Future space-based far infrared astronomical observations require background limited detector sensitivities and scalable focal plane array solutions to realize their vast potential in observation speed. In this work, a focal plane array of lens absorber coupled kinetic inductance detectors (KIDs) is proposed to fill this role. The figures of merit and design guidelines for the proposed detector concept are derived by employing a previously developed electromagnetic spectral modeling technique. Two designs operating at central frequencies of 6.98 and 12 THz are studied. A prototype array of the former is fabricated, and its performance is experimentally determined and validated. Specifically, the optical coupling of the detectors to incoherent distributed sources (i.e., normalized throughput) is quantified experimentally with good agreement with the estimations provided by the model. The coupling of the lens absorber prototypes to an incident plane wave, i.e., aperture efficiency, is also indirectly validated experimentally matching the expected value of 54% averaged over two linear polarizations. The noise equivalent power of the KIDs is also measured with limiting value of 8 × 10-20W\√Hz at the bath and radiator temperatures of 130 mK and 2.7 K, respectively, under negligible optical loading.

Scaling astronomical detectors and quantum devices to larger and larger sizes will require more readout lines. A problem with extra readout lines is the complexity and cost of many coaxial cables in parallel. Furthermore, the thermal loading on the coldest stages via thermal conductivity should be kept at a minimum. Delft Circuits provides a 8-channel flexible cabling solution based on stripline technology with Ag or NbTi conductors and polyimide dielectric (flexline) as a solution to these problems. However, a compact and light-tight flex-to-chip interface is lacking, and this would be key to unlocking its full scaling and lightweight potential. Here, we present the design and measurements of a flexline to PCB interface for cryogenic detectors. The flexline is connected securely via a spring-loaded pressing tool, ensuring reliable contact even after thermal contraction. To reduce stray radiation, the chip and connector assembly sits in a light-tight setup. The connector spans a width of 20 mm along one edge of the chip, illustrating the compact design. We show that the flexline connector has an insertion loss of -2 dB at 7 GHz using a probe measurement at room temperature. We also demonstrate the connector with a test chip with kinetic inductance detectors in a dilution refrigerator cooled to 40mK.

Studying the polarization and spectral distortion of the Cosmic Microwave Background (CMB) in tandem with intensity fluctuations of the Cosmic Infrared Background (CIB) allows us to verify our assumptions on cosmic inflation and investigate the dynamics and evolution of galaxy clusters in the last 10 billion years. Because of its broadband emission and being an all-sky extended source, observing the entire CMB in detail is a very time-consuming and expensive exercise. Fortunately, in the last few years, the on-chip superconducting spectrometer technology has moved out of the lab and into the telescope. With its compact size and background-limited sensitivity, this family of instruments is particularly well-suited for fast and large area observations in a relatively unexplored range of the electromagnetic spectrum. However, recent examples of this technology do not yet reach the requirements needed for large spectroscopic and polarimetric surveys of the CMB. We formulate several of these requirements and introduce novel on-chip components and fabrication techniques. We introduce a cross-over to enable distinguishing signal polarization, minimize signal loss by locally optimized lithography of a coplanar-waveguide (CPW), lower the spectral resolution of microstrip filters by deposition of a dielectric layer, and increase the yield of the spectrometer array by removing individual line shorts. These together have culminated in the successful fabrication of a fourteen-spaxel IFU.

The presence of quasiparticles typically degrades the performance of superconducting microwave circuits. The readout signal can generate nonequilibrium quasiparticles, which lead to excess microwave loss and decoherence. To understand this effect quantitatively, we measure quasiparticle fluctuations and extract the quasiparticle density across different temperatures, readout powers, and resonator volumes. We find that microwave power generates a higher quasiparticle density as the active resonator volume is reduced and show that this effect sets a sensitivity limit on kinetic inductance detectors. We compare our results with theoretical models of direct microwave photon absorption by quasiparticles and conclude that an unknown, indirect mechanism plays a dominant role in quasiparticle generation. These results provide a route to mitigate quasiparticle generation due to readout power in superconducting devices.

Low-loss deposited dielectrics are beneficial for the advancement of superconducting integrated circuits for astronomy. In the microwave band (approximately 1-10 GHz) the dielectric loss at cryogenic temperatures and low electric field strengths is dominated by two-level systems. However, the origin of the loss in the millimeter-submillimeter band (approximately 0.1-1 THz) is not understood. We measured the loss of hydrogenated-amorphous-SiC films in the 0.27-100-THz range using superconducting-microstrip resonators and Fourier-transform spectroscopy. The agreement between the loss data and a Maxwell-Helmholtz-Drude dispersion model suggests that vibrational modes above 10 THz dominate the loss in hydrogenated amorphous SiC above 200 GHz.

Disordered superconductors offer new impedance regimes for quantum circuits, enable a pathway to protected qubits, and can improve superconducting detectors due to their high kinetic inductance and sheet resistance. The performance of these devices can be limited, however, by quasiparticles—the fundamental excitations of a superconductor. While experiments have shown that disorder affects the relaxation of quasiparticles drastically, the microscopic mechanisms are still not understood. We address this issue by measuring quasiparticle relaxation in a disordered β-Ta film, which we pattern as the inductor of a microwave resonator. We observe that quasiparticle recombination is governed by the phonon scattering time, which is faster than conventional recombination in ordered superconductors. We interpret the results as recombination of localized quasiparticles, induced by disorder, which first delocalize via phonon absorption. We analyze quasiparticle relaxation measurements on superconductors with different degrees of disorder and conclude that this phenomenon is inherent to disordered superconductors.

We present the science drivers for the far-infrared enhanced survey spectrometer (FIRESS), one of two science instruments on the PRobe Infrared Mission for Astrophysics. FIRESS is designed to meet science objectives in the areas of the origins of planetary atmospheres, the co-evolution of galaxies and supermassive black holes, and the buildup of heavy elements in the universe. In addition to these drivers, FIRESS is envisioned as a versatile far-infrared spectrometer, capable of addressing science questions in most areas of astrophysics and planetary astronomy as part of a dominant General Observer (GO) program with 2/3 of the current science cases using FIRESS. We summarize how the instrument design choices and parameters enable the main science drivers as well as a broad and vibrant GO program.

The PRobe far-Infrared Mission for Astrophysics (PRIMA) is under study as a potential far-IR space mission, featuring actively cooled optics, and both imaging and spectroscopic instrumentation. To fully take advantage of the low background afforded by a cold telescope, spectroscopy with PRIMA requires detectors with a noise equivalent power (NEP) better than 1 × 10 ^-19 W Hz ^-12. To meet this goal, we are developing large format arrays of kinetic inductance detectors (KIDs) to work across the 25–250 μm range. Here, we present the design and characterization of a single pixel prototype detector optimized for 210 μm. The KID consists of a lens-coupled aluminum inductor-absorber connected to a niobium interdigitated capacitor to form a 2 GHz resonator. We have fabricated a small array with 28 KIDs, and we measure the performance of one of these detectors with an optical loading in the 0.01–300 aW range. At low loading, the detector achieves an NEP of 9 × 10 ^-20 W Hz ^-1/2 at a 10 Hz readout frequency. An extrapolation of these measurements suggests this detector may remain photon noise limited at up to 20 fW of loading, offering a high dynamic range for PRIMA observations of bright astronomical sources.

We developed, characterized, and verified an alignment procedure for the DESHIMA 2.0 instrument, an ultra-wide-band spectrometer operating between 200 and 400 GHz, at the ASTE telescope. To this end, we mounted the warm optics, consisting of a modified Dragonian dual reflector system, on a motor-controlled hexapod. Crucial in the alignment procedure is our sky chopper, which allows fast beam switching. It has a small entrance and exit aperture coupling to the (cold) sky, which creates a measurable signal with respect to the warm cabin environment. By scanning the instrument beam across the entrance aperture of the sky chopper using the hexapod, we found the hexapod configuration that produced the lowest signal on our detectors, implying that the beam is coupled fully to the cold sky and not the warm cabin. We first characterized the alignment procedure in the laboratory, where we used a vat containing liquid nitrogen as the cold source behind the sky chopper. Then, we applied the alignment procedure to DESHIMA 2.0 at ASTE. We found that the alignment procedure significantly improved the aperture efficiency compared with previously reported values of the aperture efficiency of DESHIMA at ASTE, which indicates the veracity of the alignment procedure.

The Astro2020 Decadal Survey recommended a new line of astrophysics observatories intermediate in scale between MIDEXs and Flagship-class observatories. In response, NASA created the Astrophysics Probe Explorer class and solicited proposals for the first generation of Probes. With a larger cost cap, Probes can achieve more ambitious science than SMEXs or MIDEXs and be implemented faster than Flagships—as frequently as one per decade. The PRobe far-Infrared Mission for Astrophysics (PRIMA) is one of two Probe concepts selected by NASA for a concept study in 2024/2025, potentially leading to implementation and launch as early as 2031. PRIMA was designed for a broad range of astrophysics, from how planets assemble their atmospheres, to the coevolution of galaxies and black holes, to the evolving properties of dust and galactic metallicity over cosmic time. Seventy-five percent of PRIMA’s observing time will be allocated to guest observer observations and 25% allocated to principal investigator science; however, the principal investigator science data will be available promptly for guest investigator usage. The observatory features a 1.8-m diameter telescope cooled to 4.5 K with two science instruments: the Far-InfraRed Enhanced Survey Spectrometer (FIRESS) and the PRIMA imager (PRIMAger). FIRESS provides continuous spectral coverage from 24 to 235 μm, in two spectral resolution modes (R ≥ 85 and R ¼ 4400ð112 μm∕λÞ), with spectral mapping capability and order-of-magnitude sensitivity improvement over previous observatories. PRIMAger delivers similar sensitivity advances and first-of-its-kind far-infrared hyperspectral imaging for astrophysics with R ∼ 8 from 25 to 84 μm, and polarimetry in four broadband filters from 80 to 261 μm. PRIMA’s science and technical motivation is outlined, its overall architecture is described, and its cryogenic payload and instruments, including the kinetic inductance detector arrays, and operations and observing modes, are summarized.

The PRobe far-Infrared Mission for Astrophysics (PRIMA) is an infrared observatory for the next decade, currently in Phase A, with a 1.8 m telescope actively cooled to 4.5 K. On board, an infrared camera, PRIMAger, equipped with ultra-sensitive kinetic inductance detector arrays, will provide observers with a coverage of mid-infrared to far-infrared wavelengths from 24 to 264 μm. PRIMAger will offer two imaging modes: the hyperspectral mode will cover the 24 to 84 μm wavelength range with a spectral resolution R ≥ 8, whereas the polarimetric mode will provide polarimetric imaging in four broadbands from 80 to 264 μm. These observational capabilities have been tailored to answer fundamental astrophysical questions such as black hole and star-formation co-evolution in galaxies, the evolution of small dust grains over a wide range of redshifts, and the effects of interstellar magnetic fields in various environments, as well as to open a vast discovery space with versatile photometric and polarimetric capabilities. PRIMAger is being developed by an international collaboration bringing together French institutes (Laboratoire d’Astrophysique de Marseille and CEA) through the Center National d’Etudes Spatiales (CNES, Paris, France), the Netherlands Institute for Space Research (SRON, Leiden, Netherlands), and the Cardiff University (Cardiff, UK) in Europe, as well as the Jet Propulsion Laboratory and Goddard Space Flight Center in the United States.

The PRobe far-Infrared Mission for Astrophysics (PRIMA) is an astrophysics mission concept currently under study. The instrument comprises four focal plane arrays (FPAs), each with over 1000 pixels, consisting of lens-coupled kinetic inductance detectors designed for ultra-high sensitivity spectroscopy and imaging. PRIMA covers the far-infrared band from 24 to 250 μm. We present the fundamental properties of lens-coupled absorbers, including aperture efficiency, throughput, and beam patterns. Compared with bare absorbers, lens-coupled absorbers exhibit reduced sensitivity to noise from both the instrument enclosure and the sky background. We analyze FPA sampling strategies in terms of relative observing speed, considering both detector noise–limited and background noise–limited scenarios. In the background noise–limited case, near-maximum-gain sampling is optimal only when the point spread function (PSF) in the reflector focal plane is aligned with the lens. For arbitrary PSF incidence, a near-Nyquist sampling configuration provides the best average performance. These calculations are based on a computationally efficient quasi-analytical technique and assume a hex-packed array of circular lenses, recently developed for PRIMA.

Lens based Microwave Kinetic Inductance Detectors combined with distributed absorbers are one of the main candidates for large format, extremely sensitive detector systems for Far Infrared Astronomy. In this paper, the optimal design of integrated dielectric lenses, based on the response of the distributed absorber to incident plane waves, is studied. For the analysis, two efficiency terms are defined, namely spectral and spillover efficiencies, decomposing the effect of the absorber’s response to incident plane waves from that of its physical dimensions, on the total power captured by the detector system. Linearly polarized absorbers, made of Aluminium strips are considered as an indicative absorber geometry, with or without a quarter-wavelength backing reflector.

Achieving a wide instantaneous bandwidth and wide scanning capabilities are essential for development of (sub)millimeter imaging spectrometers for astronomical observations. Such an instrument can be realized using complex quasi-optical (QO) systems. In this work, we propose a QO architecture based on refractive components to reduce the overall size and volume of the instrument. This compact design is optimized using a sequential Geometrical Optics based technique. The performance of the preliminary design is reported in terms of the aperture efficiency over an octave of bandwidth and the field of view of the telescope hosting the instrument exhibiting less than 1dB of scan loss. The finalized design of the instrument, its performance, and realization approach will be discussed at the conference.

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Context. Integrated superconducting spectrometers (ISSs) for wide-band submillimeter (submm) astronomy use quasi-optical systems for coupling radiation from the telescope to the instrument. Misalignment in these systems is detrimental to the system performance. The common method of using an optical laser to align the quasi-optical components requires an accurate alignment of the laser to the submm beam from the instrument, which is not always guaranteed to a sufficient accuracy. Aims. We develop an alignment strategy for wide-band ISSs that directly uses the submm beam of the wide-band ISS. The strategy should be applicable in both telescope and laboratory environments. Moreover, the strategy should deliver similar quality of the alignment across the spectral range of the wide-band ISS. Methods. We measured the misalignment in a quasi-optical system operating at submm wavelengths using a novel phase and amplitude measurement scheme that is capable of simultaneously measuring the complex beam patterns of a direct-detecting ISS across a harmonic range of frequencies. The direct detection nature of the microwave kinetic inductance detectors in our device-under-test, DESHIMA 2.0, necessitates the use of this measurement scheme. Using geometrical optics, the measured misalignment, a mechanical hexapod, and an optimisation algorithm, we followed a numerical approach to optimise the positioning of corrective optics with respect to a given cost function. Laboratory measurements of the complex beam patterns were taken across a harmonic range between 205 and 391 GHz and were simulated through a model of the ASTE telescope in order to assess the performance of the optimisation at the ASTE telescope. Results. Laboratory measurements show that the optimised optical setup corrects for tilts and offsets of the submm beam. Moreover, we find that the simulated telescope aperture efficiency is increased across the frequency range of the ISS after the optimisation.

We report measurements characterizing the performance of a kinetic inductance detector array designed for a wavelength of 25 microns and very low optical background level suitable for applications such as a far-infrared instrument on a cryogenically cooled space telescope. In a pulse-counting mode of operation at low optical flux, the detectors can resolve individual 25-micron photons. In an integrating mode, the detectors remain photon noise limited over more than 6 orders of magnitude in absorbed power from 70 zW to 200 fW, with a limiting noise equivalent power of 4.6×10-20 W Hz-1 at 1 Hz. In addition, the detectors are highly stable with flat power spectra under optical load down to 1 mHz. Operational parameters of the detector are determined including the efficiency of conversion of the incident optical power into quasiparticles in the aluminum absorbing element and the quasiparticle self-recombination constant.

Parallel-plate capacitors (PPC) significantly reduce the size of superconducting microwave resonators, reducing the pixel pitch for arrays of single-photon energy-resolving kinetic inductance detectors (KIDs). The frequency noise of KIDs is typically limited by tunneling two-level systems (TLS), which originate from lattice defects in the dielectric materials required for PPCs. How the frequency noise level depends on the PPC's dimensions has not been experimentally addressed. We measure the frequency noise of 56 resonators with a-SiC:H PPCs, which cover a factor of 44 in PPC area and a factor of 4 in dielectric thickness. To support the noise analysis, we measure the resonators' TLS-induced power-dependent intrinsic loss and temperature-dependent resonance frequency shift. From the TLS models, we expect a geometry-independent microwave loss and resonance frequency shift, which is set by the TLS properties of the dielectric. However, we observe a thickness-dependent microwave loss and resonance frequency shift; this is explained by surface layers that limit the performance of PPC-based resonators. For a uniform dielectric, the frequency noise level should scale directly inversely with the PPC area and thickness. We observe that an increase in PPC size reduces the frequency noise, but the exact scaling is, in some cases, weaker than expected. Finally, we derive engineering guidelines for the design of KIDs based on PPC-based resonators.

Achieving amplification with high gain and quantum-limited noise is a difficult problem to solve. Parametric amplification using a superconducting transmission line with high kinetic inductance is a promising technology not only to solve this problem but also adding several benefits. Compared with other technologies, they have the potential to improve power saturation, achieve larger fractional bandwidths, and operate at higher frequencies. In this type of amplifier, the selection of the proper transmission line is a key element in its design. Given current fabrication limitations, traditional lines, such as coplanar waveguides (CPW), are not ideal for this purpose, since it is difficult to make them with the proper characteristic impedance for good matching and slow enough phase velocity for making them more compact. Capacitively loaded lines, also known as artificial lines, are a good solution to this problem. However, few design rules or models have been presented to guide their accurate design. This fact is even more crucial considering that they are usually fabricated in the form of Floquet lines that have to be designed carefully to suppress undesired harmonics appearing in the parametric process. In this article we present, first, a new modeling strategy, based on the use of electromagnetic-simulation software, and, second, a first-principles model that facilitate and speed the design of CPW artificial lines and of Floquet lines made out of them. Then, we present comparisons with experimental results that demonstrate their accuracy. Finally, the theoretical model allows one to predict the high-frequency behavior of the artificial lines, showing that they are good candidates for implementing parametric amplifiers above 100 GHz.

Many superconducting on-chip filter-banks suffer from poor coupling to the detectors behind each filter. This is a problem intrinsic to the commonly used half-wavelength filter, which has a maximum theoretical coupling of 50 %. In this paper, we introduce a phase-coherent filter, called a directional filter, which has a theoretical coupling of 100 %. In order to study and compare different types of filter-banks, we first analyze the measured filter frequency scatter, losses, and spectral resolution of a DESHIMA 2.0 filter-bank chip. Based on measured fabrication tolerances and losses, we adapt the input parameters for our circuit simulations, quantitatively reproducing the measurements. We find that the frequency scatter is caused by nanometer-scale line width variations and that variances in the spectral resolution is caused by losses in the dielectric only. Finally, we include these realistic parameters in a full filter-bank model and simulate a wide range of spectral resolutions and oversampling values. For all cases, the directional filter-bank has significantly higher coupling to the detectors than the half-wave resonator filter-bank. The directional filter eliminates the need to use oversampling as a method to improve the total efficiency, instead capturing nearly all the power remaining after dielectric losses.