic spaceborne observatories, most urgently in a near-term Probe-class facility like our PRIMA concept, and eventually in a far-infrared (IR) flagship similar to Origins. We will build on APRA development and ground-based and balloon-borne arrays to build packaged focal planes that can be directly inserted into phase A/B designs for a near-term probe. We will demonstrate two arrays at wavelengths that bound the envisioned far-IR range: 25 microns and 212 microns, with pixel pitch, readout density, and size informed by these concept studies. Our two arrays will meet all of the essential performance and system-level requirements imposed by a near-term far-IR Probe: 1. per-pixel noise equivalent power (NEP) below 1 x 10^-19 W Hz^-1/2, 2. >65% optical efficiency relative to light incident on the pixel's coupling optic, 3. high scientific utility in the face of cosmic-ray interactions in space, and 4. packaging into a flight-ready housing with at least 8000 pixels demonstrating >80% yield and acceptable cross talk. KIDs are a strong choice for future far-IR observatories because they naturally enable the many-kilopixel arrays necessary for the wide-field spectral surveys. KIDs have demonstrated kilopixel arrays in a range of ground-based and balloon-borne missions, showing as-designed performance---background-limited for these platforms. Given these developments as well as recent developments in KID sensitivity, we are now ready to demonstrate KIDs for flight. We begin with the necessarily holistic design of the two arrays. Prior work provides a good understanding of the material properties and fabrication limitations, as well as demonstrations of 1000-pixel multiplexing. We will design the integrated low-volume KID inductor with the microlens concentrating optic to ensure good efficiency. Small subarray tests are already underway to vet the designs. Full array prototypes will follow to demonstrate yield as well as the key performance requirements, reading out four circuits simultaneously to show system-level operation and measure cross talk. Finally, we will design and build flight-worthy housings for the two arrays, assemble and subject them to vibration and particle testing, then re-verify performance to reach Technology Readiness Level 6 (TRL). We submit that the current state of the technology is TRL 4, given fielded instruments meeting their requirements, and our work will position the large low-background far-IR KID arrays at TRL 6: “system demonstration in a relevant end-to-end environment.” This work will be concurrent with the Probe mission formulation, ensuring the suitability of the demonstrations for their purpose. The resulting prototype flight arrays will optimize scientific capability and clarify observatory interfaces. Our work will provide design rules for the other far-IR wavebands at intermediate wavelengths. Demonstration of these arrays would be largely standard engineering and could be undertaken in project phase A/B. This proposed 2-year activity is an extension of a 1-year award in FY23 to the same team (with Bradford as PI). This work is rapidly converging on pixel designs, but continued funding for FY24 and FY25 is required to demonstrate the array-level operation and position KID arrays for PRIMA (or another step-1 selected far-IR Probe) preliminary design review (PDR) in 2026.

The Strategic Astrophysics Technology program (SAT) supports focused development efforts for key technologies to the point at which they are ready to feed into major missions in the three science themes of the Astrophysics Division: Exoplanet Exploration, Cosmic Origins, and the Physics of the Cosmos. This program is specifically designed to address middle technology readiness level (TRL) "gaps" between levels 3 and 6: the maturation of technologies that have been established as feasible, but which are not yet sufficiently mature to incorporate into flight missions without introducing an unacceptable level of risk.

This is a mature technology (TRL 7+) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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