The Heterodyne Spectrometer Instrument (HSI) is one of two instruments designed for the Far-IR Spectroscopy Space Telescope (FIRSST) recently proposed to NASA in response to the Astrophysics Probe Explorer call. HSI will be the first THz cryogenic heterodyne array receiver implemented for a space mission. It has extremely high spectral resolving power (R>10^6) in order to allow detailed spectral observations. HSI covers a very wide bandwidth range between 150 and 600 microns in only 3 bands, each equipped with two 5-pixel arrays. HSI enables highly sensitive dual-polarization, multi-pixel and multi-frequency observations on a space telescope, by a careful design and by employing low-heat dissipating, low-power, but high TRL components.
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.
High-density Polyethylene (HDPE), with a density above 0.95 g/cm3, has been widely used in terahertz systems. The advantages of low absorption loss, low refractive index and high rigidity make HDPE an ideal material for cryostat window, focus lens and substrate. HDPE can be machined easily and be used as a substrate material for components such as metal mesh filters and polarizers. What’s more, it is quite inert and can be used at cryogenic temperatures. On account of these applications, we need to characterize the dielectric property of HDPE precisely in a wide frequency range. In this paper, we present the transmittance measurements of a 2 mm thick HDPE sheet from 0.1 THz to 15 THz. Three kinds of measurement methods are employed to cover the whole frequency range. A vector network analyzer (VNA) combined with a quasi-optical transmissometer has been used to measure the transmittance and dielectric constant of HDPE from 0.16 THz to 0.18 THz at 300 K and 4 K. A Time Domain Spectrometer (TDS) is employed to cover the frequency range from 0.2 THz to 3 THz since the VNA can’t work upon 1 THz. A Fourier Transform Spectroscopy (FTS) has been used for the measurement from 3 THz to 15 THz since the TDS can’t achieve broad band and fast scan speed. The measured transmittance of HDPE is nearly 0.93 below 1 THz and decrease to 0.3 when the frequency increase to 15 THz. A rather elusive absorption band at 2.2 THz has also been observed. The dielectric constant of HDPE has been measured by VNA and TDS, showing a frequency independency from 0.1 THz to 3 THz.
The Origins Space Telescope (OST) is a NASA study for a large satellite mission to be submitted to the 2020 Decadal Review. The proposed satellite has a fleet of instruments including the HEterodyne Receivers for OST (HERO). HERO is designed around the quest to follow the trail of water from the ISM to disks around protostars and planets. HERO will perform high-spectral resolution measurements with 2x9 pixel focal plane arrays at any frequency between 468GHz to 2,700GHz (617 to 111 μm). HERO builds on the successful Herschel/HIFI heritage, as well as recent technological innovations, allowing it to surpass any prior heterodyne instrument in terms of sensitivity and spectral coverage.
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 (<30mA). Their power dissipation, when operated in CW mode, stays below 250mW over the whole operation range. These characteristics make the components compatible for compact integration.
Despite the small beam divergence of the 3rdorder DFB architecture employed, the emission pattern is not perfectly Gaussian. We have therefore developed a solution to re-shape the QCL’s output beam into a Gaussian one, using a dielectric hollow waveguide (DHW). We have realized a full study to perfect the coupling between the QCL and the DHW, as the coupling losses are the limiting factor. This solution stands out as the most efficient for our heterodyne system.
Finally, the low-power-dissipation QCL was combined with a hot-electron superconducting bolometer, to yield an ultra-compact heterodyne detector. Characterization of the heterodyne detector unit, obtained with a hot and a cold blackbody calibration set-up, will be presented during the talk.
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.
Superconducting Hot Electron Bolometer mixers offer the highest sensitivity for heterodyne detections at frequencies above 1 THz. Important efforts have been made these recent years to further increase the HEB mixers' sensitivity and working frequency and also to design multi-pixel configuration.
We present in this paper the developments of a non-standard quasi-optical membrane based HEB mixer where the commonly used focusing element, the silicon lens, is replaced by a micro-mirror and a membrane-based back-short. This configuration offers many advantages: easier processing for circuits at very high frequencies, better noise temperature brought by lower RF coupling loss and higher gain of the antenna. This design is also considered very attractive for multi-pixel receivers. The devices are made of phonon-cooled NbN HEB mixers processed on 1.4 μm thick stress-less Si3N4/Si02 membrane. Quasi-optical designs have been made for frequencies at 600 GHz and 2.5 THz. The design and the device fabrication process will be discussed and both DC and RF measurements at 600 GHz will be presented.
In this paper, the direct detection behaviors of a superconducting hot electron bolometer integrated with a log spiral
antenna are investigated by using Fourier Transform Spectrometer (FTS). We find the response of the bolometer to a
modulated signal can be detected by a lock-in amplifier not only from the DC bias current, but also from the output noise
power at the IF port of the HEB. We attribute the response in output noise power to Johnson noise and thermal
fluctuation noise. Both the current response and the output noise power response measured at different bias voltages can
be explained by one dimensional distributed hot spot model. In addition, the frequency response of the hot electron
bolometer measured from the response in DC bias current is in good agreement with that in IF output noise power.
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 Si3N4/SiO2 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 Si3N4/SiO2 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
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 Si3N4/SiO2 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.
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