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4GREAT is an extension of the German Receiver for Astronomy at Terahertz frequencies (GREAT) operated aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). The spectrometer comprises four different detector bands and their associated subsystems for simultaneous and fully independent science operation. All detector beams are co-aligned on the sky. The frequency bands of 4GREAT cover 491-635, 890-1090, 1240-1525 and 2490-2590 GHz, respectively. This paper presents the design and characterization of the instrument, and its in-flight performance. 4GREAT saw first light in June 2018, and has been offered to the interested SOFIA communities starting with observing cycle 6., Accepted for publication in IEEE Transactions on Terahertz Science and Technology

The Heterodyne Receiver for Origins (HERO) is the first detailed study of a heterodyne focal plane array receiver for space applications. HERO gives the Origins Space Telescope the capability to observe at very high spectral resolution (R = 107) over an unprecedentedly large far-infrared (FIR) wavelengths range (111 to 617 μm) with high sensitivity, with simultaneous dual polarization and dual-frequency band operation. The design is based on prior successful heterodyne receivers, such as Heterodyne Instrument for the Far-Infrared /Herschel, but surpasses it by one to two orders of magnitude by exploiting the latest technological developments. Innovative components are used to keep the required satellite resources low and thus allowing for the first time a convincing design of a large format heterodyne array receiver for space. HERO on Origins is a unique tool to explore the FIR universe and extends the enormous potential of submillimeter astronomical spectroscopy into new areas of astronomical research.

We report on the demonstration of an ultra-high-sensitivity superconducting hot-electron-bolometer (HEB) heterodyne receiver at 2.5 THz with a low-power-consumption quantum cascade laser (QCL) as its local oscillator (LO). The 2.5-THz QCL, with an electrical power dissipation of about 0.9 W in continuous wave mode, is integrated with a spiral-antenna-coupled niobium nitride HEB mixer in a single block. The mixer performance is barely affected by heat dissipation from the QCL when the receiver is cryogenically cooled either by a wet LHe Dewar or by a closed-cycle 4-K pulse-tube cooler. Measured with a vacuum setup, the heterodyne receiver exhibits a double sideband receiver noise temperature of 800 K at 2.5 THz with the IR filter contribution corrected, which is approximately 7hυ/kB. And the Allan variance time at 80-MHz noise bandwidth is found to be about 10 s when a proportional-integral-derivative controller is adopted to control the LO power.

Quasi-optical superconducting hot-electron bolometer (HEB) mixers have shown a competitive sensitivity at a frequency slightly lower than 1 THz when compared to superconducting SIS mixers. The advantage of low LO power requirement makes superconducting HEB mixers, especially suitable for array application. The far-field beam pattern, as well as coupling efficiency of quasi-optical superconducting HEB mixers, depends strongly upon the lens shape and the dielectric constant of the lens material. Therefore, in this letter we precisely measured the dielectric constant and loss tangent of high resistivity silicon at 4, 77, and 300 K in the frequency range of 700–900 GHz where many important molecular lines located. The measurements are performed by employing a quasi-optical vector network analyzer with a dynamic range as high as 110 dB to ensure high precision measurement. In addition, the dielectric constant of high-density polyethylene (HDPE) and polymethylpentene (TPX/PMP) are also measured since they are widely used in terahertz quasi-optical system.

In this paper, we investigate the critical temperature dependence of the performance of niobium nitride superconducting hot electron bolometer (HEB) mixers. The input noise temperature and intermediate frequency (IF) noise bandwidth of superconducting HEB mixers of different critical temperatures $T_{c}$ (between 6 and 12 K) are simulated with a hot spot model. Simulation results show that the mixer input noise temperature is the lowest at $T_{c}$ approximately equal to 7–9.5 K and the IF noise bandwidth increases with $T_{c}$ . We also measure three superconducting HEB mixers of different critical temperatures (i.e., 7.5, 8.8, and 10.3 K) at 0.85 and 1.3 THz. An agreement between measurement and prediction is observed.

A 2 x 2 local oscillator beam divider for pumping a hot electron bolometer mixer array is designed at 1370 GHz. Traditional rectangular waveguide based H-plane and E-plane junctions are used to construct the feeding network. Two 400-μm thick silicon wafers are used to build the feeding network, and an aluminum plate is used to build the circular horn array. Multilayer micromachining and multilayer stack assembling are the two key technologies employed in building this beam divider.

The D/H ratio in cometary water has been shown to vary between 1 and 3 times the Earth's oceans value, in both Oort cloud comets and Jupiter-family comets originating from the Kuiper belt. We present new sensitive spectroscopic observations of water isotopologues in the Jupiter-family comet 46P/Wirtanen carried out using the GREAT spectrometer aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). The derived D/H ratio of $(1.61 \pm 0.65) \times 10^{-4}$ is the same as in the Earth's oceans. Although the statistics are limited, we show that interesting trends are already becoming apparent in the existing data. A clear anti-correlation is seen between the D/H ratio and the active fraction, defined as the ratio of the active surface area to the total nucleus surface. Comets with an active fraction above 0.5 typically have D/H ratios in water consistent with the terrestrial value. These hyperactive comets, such as 46P/Wirtanen, require an additional source of water vapor in their coma, explained by the presence of subliming icy grains expelled from the nucleus. The observed correlation may suggest that hyperactive comets belong to a population of ice-rich objects that formed just outside the snow line, or in the outermost regions of the solar nebula, from water thermally reprocessed in the inner disk that was transported outward during the early disk evolution. The observed anti-correlation between the active fraction and the nucleus size seems to argue against the first interpretation, as planetesimals near the snow line are expected to undergo rapid growth. Alternatively, isotopic properties of water outgassed from the nucleus and icy grains may be different due to fractionation effects at sublimation. In this case, all comets may share the same Earth-like D/H ratio in water, with profound implications for the early solar system and the origin of Earth's oceans., Comment: 9 pages, 5 figures

We study experimentally the resistive behaviors of a niobium nitride superconducting hot-electron bolometer (HEB) device driven by magnetic field and terahertz radiation. We find that the resistance of the superconducting HEB device emerges due to time-dependent changes of the macroscopic quantum phase by flux-flow events. The flux-flow resistance is found to be increased linearly with magnetic field at low vortex velocities and is enhanced by terahertz radiation. At high vortex velocities, there is an obvious non-linear change, which can be well interpreted by viscous flux-flow instability predicted by the Larkin and Ovchinnikov theory. In addition, we demonstrate a technique taking use of the device resistance dependence on magnetic field to stabilize the superconducting HEB device.

We report on the investigation of optimal bias region of a wide-band superconducting hot electron bolometer (HEB) mixer in terms of noise temperature performance for multi-pixel heterodyne receiver application in the 5-meter Dome A Terahertz Explorer (DATE5) telescope. By evaluating the double sideband (DSB) receiver noise temperature (T rec) across a wide frequency range from 0.2 THz to 1.34 THz and with a large number of bias points, a broad optimal bias region has been observed, illustrating a good bias applicability for multipixel application since the performance of the HEB mixer is uniquely determined by each bias point. The noise temperature of the HEB mixer has been analyzed by calibrating the noise contribution of all RF components, whose transmissions have been measured by a time-domain spectroscopy. The corrected noise temperature distribution shows a frequency independence relation. The dependence of the optimal bias region on the bath temperature of the HEB mixer has also been investigated, the bath temperature has limited effect on the lowest receiver noise temperature until 7 K, however the optimal bias region deteriorates obviously with increasing bath temperature.

International audience

Our understanding of the physics/chemistry of the interstellar medium increased since we got the capacity to develop heterodyne spectroscopy tools in the THz frequency range. For instance, an example of an important emission line in astronomy is the fine structure of the molecular deuterated hydrogen at 2.675 THz. Heterodyne detection requires local oscillator sources that operate a few GHz away from the frequency of interest. THz quantum cascade lasers (QCL) emerge therefore as suitable sources. The combination of quantum cascade laser as local oscillator and ultra-sensitive hot electron bolometers for the mixing is so far the sole solution available in order to realise a compact and ultra-sensitive heterodyne detection system. The first building block of our heterodyne detector is a spectrally single mode, low power consumption THz QCL operating at a specified target frequency. We developed devices with low threshold driving currents (

In this paper, the performance of a twin-slot antenna coupled NbN superconducting HEB mixer based on a new device fabrication process is thoroughly investigated. The measured lowest double-sideband receiver noise temperature is about 600 K at 1.3 THz, and reduced to 300 K after eliminating all the quasi-optical losses. The spectral response of the HEB mixer is characterized by a Fourier Transform Spectrometer (FTS) and its calibrated spectrum is in good agreement with the simulated one. In addition, the far-field beam pattern of this HEB mixer is characterized by a near-field measurement technique. The measured results agree well with the simulations too.

International audience

International audience; This article presents current R&D activities at Observatoire de Paris - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique in the fields of low noise mixers and local oscillators for heterodyne instruments dedicated to astrophysics, planetology and the sciences of the atmosphere.

The performance of a 1.3 THz twin-slot antenna coupled superconducting hot-electron-bolometer (HEB) mixer integrated with elliptical lenses of different extension lengths are investigated. The elliptical lenses have the same radius but different extension lengths: 1.109 mm, 1.149 mm, 1.189 mm and 1.229 mm. The measured noise temperature and frequency response appears insensitive to the lens extension length. The far-field beam-patterns, directivity and Gaussicity are clearly related to the lens extension length.

In this paper, we report on the measured and simulated far-field beam-patterns of a quasi-optical NbN superconducting hot electron bolometer (HEB) mixer at 600GHz. This superconducting HEB mixer consists of an extended hemispherical lens with a diameter of 12.7mm and an extension length of 2.45mm, a twin-slot planar antenna (two slots measuring 148.5μm × 10.4μm with a separation of 78.98μm) and a 5.5-nm thick NbN thin-film micro-bridge with an area of 2μm × 0.2μm . The far-field beam pattern of this mixer is measured by a direct-detection technique with a dynamic range of nearly 25dB, showing an FWHM beam angle of 2.7° and -18dB level of the first side-lobe. The measured beam of the quasi-optical mixer is nearly collimated and has good Gaussian beam efficiency. In addition, the far-field beam-pattern is measured at different DC bias voltages of the superconducting HEB mixer and at different bath temperatures. The measured results are compared with the ones simulated by two different methods. Detailed measurement and simulation results will be presented.

We interpret the experimental observation of a frequency-dependence of superconducting hot electron bolometer (HEB) mixers by taking into account the non-uniform absorption of the terahertz radiation on the superconducting HEB microbridge. The radiation absorption is assumed to be proportional to the local surface resistance of the HEB microbridge, which is computed using the Mattis-Bardeen theory. With this assumption the dc and mixing characteristics of a superconducting niobium-nitride (NbN) HEB device have been modeled at frequencies below and above the equilibrium gap frequency of the NbN film.

International audience; We present the first results of the unbiased survey of the L1157-B1 bow shock, obtained with HIFI in the framework of the key program Chemical HErschel Survey of Star forming regions (CHESS). The L1157 outflow is driven by a low-mass Class 0 protostar and is considered the prototype of the so-called chemically active outflows. The bright blue-shifted bow shock B1 is the ideal laboratory for studying the link between the hot (~1000-2000 K) component traced by H2 IR-emission and the cold (~10-20 K) swept-up material. The main aim is to trace the warm gas chemically enriched by the passage of a shock and to infer the excitation conditions in L1157-B1. A total of 27 lines are identified in the 555-636 GHz region, down to an average 3σ level of 30 mK. The emission is dominated by CO(5-4) and H2O(110-101) transitions, as discussed by Lefloch et al. in this volume. Here we report on the identification of lines from NH3, H2CO, CH3OH, CS, HCN, and HCO+. The comparison between the profiles produced by molecules released from dust mantles (NH3, H2CO, CH3OH) and that of H2O is consistent with a scenario in which water is also formed in the gas-phase in high-temperature regions where sputtering or grain-grain collisions are not efficient. The high excitation range of the observed tracers allows us to infer, for the first time for these species, the existence of a warm (≥200 K) gas component coexisting in the B1 bow structure with the cold and hot gas detected from ground. Herschel is an ESA space observatory with science instruments provided by European-led principal Investigator consortia and with important participation from NASA.Table 1 is only available in electronic form at http://www.aanda.org

International audience; Various buffer layers have been investigated in order to improve the crystalline quality of NbN ultra-thin films. The structural properties, the thickness, the surface morphology of 5-10 nm NbN films have been studied by different techniques. Uncertainty on thickness measurements in this range and the relation between NbN film quality and gain bandwidth are discussed in the framework of their use in Hot Electron Bolometers (HEB).

A 16 pixel heterodyne receiver for 2.5 THz has been developed based on NbN superconducting hot-electron bolometer (HEB) mixers. The receiver uses a quasioptical RF coupling approach where HEB mixers are integrated into double dipole antennas on 1.5μm thick Si 3 N 4 /SiO 2 membranes. Spherical mirrors (one per pixel) and backshort distance from the antenna have been used to design the output mixer beam profile. The camera design allows all 16 pixel IF readout in parallel. The gain bandwidth of the HEB mixers on Si 3 N 4 /SiO 2 membranes was found to be 0.7÷0.9 GHz, which is much smaller than for similar devices on silicon. Application of buffer layers and use of alternative types of membranes (e.g. silicon-on-insulator) is under investigation.

We present in this paper the front-end design and the results of RF simulations, carried out with Microwave Studio (CST) and HFSS for SHAHIRA (Submillimeter Heterodyne Array for High-speed Radio Astronomy), a 4x4 heterodyne array at 2.5 THz and 4.7 THz. One can then observe 16 spatial positions at 2 frequencies. The design has been chosen to be quasi-optic, because of its simplicity, novelty and multi-pixels applicability. Pixels are made of Niobium Nitride HEB mixers with double-slot antennas, processed on 1 μm thick stress-less Si3N4/SiO2 membrane. The use of the membrane shows numerous advantages: for instance the use of the mixers at higher RF frequencies, a better power coupling efficiency or a solution for avoiding dielectric modes, losses and reflections. This work is supported by ESA and is a collaboration between LERMA, CHALMERS and LAAS. The Camera is expected to find applications, for SOFIA or CIDRE.

Observation and analysis of submillimeter-wave radiation (300GHz-3THz) in astronomy and atmospheric sciences requires increasingly performant receivers. The most sensitive receivers working in this range of electromagnetic spectrum use superconductor-insolator-superconductor (SIS) junctions. In order to increase the bandwidth and the sensitivity, we are developing a quantum-noise limited heterodyne receiver based on several parallel SIS junctions with broad (larger than 30%) fixed tuned bandwidth. These circuits can be viewed as passband filters which have been optimized by varying the spacings between junctions. We have designed such 5-junction arrays for operation in the range 480-640 GHz. Fabrication and heterodyne characterization of these devices has been done. The 1 μm2 junctions current density ranges from 4 to 13 kA/cm2, using optical lithography and Nb/Al2Nb5/Nb trilayer sputtering technology. The fabrication process and yield are presented in this paper, along with measured performances© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report in this paper a new concept for 2.7 THz superconducting Niobium nitride (NbN) Hot-Electron Bolometer mixer (HEB). The membrane process was developped for space telecommnunication applications a few years ago and the HEB mixer concept is now considered as the best choice for low-noise submillimeter-wave frequency heterodyne receivers. The idea is then to join these two technologies. The novel fabrication scheme is to fabricate a NbN HEB mixer on a 1 μm thick stress-less Si 3 N 4 /SiO 2 membrane. This seems to present numerous improvements concerning : use at higher RF frequencies, power coupling efficiency, HEB mixer sensitivity, noise temperature, and space applications. This work is to be continued within the framework of an ESA TRP project, a 2.7 THz heterodyne camera with numerous applications including a SOFIA airborne receiver. This paper presents the whole fabrication process, the validation tests and preliminary results. Membrane-based HEB mixer theory is currently being investigated and further tests such as heterodyne and Fourier transform spectrometry measurement are planed shortly.

We report on the status of the development of a 30% bandwidth tunerless SIS double-sideband mixer for the “Band 1” (480 GHz-630 GHz) channel of the heterodyne instrument (HIFI) of ESA’s Herschel Space Observatory, scheduled for launch in 2007. After exposing the main features of our mixer design, we present the performance achieved by the demonstration mixer, measured via Fourier Transform Spectroscopy and heterodyne Y factor calibrations. We infer from a preliminary mixer analysis that the mixer has very low, quantum-limited noise and low conversion loss. We also report on some pre-qualification tests, as we currently start to manufacture the qualification models and design the last iteration of masks for SIS junction production.

International audience; An iterative alternate projection-based algorithm is developed to design structured surfaces able to generate any far-field beam pattern at GHz and THz frequencies. To validate the algorithm, two structured profiles (a reflective one and a transmissive one) are designed to generate four beams of similar intensity at 610 GHz. The two prototypes are fabricated and tested to experimentally evaluate their performance. Experimental measurements confirm a good agreement with computer simulations using Feko TM and, therefore, validate the method.

International audience; For heterodyne array receivers, phase gratings are useful to divide the local oscillator (LO) signal into several beams to pump the mixers of an array. We have developed a computer model to compute general phase profiles that can be non periodic. The model allows to set many input parameters and constraints so that the output can be optimized for any specific case. The phase profiles can be used to design phase gratings that can be used in transmission or in reflection.

We demonstrate an ultra-compact Terahertz (THz) heterodyne detec- tion system based on a quantum cas- cade laser (QCL) as local oscillator and a hot electron bolometer (HEB) for the mixing. It relies on a new opti- cal coupling scheme where the local oscillator signal is coupled through the air side of the planar HEB an- tenna, while the signal to be de- tected is coupled to the HEB through the lens. This technique allows us to suppress the beam splitter usu- ally employed for heterodyne mea- surements. The mixer is a Niobium Nitride HEB with a log-spiral planar antenna on silicon and mounted on the back of a plano-convex silicon lens. We have developed a low power consumption and low beam di- vergence 3rd-order distributed feed- back laser with single mode emis- sion at the target frequency of 2.7 THz to be used as local oscillator for the heterodyne receiver. The cou- pling between the QC laser and the the HEB has been further optimized, using a dielectric hollow waveguide that reliably increases the laser beam directivity up to 55 dBi. Upon the high beam quality, sufficient output power in a single mode at the tar- geted frequency and low power dissi- pation of our local oscillator, we have build an ultra compact THz hetero- dyne receiver with sensitivity close to the state of the art at 2.7 THz., Nous avons développé un récepteur hétérodyne terahertz (THz) compact et ultra-sensible à base de laser à cascade quantique (QCL) comme oscillateur local et de bolomètre à électron chaud (HEB) comme mélangeur. Le récepteur est basé sur un nouveau concept pour le couplage quasi-optique entre l'oscillateur local et le mélangeur ce qui a permis de ne pas utiliser de lame semi-réfléchissante pour la superposition du signal provenant du QCL et du signal à détecter. Le mélangeur utilisé est un HEB en nitrure de niobium avec une antenne planaire formée d’une double hélice log-spiral. Le HEB est monté sur la partie plane d’une lentille convexe en silicium. L’oscillateur local est un QCL que nous avons développé avec un système de contre-réaction répartie du troisième ordre avec une faible dissipation thermique, un faisceau peu divergent et un fonctionnement mono-mode à la fréquence cible de 2.7 THz. Le couplage entre l’oscillateur local et le mélangeur HEB a également été amélioré en couplant le QCL avec une fibre creuse en diélectrique ce qui a permis d’améliorer la directivité du faisceau laser à 55 dBi. Grâce aux précédents résultats, nous avons obtenu un récepteur THz hétérodyne compact qui présente une sensibilité proche de l’état de l’art à 2.7 THz.