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.
NASA’s Multi-Angle Imager for Aerosols (MAIA) mission, under development at the Jet Propulsion Laboratory, is designed to study the adverse health effects of different types of particulate air pollution. Planned for launch in late 2022 for a 3-year mission, the MAIA satellite instrument will focus on a selected set of metropolitan target areas, where air quality monitors and health data are available. Aerosol concentration and speciation are inferred from multi-angle measurements of backscattered sunlight in 14 spectral bands from 350-2200 nm, with bands near 442, 645 and 1040 nm measuring the degree (DoLP) and angle of linear polarization (AoLP) in addition to radiance. The pushbroom camera has a ~240-km cross-track field of view with a nadir resolution of ~200 m, and is mounted onto a biaxial gimbal to provide along-track view angles within ±60°, to extend the field of regard to ±48°, and to view the instrument’s onboard calibrator (OBC) and dark target. The OBC consists of a sunlit transmissive diffuser, followed by 12 polarizers at different orientations. MAIA’s polarimetry is implemented using miniature wiregrid polarizers on the focal plane array, and dual photoelastic modulators (PEMs) and achromatic quarter-wave plates to rapidly rotate the polarization. The resulting ~26-Hz intensity modulation encodes the linearly polarized and total radiance in each pixel, leaving the DoLP and AoLP insensitive to gain calibration. We report on the polarimetric calibration of the MAIA camera using a vacuum-compatible polarization state generator, consisting of a 1600W Xenon lamp, 12-inch integrating sphere, and rotating high-extinction polarizer. Mueller-matrix-based calibration coefficients for each detector pixel are derived from measurements at multiple polarizer angles, and are used to correct the measurements for instrumental polarization aberrations. Prior to flight, the calibrated MAIA camera is panned across the OBC to characterize its output, using uniform illumination with an irradiance similar to the Sun.
Compact, room temperature terahertz sources are much needed in the 1 to 3 THz band for developing multi-pixel heterodyne receivers for astrophysics and planetary science or for building short-range high spatial resolution THz imaging systems able to see through low water content and non metallic materials, smoke or dust for a variety of applications ranging from the inspection of art artifacts to the detection of masked or concealed objects. All solid-sate electronic sources based on a W-band synthesizer followed by a high-power W-band amplifier and a cascade of Schottky diode based THz frequency multipliers are now capable of producing more than 1 mW at 0.9THz, 50 μW at 2 THz and 18 μW at 2.6 THz without the need of any cryogenic system. These sources are frequency agile and have a relative bandwidth of 10 to 15%, limited by the high power W-band amplifiers. The paper will present the latest developments of this technology and its perspective in terms of frequency range, bandwidth and power.
7010-5Thijs de Graauw, Nick Whyborn, Frank Helmich, Pieter Dieleman, Peter Roelfsema, Emmanuel Caux, Tom Phillips, Jürgen Stutzki, Douwe Beintema, Arnold Benz, Nicolas Biver, Adwin Boogert, Francois Boulanger, Sergey Cherednichenko, Odile Coeur-Joly, Claudia Comito, Emmanuel Dartois, Albrecht de Jonge, Gert de Lange, Ian Delorme, Anna DiGiorgio, Luc Dubbeldam, Kevin Edwards, Michael Fich, Rolf Güsten, Fabrice Herpin, Netty Honingh, Robert Huisman, Herman Jacobs, Willem Jellema, Jon Kawamura, Do Kester, Teun Klapwijk, Thomas Klein, Jacob Kooi, Jean-Michel Krieg, Carsten Kramer, Bob Kruizenga, Wouter Laauwen, Bengt Larsson, Christian Leinz, Rene Liseau, Steve Lord, Willem Luinge, Anthony Marston, Harald Merkel, Rafael Moreno, Patrick Morris, Anthony Murphy, Albert Naber, Pere Planesas, Jesus Martin-Pintado, Micheal Olberg, Piotr Orleanski, Volker Ossenkopf, John Pearson, Michel Perault, Sabine Phillip, Mirek Rataj, Laurent Ravera, Paolo Saraceno, Rudolf Schieder, Frank Schmuelling, Ryszard Szczerba, Russell Shipman, David Teyssier, Charlotte Vastel, Huib Visser, Klaas Wildeman, Kees Wafelbakker, John Ward, Roonan Higgins, Henri Aarts, Xander Tielens, Peer Zaal
This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI), to be launched onboard of ESA's Herschel Space Observatory, by 2008. It includes the first results from the instrument level tests. The instrument is designed to be electronically tuneable over a wide and continuous frequency range in the Far Infrared, with velocity resolutions better than 0.1 km/s with a high sensitivity. This will enable detailed investigations of a wide variety of astronomical sources, ranging from solar system objects, star formation regions to nuclei of galaxies.
The instrument comprises 5 frequency bands covering 480-1150 GHz with SIS mixers and a sixth dual frequency band, for the 1410-1910 GHz range, with Hot Electron Bolometer Mixers (HEB). The Local Oscillator (LO) subsystem consists of a dedicated Ka-band synthesizer followed by 7 times 2 chains of frequency multipliers, 2 chains for each frequency band. A pair of Auto-Correlators and a pair of Acousto-Optic spectrometers process the two IF signals from the dual-polarization front-ends to provide instantaneous frequency coverage of 4 GHz, with a set of resolutions (140 kHz to 1 MHz), better than < 0.1 km/s. After a successful qualification program, the flight instrument was delivered and entered the testing phase at satellite level. We will also report on the pre-flight test and calibration results together with the expected in-flight performance.
The Submillimeter Probe of the Evolution of Cosmic Structure (SPECS) is a space-based imaging and spectral ("double Fourier") interferometer with kilometer maximum baseline lengths for imaging. This NASA "vision mission" will provide spatial resolution in the far-IR and submillimeter spectral range comparable to that of the Hubble Space Telescope, enabling astrophysicists to extend the legacy of current and planned far-IR observatories. The astrophysical information uniquely available with SPECS and its pathfinder mission SPIRIT will be briefly described, but that is more the focus of a companion paper in the Proceedings of the Optical, Infrared, and Millimeter Space Telescopes conference. Here we present an updated design concept for SPECS and for the pathfinder interferometer SPIRIT (Space Infrared Interferometric Telescope) and focus on the engineering and technology requirements for far-IR double Fourier interferometry. We compare the SPECS optical system requirements with those of existing ground-based and other planned space-based interferometers, such as SIM and TPF-I/Darwin.
Ultimately, after the Single Aperture Far-IR (SAFIR) telescope, astrophysicists will need a far-IR observatory that provides angular resolution comparable to that of the Hubble Space Telescope. At such resolution galaxies at high redshift, protostars, and nascent planetary systems will be resolved, and theoretical models for galaxy, star, and planet formation and evolution can be subjected to important observational tests. This paper updates information provided in a 2000 SPIE paper on the scientific motivation and design concepts for interferometric missions SPIRIT (the Space Infrared Interferometric Telescope) and SPECS (the Submillimeter Probe of the Evolution of Cosmic Structure). SPECS is a kilometer baseline far-IR/submillimeter imaging and spectral interferometer that depends on formation flying, and SPIRIT is a highly-capable pathfinder interferometer on a boom with a maximum baseline in the 30 - 50 m range. We describe recent community planning activities, remind readers of the scientific rationale for space-based far-infrared imaging interferometry, present updated design concepts for the SPIRIT and SPECS missions, and describe the main issues currently under study. The engineering and technology requirements for SPIRIT and SPECS, additional design details, recent technology developments, and technology roadmaps are given in a companion paper in the Proceedings of the conference on New Frontiers in Stellar Interferometry.
The Heterodyne Instrument for Far Infrared (HIFI) on ESA's Herschel Space Observatory utilizes a variety of novel RF components in its five SIS receiver channels covering 480- 1250 GHz and two HEB receiver channels covering 1410-1910 GHz. The local oscillator unit will be passively cooled while the focal plane unit is cooled by superfluid helium and cold helium vapors. HIFI employs W-band GaAs amplifiers, InP HEMT low noise IF amplifiers, fixed tuned broadband planar diode multipliers, high power W-band Isolators, and novel material systems in the SIS mixers. The National Aeronautics and Space Administration through the Jet Propulsion Laboratory is managing the development of the highest frequency (1119-1250 GHz) SIS mixers, the local oscillators for the three highest frequency receivers as well as W-band power amplifiers, high power W-band isolators, varactor diode devices for all high frequency multipliers and InP HEMT components for all the receiver channels intermediate frequency amplifiers. The NASA developed components represent a significant advancement in the available performance. This paper presents an update of the performance and the current state of development.
The Heterodyne Instrument for Far Infrared (HIFI) on ESA's Herschel Space Observatory is comprised of five SIS receiver channels covering 480-1250 GHz and two HEB receiver channels covering 1410-1910 GHz. Two fixed tuned local oscillator sub-bands are derived from a common synthesizer to provide the front-end frequency coverage for each channel. The local oscillator unti will be passively cooled while the focal plane unit is cooled by superfluid helium and cold helium vapors. HIFI employs W-band GaAs amplifiers, InP HEMT low noise IF amplifiers, fixed tuned broadband planar diode multipliers, and novel material systems in the SIS mixtures. The National Aeronautics and Space Administration's Jet Propulsion Laboratory is managing the development of the highest frequency (1119-1250 GHz) SIS mixers, the highest frequency (1650-1910 GHz) HEB mixers, local oscillators for the three highest frequency receivers as well as W-band power amplifiers, varactor diode devices for all high frequency multipliers and InP HEMT components for all the receiver channels intermediate frequency amplifiers. The NASA developed components represent a significant advancement in the available performance. The current state of the art for each of these devices is presented along with a programmatic view of the development effort.
Broadband fixed-tuned frequency multipliers in conjunction with broadband power amplifiers driven by frequency synthesizers are often used as local oscillator (LO) sources in the millimeter and submillimeter wave heterodyne instruments. At these frequencies the multipliers use Gallium Arsenide (GaAs) based Schottky varactor diodes as the nonlinear element, and like most other harmonic generators are susceptible to spurious signal interference. The state-of-the-art LO sources in the millimeter and submillimeter wavelengths use MMIC power amplifiers producing in excess of 250 mW of output power in the 100 GHz range, and they are used to drive the subsequent multiplier stages. Because of the high input power environment and the presence of noise in the system, the multipliers become vulnerable to spurious signal interference, either through the bias lines or through the RF port. As the spurious signals propagate through the multiplier chain, they generate inter-modulation products which might fall in the passband of the heterodyne instrument and seriously degrade its performance. The issues of frequency multiplier response to spurious signal interference and its effect on local oscillator performance in millimeter and submillimeter wave heterodyne instruments are investigated. Results of numerical harmonic balance simulations and laboratory experiments are presented here, and are found to show good agreement.
The Herschel Space Observatory (HSO), an ESA cornerstone mission with NASA contribution, will enable a comprehensive study of the galactic and the extra galactic universe. At the heart of this exploration are ultra sensitive coherent detectors for high-resolution spectroscopy. Successful operation of these receivers is predicated on providing a sufficiently powerful local oscillator (LO) source. Historically, a versatile space qualified LO source for frequencies beyond 500 GHz has been difficult if not impossible. This paper will focus on the effort under way to develop, build, characterize and qualify a LO chain to 1200 GHz (Band 5 on HSO) that is based on planar GaAs diodes mounted in waveguide circuits. State-of-the-art performance has been obtained from a three-stage (×2×2×3) multiplier chain that can provide a peak output power of 120 μW (1178 GHz) at room temperature and a peak output power of 190 μW at 1183 GHZ when cooled to 113 K. Implementation of this LO source for the Heterodyne Instrument for Far Infrared (HIFI) one of three instruments on HSO will be discussed in detail.
The development of widely tunable coherent frequency sources for application as local oscillators or simply as test equipment above 1 THz remains an impediment in receiver development and characterization. Photomixer sources have demonstrated sufficient power to pump SIS mixers to over 600 GHz and have demonstrated over 2.5 THz of bandwidth in a single device. First generation photomixer system solved the problem of frequency calibration, but failed to fully address the needed spectral purity required for heterodyne applications. A number of improved laser technologies are greatly simplifying the implementation and improving the spectral purity of photomixer systems, however a full system demonstration in the THz frequency range remains elusive. The current state of the art for photomixer based sources is explored in light of heterodyne local oscillator and coherent tests sources for antenna and component characterization at THz frequencies.
This paper summarizes the development of W Band amplifiers for the Local Oscillator (LO) chains for the Herschel HIFI (Heterodyne Instrument for Far Infrared) Instrument. Key amplifier development issues and their solutions are presented, which have been applied on the way to realizing stable, wide-band amplifiers capable of producing 240 mW or greater RF power output across the 71 to 106 GHz frequency range. The HIFI power amplifier design embodiment is based on an A-40 silicon-aluminum alloy package with six GaAs(Gallium Arsenide) HEMT(High Electron Mobility Transistors) MMIC(Monolithic Microwave Integrated Circuit) amplifier chips used in each amplifier. Development challenges addressed include: MMIC chip designs which initially had a variety of oscillation or "moding" propensities (mostly out-fo-band), signal splitter and combiner development and matching across the band, matching of chip characteristics for those chips installed in the parallel power combined arms of the amplifier, power output control and leveling. The chosen design solutions are presented, including device, component and material selection for amplifier operation at cryogenic temperatures. Room temperature and cryogenic (120 Kelvin) data is also shown for the amplifier.
The Heterodyne Instrument for FIRST (HIFI) is a heterodyne receiver system which has an intermediate frequency (IF) amplifier that will likely exhibit 1/f-type gain fluctuations. Although the level of fluctuation is very small, wideband spectral observations require exceptional stability. A methodology for measuring 1/f fluctuations is described along with measurements of two amplifiers. Comparisons are made with previous 1/f measurements of HEMT amplifiers. The implications for HIFI are described.
The Heterodyne Instrument for FIRST is comprised of five SIS receiver channels covering 480 - 1250 GHz and two HEB receiver channels covering parts of 1410 - 1910 GHz and 2400 - 2700 GHz. Two local oscillator sub-bands derived from a common synthesizer will pump each receiver band. The synthesizer, control electronics and frequency distribution will be performed in the spacecraft service module. The service module will be connected in the local oscillator unit on the outside of the cryostat with a WR-28 waveguide for each of the 14 local oscillator sub-bands. the local oscillator unit will be passively cooled and thermally isolated from the cryostat wall. The module is comprised of seven units, one for each receiver band, containing two multiplier chains consisting of a k- to w-band multiplier, a MMIC power amplifier operating in one of five bands between 71 and 113 GHz, the high frequency multipliers, launching optics and electrical distribution. The entire assembly will be cooled to 120 K. The local oscillator system has the two field technical challenge of providing broad band frequency coverage at very high frequencies. This will be achieved through the use of high power GaAs MMIC amplifiers and planar diode multiplier technology in a passively cooled 120 Kelvin environment. The design criteria and the resulting overall system design will be presented along with a programmatic view of the development program and development progress.
Several astrophysics and Earth observation space missions planned for the near future will require submillimeter-wave heterodyne radiometers for spectral line observations. One of these, the Far InfraRed and Submillimeter Telescope will perform high-sensitivity, high-resolution spectroscopy in the 400 to 2700 GHz range with a seven channel super- conducting heterodyne receiver complement. The local oscillators for all these channels will be constructed around state-of-the-art GaAs power amplifiers in the 71 to 115 GHz range, followed by planar Schottky diode multiplier chains. The Jet Propulsion Laboratory is responsible for developing the multiplier chains for the 1.2, 1.7, and 2.7 THz bands. This paper will focus on the designs and technologies being developed to enhance the current state- of-the-art, which is based on discrete planar or whisker contacted GaAs Schottky diode chips mounted in waveguide blocks. We are proposing a number of new planar integrated circuit and device topologies to implement multipliers at these high frequencies. Approaches include substrateless, framed and frameless GaAs membrane circuitry with single, and multiple planar integrated Schottky diodes. Circuits discussed include 200 and 400 GHz doublers, a 1.2 THz tripler and a 2.4 THz doubler. Progress to date, with the implications of this technology development for future Earth and space science instruments, is presented.
The Submillimeter Astronomy Investigation of Line Spectra is a balloon-borne experiment under study for a 100 day ultra- long duration balloon mission. The experiment would survey the galactic plane with 1 arc minute angular resolution and 1 km/sec velocity resolution in the important submillimeter lines of CII, NII, and OI. These tracers provide the structure and energetics of major components of the interstellar medium. This knowledge is crucial for understanding the life cycle of the Galactic gas and the processes of star formation and galactic evolution. This instrument's survey of large regions of the galactic plane complements both FIRST and SOFIA which will excel at pointed observations with higher angular resolution and broader spectral coverage. Details of the instrument design and observing strategy are presented.
FIRST (Far InfraRed and Submillimeter Telescope) is a European science mission that will perform photometry and spectroscopy in the 80 - 670 micrometers range. The proposed heterodyne instrument for FIRST is a seven-channel receiver, which combines the high spectral resolving capability (0.3 - 300 km/s) of the radio heterodyne technique with the low noise detection offered by superconductor-insulator- superconductor and hot electron bolometer mixers. It is designed to provide almost continuous frequency coverage from 480 - 2700 GHz. The Jet Propulsion Laboratory is responsible for developing and implementing the local oscillator sources for the 1200 - 2700 GHz mixers. The present state-of-the-art approach for millimeter-wave multipliers, based on waveguide blocks and discretely mounted devices, becomes harder and harder to implement as the frequency range is extended beyond 300 GHz. This talk will focus on the technology that is being developed to enhance and extend planar integrated Schottky devices and circuits to meet mission local oscillator requirements. The baseline approach is to use GaAs power amplifiers from 71 to 115 GHz followed by a series of planar Schottky diode varactor multiplier stages to generate the required LO signal. The circuits have to be robust, relatively easy to assemble, and must provide broad fix-tuned bandwidth. A number of new technology initiatives being implemented to achieve these goals will be discussed. Approaches include quartz-based and substrate-less diode circuitry and integrated GaAs membrane technology. Recent results and progress-to-date will be presented.
Design and characterization of optical-THz phase-matched traveling-wave photomixers for difference-frequency generation of THz waves are presented. A dc-biased coplanar stripline fabricated on low-temperature-grown GaAs is illuminated by two non-collinear laser beams which generate moving interference fringes that are accompanied by THz waves. By tuning the offset angle between the two laser beams, the velocity of the interference fringe can be matched to the phase velocity of the THz wave in the coplanar stripline. The generated THz waves are radiated into free space by the antenna at the termination of the stripline. Enhancement of the output power was clearly observed when the phase-matching condition was satisfied. The output power spectrum has a 3-dB bandwidth of 2 THz and rolls off as approximately 9 dB/Oct which is determined by the frequency dependent attenuation in the stripline, while the bandwidth of conventional photomixer design has the limitation by the RC time constant due to the electrode capacitance. The device can handle the laser power of over 380 mW, which is 5 times higher than the maximum power handring capability of conventional small area devices. The results show that the traveling-wave photomixers have the potential to surpass small area designs, especially at higher frequencies over 1 THz, owing to their great thermal dissipation capability and capacitance-free wide bandwidth.
We developed a tunable, cavity-locked diode laser source at 850 nm for difference-frequency generation of coherent THz- waves. The difference frequency is synthesized by three fiber-coupled external-cavity diode lasers, where tow of the lasers are locked to adjacent modes of an ultra-stable Fabry-Perot cavity and the third laser is offset-phase- locked to the second cavity-locked laser using a tunable microwave oscillator. The first cavity-locked laser and the offset-locked laser produces the difference frequency, whose value is precisely determined by sum of integer multiple of free spectral range of the Fabry-Perot cavity and the offset frequency. The difference-frequency signal is amplified to 500 mW by the master oscillator power amplifier technique, simultaneous two-frequency injection-seeding with a single semiconductor optical amplifier. Here we demonstrate the difference-frequency generation of THz waves with the low- temperature-grown GaAs photomixers and its application to high-resolution spectroscopy of simple molecules. An absolute frequency calibration was carried out with an accuracy of approximately 10-7 using CO lines in the THz region.
We describe the preliminary design of the proposed Heterodyne Instrument for FIRST (HIFI). The instrument will have a continuous frequency coverage over the range from 480 to 1250 GHz in five bands, while a sixth band will provide coverage for 1410 - 1910 GHz and 2400 - 2700 GHz. The first five bands will use SIS mixers and varactor frequency multipliers while in the sixth band a laser photomixer local oscillator will pump HEB mixers. HIFI will have an instantaneous bandwidth of 4 GHz, analyzed in parallel by two types of spectrometers: a pair of wide-band spectrometers (WBS), and a pair of high- resolution spectrometer (HRS). The wide-band spectrometer will use acousto-optic technology with a frequency resolution of 1 MHz and a bandwidth of 4 GHz for each of the two polarizations. The HRS will provide two combinations of bandwidth and resolution: 1 GHz bandwidth at 200 kHz resolution, and at least 500 MHz at 100 kHz resolution. The HRS will be divided into 4 or 5 sub-bands, each of which can be placed anywhere within the full 4 GHz IF band. The instrument will be able to perform rapid and complete spectral line surveys with resolving powers from 103 up to 107 (300 - 0.03 km/s) and deep line observations.
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