We present the design and testing of spaceflight multiplexing kinetic inductance detector (KID) readout electronics for the PRobe far-Infrared Mission for Astrophysics (PRIMA). PRIMA is a mission proposed to the 2023 NASA Astrophysics Probe Explorer (APEX) Announcement of Opportunity that will answer fundamental questions about the formation of planetary systems, as well as the formation and evolution of stars, supermassive black holes, and dust over cosmic time. The readout electronics for PRIMA must be compatible with operation at Earth-Sun L2 and capable of multiplexing more than 1000 detectors over 2 GHz bandwidth while consuming around 30 W per readout chain. The electronics must also be capable of switching between the two instruments, which have different readout bands,: the hyperspectral imager (PRIMAger, 2.5-5.0 GHz) and the spectrometer (FIRESS, 0.4-2.4 GHz). We present the driving requirements, design, and measured performance of a laboratory brassboard system.
We present the design and optical characterization of a novel highly compact three-dimensional microwave kinetic inductance detector (3D-MKID). At short wavelengths, such as the far- and mid-infrared, the pixel density of MKID arrays is often limited by the size and geometry of each resonator’s capacitor. Sending the non-optically active component of the resonator into the third dimension minimizes the footprint of each pixel, allowing much higher array densities to be achieved. In our 3D-MKID design, we compactify the resonator by conformally coating deep-etched holes in the silicon substrate with superconducting films formed by atomic layer deposition. The resulting geometry consists of three-dimensional coaxial transmission lines, which are then connected to a meandered absorber on the substrate surface. An array of these resonators are capacitively coupled to a microstrip feedline. We present the characterization of a prototype 3D-MKID array and compare it to simulate resonator properties. We additionally describe the detector sensitivity performance when illuminated by a far-infrared blackbody source.
The optical coupling of detectors to telescope optics is a challenge for future far-infrared astrophysics observatories. The PRobe far-Infrared Mission for Astrophysics (PRIMA) collaboration has developed monolithic silicon microlens arrays for superconducting detector arrays spanning wavelengths from 24 to 261 microns. These custom-microfabricated lens arrays meet the stringent surface accuracy and roughness requirements that are necessary at PRIMA’s shortest wavelengths. Grayscale lithography is used in combination with deep silicon plasma etching to create arrays of three-dimensional lens profiles. This fabrication process generates highly uniform and accurate microlenses across a roughly 80 by 10 millimeter 1008-element array. The kilopixel microlens arrays are bonded to matching PRIMA detector arrays with a thin and uniform layer of epoxy. In this presentation, we report on the status and performance of PRIMA’s microlens fabrication and microlens-detector array hybridization processes.
Proposed for a late 2031 launch, PRIMA, the Probe far-Infrared Mission for Astrophysics, closes the gap between JWST and ALMA, offering unprecedented sensitivity and spectroscopic mapping capability in the 24-264 μm range for detailed studies of galactic evolution, planetary atmospheres, and dust-metal dynamics. Onboard PRIMA, the PRIMAger camera operates in the 25-80 μm bands utilizing advanced MKID detector modules for hyperspectral imaging enabled by Linear Variable Filters. This paper presents a graded resonant metal-mesh filter technology, demonstrating very promising efficiency in the short wavelength range. Overcoming dielectric loss limitations, an innovative dual-layer LVF design on thin membranes achieves a transmission of 80-90% at 12 THz. Rigorous electromagnetic modeling, optimization, and position-dependent spectral response measurements validate the filter performance. We present a comprehensive set of simulation and experimental results, including environmental pre-qualification tests, strongly supporting the suitability of this technology for future space applications.
The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a balloon-borne telescope designed to survey star formation over cosmological time scales using intensity mapping in the 420 – 540 GHz frequency range. EXCLAIM uses a fully cryogenic telescope coupled to six on-chip spectrometers featuring kinetic inductance detectors (KIDs) to achieve high sensitivity, allowing for fast integration in dark atmospheric windows. The telescope receiver is cooled to ≈ 1.7 K by immersion in a superfluid helium bath and enclosed in a superfluid-tight shell with a meta-material anti-reflection coated silicon window. In addition to the optics and the spectrometer package, the receiver contains the magnetic shielding, the cryogenic segment of the spectrometer readout, and the sub-Kelvin cooling system. A three-stage continuous adiabatic demagnetization refrigerator (CADR) keeps the detectors at 100 mK while a 4He sorption cooler provides a 900 mK thermal intercept for mechanical suspensions and coaxial cables. We present the design of the EXCLAIM receiver and report on the flight-like testing of major receiver components, including the superfluid-tight receiver window and the sub-Kelvin coolers.
We have obtained NASA funding to build and demonstrate Transition Edge Sensor (TES) based kilopixel arrays with the properties that match the requirements for cryogenic far-infrared space missions: the arrays are very closely tileable in one direction and have only a moderate gap in the other direction. This array architecture can meet the sampling- and pixel number requirement of ~ 104 pixels. Many details of the architecture have already been demonstrated individually, and the detector board will be optimized for the use of the latest cryogenic bump bonded NIST 2-D time domain SQUID readout multiplexers with a high density fanout scheme. Additionally, we use flex-lines that are very similar to those developed at Princeton University for the ACT project. We already have a pixel design that exceeds the continuum sensitivity requirements for a cryogenic space mission.
The PRobe far-Infrared Mission for Astrophysics (PRIMA) is a future cryogenic space observatory that will revolutionize study of evolving galaxies and forming planetary systems with highly-sensitive far-infrared (far-IR) imaging and spectroscopy. PRIMA’s spectrometer, the Far-InfraRed Enhanced Survey Spectrometer (FIRESS), will deploy kilo-pixel aluminum kinetic inductance detector (KID) arrays covering wavelengths from 24-235 μm. Here we present optical characterization of a prototype FIRESS array operating at 25 μm. We employ a blackbody modulation technique to measure the detector responsivity, and discuss methods for reducing 1/f noise from the multi-tone readout electronics. We measure an NEP below 3.5 × 10−20 W/ √ Hz at 10 Hz accross the array, which exceeds the requirement to be limited by the astrophysical background limit for PRIMA’s FIRESS spectrometer. We discuss limitations of the multi-tone readout and compare results to measurements with a single-tone readout system.
We present a characterization of the mapping from resonant frequency to spatial position for a kilopixel kinetic inductance detector (KID) array developed for the Probe far-Infrared Mission for Astrophysics (PRIMA). This work targets the longest wavelength band of PRIMA’s FIRESS spectrometer, which in total spans 24 to 235 μm. Light emitting diodes arrayed to match repeating unit cells of 16 KIDs first discriminate among unit cells. Within each unit cell, frequencies are widely spaced, so positions are discriminated by theoretical predictions of the relative frequency spacing between detectors based on KID geometries. With this mapping, we analyze board features to improve the accuracy of modeling PRIMA KIDs and inform future fabrication runs.
The Probe far-Infrared Mission for Astrophysics (PRIMA) is a proposed space observatory which will use arrays of thousands of kinetic inductance detectors (KIDs) to perform low- and moderate-resolution spectroscopy throughout the far-infrared. The detectors must have noise equivalent powers (NEPs) at or below 1×10−19 W Hz−1/2 to be subdominant to noise from sky backgrounds and thermal noise from PRIMA’s cryogenically cooled primary mirror. Using a Radio Frequency System on a Chip for multitone readout, we measure the NEPs of detectors on a flight-like array designed to observe at a wavelength of 210 μm. We find that 92% of the KIDs measured have an NEP below 1 × 10−19 W Hz−1/2 at a noise frequency of 10 Hz.
The far-infrared (IR) region is rich with information needed to characterize interstellar dust and to investigate the cold outer planets of the solar system and their icy moons. The proposed sub-orbital observatory the balloon experiment for galactic infrared science (BEGINS) will utilize cryogenic instruments to map spectral energy distributions (SEDs) of interstellar dust in the Cygnus molecular cloud complex. A future high priority flagship mission Uranus Orbiter and Probe carrying a net flux radiometer (NFR) will study the in situ heat flux of the icy giants atmosphere to 10 bar pressure. These instruments require far-IR filters to define the instrument spectral bandwidths. Our ultimate goal is to define the instrument bands of BEGINS and the NFR with linear-variable filters (LVFs) and discrete-variable filters (DVFs). The LVFs and DVFs will be made of metal mesh band-pass filters (MMBF) comprised of a 100 nm thick gold film with cross-shaped slots of varying sizes along a silicon (Si) substrate with cyclic olefin copolymer (COC) anti-reflection (AR) coatings. We present our progress towards LVFs and DVFs with simulated and measured transmission of a room temperature, non-AR coated, single-band 44 µm MMBF filter. We have successfully fabricated, measured, and modeled a non-AR coated, room temperature 44 µm MMBF. The transmission at room temperature and non-AR coated was measured to be 27% with a resolving power of 11. When COC-AR coated on both sides the transmission is expected to increase to 69% with a resolving power of ten.
The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) will constrain star formation over cosmic time by carrying out a blind and complete census of redshifted carbon monoxide (CO) and ionized carbon ([CII]) emission in cross-correlation with galaxy survey data in redshift windows from the present to z=3.5 with a fully cryogenic, balloon-borne telescope. EXCLAIM will carry out extragalactic and Galactic surveys in a conventional balloon flight planned for 2023. EXCLAIM will be the first instrument to deploy µ-Spec silicon integrated spectrometers with a spectral resolving power R=512 covering 420-540 GHz. We summarize the design, science goals, and status of EXCLAIM.
With the recent Astro2020 report, a NASA-led cryogenic far-IR probe has emerged as the primary opportunity for sensitive measurements between the 28-micron cutoff of JWST and the onset of ground-based windows in the submillimeter. The probe will provide new tools for topics ranging from star formation in the earliest galaxies, to the cosmic history of heavy elements, to the formation of stars and planets. We will present our work optimizing the scientific return from this powerful yet cost-capped mission. The instrumentation emphasizes spectrophotometry and spectroscopy, both wide-field and pointed. It will provide high-fidelity maps and unbiased redshift-resolved surveys, as well as rich, high-sensitivity spectra of targets of interest. Paramount among the design trades is that of spatial multiplexing vs spectral resolving power; this optimization is conducted in light of the multiple science goals, and within the constraints of realistic detector sensitivity and array format.
The current state of far-infrared astronomy drives the need to develop compact, sensitive spectrometers for future space and ground-based instruments. Here we present details of the μ-Spec spectrometers currently in development for the far-infrared balloon mission EXCLAIM. The spectrometers are designed to cover the 555 – 714 μm range with a resolution of R = λ/Δλ = 512 at the 638 μm band center. The spectrometer design incorporates a Rowland grating spectrometer implemented in a parallel plate waveguide on a low-loss single-crystal Si chip, employing Nb microstrip planar transmission lines and thin-film Al kinetic inductance detectors (KIDs). The EXCLAIM μ-Spec design is an advancement upon a successful R = 64 μ-Spec prototype, and can be considered a sub-mm superconducting photonic integrated circuit (PIC) that combines spectral dispersion and detection. The design operates in a single M=2 grating order, allowing one spectrometer to cover the full EXCLAIM band without requiring a multi-order focal plane. The EXCLAIM instrument will fly six spectrometers, which are fabricated on a single 150 mm diameter Si wafer. Fabrication involves a flipwafer-bonding process with patterning of the superconducting layers on both sides of the Si dielectric. The spectrometers are designed to operate at 100 mK, and will include 355 Al KID detectors targeting a goal of NEP ∼8 × 10−19 W/√ Hz. We summarize the design, fabrication, and ongoing development of these μ-Spec spectrometers for EXCLAIM.
The experiment for cryogenic large-aperture intensity mapping (EXCLAIM) is a balloon-borne telescope designed to survey star formation in windows from the present to z = 3.5. During this time, the rate of star formation dropped dramatically, while dark matter continued to cluster. EXCLAIM maps the redshifted emission of singly ionized carbon lines and carbon monoxide using intensity mapping, which permits a blind and complete survey of emitting gas through statistics of cumulative brightness fluctuations. EXCLAIM achieves high sensitivity using a cryogenic telescope coupled to six integrated spectrometers employing kinetic inductance detectors covering 420 to 540 GHz with spectral resolving power R = 512 and angular resolution ≈4 arc min. The spectral resolving power and cryogenic telescope allow the survey to access dark windows in the spectrum of emission from the upper atmosphere. EXCLAIM will survey 305 deg2 in the Sloan Digital Sky Survey Stripe 82 field from a conventional balloon flight in 2023. EXCLAIM will also map several galactic fields to study carbon monoxide and neutral carbon emission as tracers of molecular gas. We summarize the design phase of the mission.
The Galaxy Evolution Probe (GEP) is a concept for a mid- and far-infrared space observatory to measure key properties of large samples of galaxies with large and unbiased surveys. GEP will attempt to achieve zodiacal light and Galactic dust emission photon background-limited observations by utilizing a 6-K, 2.0-m primary mirror and sensitive arrays of kinetic inductance detectors (KIDs). It will have two instrument modules: a 10 to 400 μm hyperspectral imager with spectral resolution R = λ / Δλ ≥ 8 (GEP-I) and a 24 to 193 μm, R = 200 grating spectrometer (GEP-S). GEP-I surveys will identify star-forming galaxies via their thermal dust emission and simultaneously measure redshifts using polycyclic aromatic hydrocarbon emission lines. Galaxy luminosities derived from star formation and nuclear supermassive black hole accretion will be measured for each source, enabling the cosmic star formation history to be measured to much greater precision than previously possible. Using optically thin far-infrared fine-structure lines, surveys with GEP-S will measure the growth of metallicity in the hearts of galaxies over cosmic time and extraplanar gas will be mapped in spiral galaxies in the local universe to investigate feedback processes. The science case and mission architecture designed to meet the science requirements is described, and the KID and readout electronics state of the art and needed developments are described. This paper supersedes the GEP concept study report cited in it by providing new content, including: a summary of recent mid-infrared KID development, a discussion of microlens array fabrication for mid-infrared KIDs, and additional context for galaxy surveys. The reader interested in more technical details may want to consult the concept study report.
The Origins Space Telescope (Origins) will have a 5.9-m diameter primary mirror cooled to 4.5 K and will be equipped with three instruments, two of which will cover the far-IR (λ = 25 to 588 μm). These far-IR instruments will require large arrays (∼104 detectors) of ultrasensitive detectors, with noise equivalent powers (NEPs) as low as 3 × 10 − 20 W Hz − 1/2. Kinetic inductance detectors (KIDs) have already demonstrated the array format, modularity, and readout multiplexing density requirements for Origins; the only aspect that requires improvement is the per-pixel sensitivity. We show how KIDs can meet the sensitivity target, focusing on two existing architectures that together demonstrate the key necessary attributes. Arrays of antenna-coupled coplanar waveguide resonators have achieved NEPs of 3 × 10 − 19 W Hz − 1/2 in laboratory demonstrations at 350 μm; they demonstrate excellent material properties as well as array-level integration and performance. Lumped element detectors such as those under development for balloon-borne spectroscopy at 10 to 350 μm demonstrate flexibility in coupling to shorter-wavelengths, reducing active volume, and providing a means for suppressing capacitor noise. A straightforward combination of the elements of these already-demonstrated devices points to a low-volume design that is expected to meet the Origins sensitivity targets.
The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a balloon-borne far-infrared telescope that will survey galactic formation history over cosmological time scales with redshifts between 0 and 3.5. EXCLAIM will measure the statistics of brightness fluctuations of redshifted cumulative carbon monoxide and singly ionized carbon line emissions, following an intensity mapping approach. EXCLAIM will couple all-cryogenic optical elements to six μ-Spec spectrometer modules, operating at 420-540 GHz with a spectral resolution of 512 and featuring microwave kinetic inductance detectors. Here, we present an overview of the mission and its development status.
This work describes the optical design of the EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM). EXCLAIM is a balloon-borne telescope that will measure integrated line emission from carbon monoxide (CO) at redshifts z<1 and ionized carbon ([CII]) at redshifts z = 2.5-3.5 to probe star formation over cosmic time in cross-correlation with galaxy redshift surveys. The EXCLAIM instrument will observe at frequencies of 420--540 GHz using six microfabricated silicon integrated spectrometers with spectral resolving power R = 512 coupled to kinetic inductance detectors (KIDs). A completely cryogenic telescope cooled to a temperature below 5 K provides low-background observations between narrow atmospheric lines in the stratosphere. Off-axis reflective optics use a 90-cm primary mirror to provide 4.2' full-width at half-maximum (FWHM) resolution at the center of the EXCLAIM band over a field of view of 22.5'.
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