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 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.
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