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Register a new userMicrofabrication technology for large LEKID arrays : from NIKA2 to future applications
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The Lumped Element Kinetic Inductance Detectors (LEKID)demonstrated full maturity in the NIKA (New IRAM KID Arrays)instrument. These results allow directly comparing LEKID performance with other competing technologies (TES, doped silicon) in the mm and sub-mm range. A continuing effort is ongoing to improve the microfabrication technologies and concepts in order to satisfy the requirements of new instruments. More precisely, future satellites dedicated to CMB (Cosmic Microwave Background) studies will require the same focal plane technology to cover, at least, the frequency range of 60 to 600 GHz. Aluminium LEKID developed for NIKA have so far demonstrated, under real telescope conditions, performance approaching photon-noise limitation in the band 120-300 GHz. By implementing superconducting bi-layers we recently demonstrated LEKID arrays working in the range 80-120 GHz and with sensitivities approaching the goals for CMB missions. NIKA itself (350 pixels) is followed by a more ambitious project requiring several thousands (3000-5000) pixels. NIKA2 has been installed in October 2015 at the IRAM 30-m telescope. We will describe in detail the technological improvements that allowed a relatively harmless 10-fold up-scaling in pixels count without degrading the initial sensitivity. In particular we will briefly describe a solution to simplify the difficult fabrication step linked to the slot-line propagation mode in coplanar waveguide.
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We report the design, fabrication and testing of Lumped Element Kinetic Inductance Detectors (LEKID) showing performance in line with the requirements of the next generation space telescopes operating in the spectral range from 80 to 600 GHz. This range is of particular interest for Cosmic Microwave Background (CMB) studies. For this purpose we have designed and fabricated 100-pixel arrays covering five distinct bands. These wafers have been measured via multiplexing, where a full array is read out using a single pair of lines. We adopted a custom cold black-body installed in front of the detectors and regulated at temperatures between 1 K and 20 K. We will describe in the present paper the main design considerations, the fabrication processes, the testing and the data analysis.
We discuss the design and measured performance of a titanium nitride (TiN) mesh absorber we are developing for controlling optical crosstalk in horn-coupled lumped-element kinetic inductance detector arrays for millimeter-wavelengths. This absorber was added to the fused silica anti-reflection coating attached to previously-characterized, 20-element prototype arrays of LEKIDs fabricated from thin-film aluminum on silicon substrates. To test the TiN crosstalk absorber, we compared the measured response and noise properties of LEKID arrays with and without the TiN mesh. For this test, the LEKIDs were illuminated with an adjustable, incoherent electronic millimeter-wave source. Our measurements show that the optical crosstalk in the LEKID array with the TiN absorber is reduced by 66% on average, so the approach is effective and a viable candidate for future kilo-pixel arrays.
This document summarizes how far the Nancy Grace Roman Space Telescope Coronagraph Instrument (Roman CGI) will go toward demonstrating high-contrast imaging and spectroscopic requirements for potential future exoplanet direct imaging missions, illustrated by the HabEx and LUVOIR concepts. The assessment is made for two levels of assumed CGI performance: (i) current best estimate (CBE) as of August 2020, based on laboratory results and realistic end-to-end simulations with JPL-standard Model Uncertainty Factors (MUFs); (ii) CGI design specifications inherited from Phase B requirements. We find that the predicted performance (CBE) of many CGI subsystems compares favorably with the needs of future missions, despite providing more modest point source detection limits than future missions. This is essentially due to the challenging pupil of the Roman Space Telescope; this pupil pushes the coronagraph masks sensitivities to misalignments to be commensurate with future missions. In particular, CGI will demonstrate active low-order wavefront control and photon counting capabilities at levels of performance either higher than, or comparable to, the needs of future missions.
The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a set of mission concepts for the next generation of UVOIR space observatory with a primary aperture diameter in the 8-m to 16-m range that will allow us to perform some of the most challenging observations to answer some of our most compelling questions, including Is there life elsewhere in the Galaxy? We have identified two different telescope architectures, but with similar optical designs, that span the range in viable technologies. The architectures are a telescope with a monolithic primary mirror and two variations of a telescope with a large segmented primary mirror. This approach provides us with several pathways to realizing the mission, which will be narrowed to one as our technology development progresses. The concepts invoke heritage from HST and JWST design, but also take significant departures from these designs to minimize complexity, mass, or both. Our report provides details on the mission concepts, shows the extraordinary scientific progress they would enable, and describes the most important technology development items. These are the mirrors, the detectors, and the high-contrast imaging technologies, whether internal to the observatory, or using an external occulter. Experience with JWST has shown that determined competitors, motivated by the development contracts and flight opportunities of the new observatory, are capable of achieving huge advances in technical and operational performance while keeping construction costs on the same scale as prior great observatories.
Optical fibers have altered astronomical instrument design by allowing for a complex, often large instrument to be mounted in a remote and stable location with respect to the telescope. The fibers also enable the possibility to rearrange the signal from a focal plane to form a psuedo-slit at the entrance to a spectrograph, optimizing the detector usage and enabling the study of hundreds of thousands of stars or galaxies simultaneously. Multi-core fibers in particular offer several favorable properties with respect to traditional fibers: 1) the separation between single-mode cores is greatly reduced and highly regular with respect to free standing fibers, 2) they offer a monolithic package with multi-fiber capabilities and 3) they operate at the diffraction limit. These properties have enabled the realization of single component photonic lanterns, highly simplified fiber Bragg gratings, and advanced fiber mode scramblers. In addition, the precise grid of cores has enabled the design of efficient single-mode fiber integral field units for spectroscopy. In this paper, we provide an overview of the broad range of applications enabled by multi-core fiber technology in astronomy and outline future areas of development.
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