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Photon-counting detectors address the single most difficult technology challenge for the Origins Space Telescope (OST) and are highly desirable for reaching the ~ 10^-20 W/√Hz sensitivity permitted by the observatory. One objective of this facility is rapid spectroscopic surveys of the high redshift universe at 420 – 800 μm, using arrays of integrated spectrometers with moderate resolutions (R = λ/Δλ ~1000), to explore galaxy evolution and growth of structure in the universe. A second objective is to perform higher resolution (R > 100,000) spectroscopic surveys at 20–300 μm for exploring the distribution of the ingredients for life in protoplanetary disks. Lastly, the OST aims to do sensitive mid-infrared (5–30 μm) spectroscopy of rocky planet atmospheres in the habitable zone using the transit method. These objectives represent a well-organized community agreement, but they are impossible to reach without a significant leap forward in detector technology, and the OST is likely not to be recommended if a path to suitable detectors does not exist.
Our team is developing photon-counting Kinetic Inductance Detectors (KIDs) for the OST. Since KIDs are highly multiplexable in nature their scalability will be a major improvement over current technologies that are severely limited in observing speed due to small numbers of pixels. Moreover, KIDs are an established strong competitor to TESs and have achieved NEP ~ 1.5—3x10^-19 W/√Hz in a fully operational 1000-pixel science grade array made by SRON under the SpaceKID program. To reach the sensitivities for OST we are developing KIDs made from very thin aluminum films on single-crystal silicon substrates. Under the right conditions, small-volume inductors made from these films can become ultra-sensitive to single photons >90 GHz. Understanding the material physics and electrodynamics of excitations in these superconductor-dielectric systems is critical to performance. We have achieved world-record material properties, which are within requirements for photon-counting: microwave quality factor of 0.5 x 10^6 for a 10-nm aluminum resonator at single microwave photon drive power, residual dark electron density of < 5 /µm^3 and extremely long excitation lifetime of ~ 6.0 ms. Using a detailed model we simulated our detector when illuminated with randomly arriving single photon events and show that photon counting with >95% efficiency at 0.5 - 1.0 THz is achievable. Combined with µ-Spec - our Goddard-based on-chip far-IR spectrometer - these detectors will enable the first OST science objective mentioned above, and provide a clear path for the shorter wavelength objectives as well.
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