We present a self-mixing terahertz-frequency gas spectroscopy technique using a multimode quantum cascade laser. A precision-micro-machined external waveguide module and a double-metal quantum cascade laser device are used to increase the optical feedback and the laser’s frequency tuning range. Methanol spectra are obtained using two laser modes at 3.362 THz and 3.428 THz simultaneously, with more than 8 absorption peaks resolved over a 17-GHz bandwidth, which provide minimum detectable absorption coefficients of 2.7×10-4 cm−1 and 4.9×10−4 cm−1, respectively. In contrast to all previous self-mixing spectroscopy, our multimode technique expands the sensing bandwidth significantly. This broadband spectroscopy technique can potentially be used for the identification and analysis of chemical, biological radiological and nuclear (CBRN) agents and explosives.
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.
We describe a Pb alloy superconducting (SIS) tunnel junction heterodyne receiver that has been constructed and tested over the frequency range 450 to 540 GHz and installed on the James Clerk Maxwell Telescope, Hawaii. The receiver uses a reduced height waveguide mount and a Pb alloy tunnel junction as the detecting element. Performance measurements made with the receiver installed on the telescope show a noise temperature (DSB) of 165 K at 460 GHz and 220 K at 490 GHz, measured in a 1 GHz instantaneous IF bandwidth centred at 4 GHz. The receiver demonstrates that Pb alloy junctions are sufficiently stable and reliable to allow use at a remote observing site at sub-millimetre wavelengths.
The Far Infrared Spectroscopic Explorer (FIRSPEX) is a novel European-led astronomy mission concept developed to enable large area ultra high spectroscopic resolution surveys in the THz regime. FIRSPEX opens up a relatively unexplored spectral and spatial parameter space that will produce an enormously significant scientific legacy by focusing on the properties of the multi-phase ISM, the assembly of molecular clouds in our Galaxy and the onset of star formation; topics which are fundamental to our understanding of galaxy evolution. The mission uses a heterodyne instrument and a ~1.2 m primary antenna to scan large areas of the sky in a number of discreet spectroscopic channels from L2. The FIRSPEX bands centered at [CI] 809 GHz, [NII]1460 GHz, [CII]1900 GHz and [OI]4700 GHz have been carefully selected to target key atomic and ionic fine structure transitions difficult or impossible to access from the ground but fundamental to the study of the multi-phase ISM in the Universe. The need for state-of-the-art sensitivity dictates the use of superconducting mixers configured either as tunnel junctions or hot electron bolometers. This technology requires cooling to low temperatures, approaching 4K, in order to operate. The receivers will operate in double sideband configuration providing a total of 7 pixels on the sky. FIRSPEX will operate from L2 in both survey and pointed mode enabling velocity resolved spectroscopy of large areas of sky as well as targeted observations.
TeraSCREEN is an EU FP7 Security project aimed at developing a combined active, with frequency channel centered at 360 GHz, and passive, with frequency channels centered at 94, 220 and 360 GHz, imaging system for border controls in airport and commercial ferry ports. The system will include automatic threat detection and classification and has been designed with a strong focus on the ethical, legal and practical aspects of operating in these environments and with the potential threats in mind. Furthermore, both the passive and active systems are based on array receivers with the active system consisting of a 16 element MIMO FMCW radar centered at 360 GHz with a bandwidth of 30 GHz utilizing a custom made direct digital synthesizer. The 16 element passive receiver system at 360 GHz uses commercial Gunn diode oscillators at 90 GHz followed by custom made 90 to 180 GHz frequency doublers supplying the local oscillator for 360 GHz sub-harmonic mixers. This paper describes the development of the passive antenna module, local oscillator chain, frequency mixers and detectors used in the passive receiver array of this system. The complete passive receiver chain is characterized in this paper.
Ultra-sensitive superconducting tunnel junction heterodyne receivers used for astronomy research require relatively low levels of local oscillator (LO) power. When configured as an imaging array, however, the LO power required substantially increases and the provision and distribution of a harmonically generated LO signal to multiple pixel elements becomes a technically challenging task. Furthermore, the difficulty of generating LO power is compounded as the operational frequency is increased into the supra-THz region (<1 THz). We will present our programme of research directed towards the provision of future THz astronomy receivers, in which we have been pursuing the development of enhanced harmonic up-conversion LO technology.
The successful European Space Agency (ESA) Planck mission has mapped the Cosmic Microwave Background (CMB) temperature anisotropy with unprecedented accuracy. However, Planck was not designed to detect the polarised components of the CMB with comparable precision. The BICEP2 collaboration has recently reported the first detection of the B-mode polarisation. ESA is funding the development of critical enabling technologies associated with B-mode polarisation detection, one of these being large diameter half-wave plates. We compare different polarisation modulators and discuss their respective trade-offs in terms of manufacturing, RF performance and thermo-mechanical properties. We then select the most appropriate solution for future satellite missions, optimized for the detection of B-modes.
We present the results of an instrument concept study for a low cost terahertz sounder of the mesosphere and lower
thermosphere (MLT). Recent advances in the development of Quantum Cascade Laser (QCL) technology to be used for
Local Oscillators (LOs) mean that it has now become viable for the first time to build compact, low weight heterodyne
receivers in the terahertz (THz) frequency range . Some of the most important atmospheric constituents of the MLT
region, e.g. atomic oxygen (O) and the hydroxyl radical (OH), can only realistically be measured at THz frequencies.
The technical challenges of THz remote sensing result in a large uncertainly of the global distribution of these species.
Recent research indicates that the MLT region exhibits links to processes associated with climate change. From this
follows a strong need to measure the composition and dynamic of the MLT region more accurately and more
We describe the design and characterisation of a cryogenic millimetre/sub-millimetre wave calibration load, cooled by
use of a closed cycle refrigerator that is used to test the performance of the ALMA receiver front-end system. Use of the
refrigerator removes the need for liquid cryogen (nitrogen) cooling and allows for long duration, and unattended
operation independent of orientation angle. Key requirements of the load include provision of a well-characterised and
constant brightness temperature over a wide frequency range (from ~100 GHz to ~1 THz) polarisation insensitivity, high
emissivity and mechanical stability. Test and verification of the load performance characteristics is achieved by using
several measurement techniques; these are presented and compared with measurements made using a liquid cryogen load
A compact, solid state, zenith looking 94 GHz meteorological radar is described. Samples of the reflectivity data obtained from representative samples of hydrometeors, including cirrus cloud and fog, are presented. This bistatic FMCW radar delivers continuous information on the distribution and thickness of cloud layers, permitting accurate determination of the cloud base altitude and upper limit. The maximum range is 16 km, with a corresponding resolution of 30 m: both range and averaging time are user selectable in ranges 2-16 km and 5-60 s respectively. A radiated millimetre wave power of below 200 mW yields a dynamic range of over 60 dB in the received signal.
TELIS (TErahertz and submm LImb Sounder) is a three-channel balloon-borne heterodyne spectrometer for
atmospheric research. The observational techniques of TELIS can be compared to the presently flying MLS instrument
on board NASA's EOS-Aura satellite, but TELIS is built with a new generation of cryogenic heterodyne detectors and
novel compact systems suitable for integration into the confined space of a balloon borne cryostat. TELIS will fly on the
MIPAS-B2 gondola. The two instruments together will yield the most complete set of stratospheric constituents,
measured so far. TELIS is a cooperation between the European institutes DLR (PI-institute), RAL and SRON. First
flight foreseen in the spring of 2008 from Teresina, Brasil.
The three TELIS receivers provide simultaneous vertical profile measurement of a range of molecules. The 500 GHz
channel is developed by RAL and will produce vertical profiles of BrO, ClO, O3 and N2O. The 1.8 THz channel is
developed by DLR and will mainly target the OH radical, and will also measure HO2, HCl, NO, NO2, O3, H2O, O2 and
HOCl. Finally the 480 - 650 GHz channel is developed by SRON and IREE and will measure profiles of ClO, BrO, O3,
HCl, HOCl, H2O and its 3 isotopomers, H2O2, NO, N2O, HNO3, CH3Cl and HCN.
In this paper, the science and technology of TELIS will be discussed with emphasis on the channel developed by
SRON. It contains a Superconducting Integrated Receiver (SIR), which combines on a 4x4 mm2 chip the low-noise SIS
mixer and its quasioptical antenna, a superconducting phase-locked Flux Flow Oscillator (FFO) acting as Local
Oscillator (LO) and a SIS harmonic mixer (HM) for FFO phase locking. The latest results from the pre-flight test and
integration campaigns will be presented.
TELIS (TErahertz and submm LImb Sounder) is a cooperation between European institutes, DLR, RAL, and SRON, to build a three-channel balloon-borne heterodyne spectrometer for atmospheric research. Many atmospheric trace gases have their rotational transitions in the sub millimeter and THz range, yielding a very rich spectrum. Limb sounding results in very accurate vertical profiles.
All three TELIS receivers will operate simultaneously. The 500 GHz channel is developed by RAL and will produce vertical profiles of BrO, ClO, O3, and N2O. The 1.8 THz channel is developed by DLR and will mainly target the OH radical, and will also measure HO2, HCl, NO, NO2, O3, H2O, O2, and HOCl. Finally the 550 - 650 GHz channel is developed by SRON and IREE and will measure profiles of ClO, BrO, O3 and its isotopologues, HCl, HOCl, H2O and its isotopologues, HO2, CO, NO, N2O, HNO3, CH3Cl, and HCN.
TELIS will fly on the MIPAS-B2 gondola. The two instruments together will yield the most complete set of stratospheric constituents. The qualification flight is foreseen in the winter of 2006/2007.
The TELIS instrument serves as a test bed for many novel cryogenic heterodyne technology: novel low-noise cryogenic heterodyne mixer detectors, novel low-noise cryogenic intermediate-frequency amplifiers, novel back-end spectrometer. In the presentation these technologies will be discussed and compared with 'conventional' technology as applied in the Microwave Limb Sounder (MLS) on EOS-Aura, launched in 2004. Emphasis will be on the science and technology of the channel developed by SRON. It contains a Superconducting Integrated Receiver (SIR), which combines on a 4x4 mm2 chip the low-noise Superconductor-isolator-Superconductor (SIS) mixer and its quasi-optical antenna, a superconducting phase-locked Flux Flow Oscillator (FFO) acting as Local Oscillator (LO) and SIS Harmonic Mixer (HM) for FFO phase locking. Latest test results and retrieval simulations will be presented.
A compact sub-millimetre wavelength Nb superconducting tunnel junction receiver (TIRGO) has been installed on the UKIRT facility, Hawaii. The receiver, used in combination with an acousto-optic spectrometer, exhibited excellent noise performance, achieving a best noise equivalent temperature of 280K (DSB) at 808GHz. Despite unfavourable observing conditions, spectral observations of a variety of astronomical sources were made that effectively verified the sensitivity and usefulness of the instrument for astronomical research. The design, construction and performance of the receiver system are described and some of the astronomical data acquired during the observation period briefly presented.
Photomixing is a flexible and efficient method of providing both local oscillator signals for heterodyne receivers and high frequency phase reference signals. Ultrafast, 70 GHz bandwidth, λ = 1.55 μm, photodiodes from u2t Photonics AG have been incorporated into three designs of mm-wave waveguide mounts. The photomixers utilise a thin freestanding gold foil, or a gold on dielectric, probe to couple power into the waveguide and to deliver the photodiode bias. The frequency coverage of the designs is from 70 GHz to 300 GHz. A method of rapidly characterizing the frequency response of these photomixers using spontaneous-spontaneous beating of light from an EDFA is described. Recent work has been directed at increasing the degree of integration of the photodiode with the waveguide probe and choke filter to reduce the frequency dependence of the output power. A simplified photomixer block manufacturing process has also been introduced. A combined probe and filter structure, impedance matched to both the coplanar output line on the photodiode chip and to 0.4 height milled waveguide, is presented. This matching is achieved over the W-band with a fixed waveguide backshort. We present modelled and experimental results showing the increased efficiency and smoother tuning. The design and frequency response of such a probe is reported. We also present the performance of a simpler mount, operating in the frequency range from 160 GHz to 300 GHz, which generates powers of around 10 μW up to 250 GHz.
Photomixing is a flexible and efficient method of providing both local oscillator signals for heterodyne receivers and high frequency phase reference signals. Ultrafast, 70 GHz bandwidth, = 1.55 m, photodiodes from u2t Photonics AG have been incorporated into mm-wave waveguide mounts. The photomixers utilise a thin gold probe to couple power into the waveguide and a gold-on-quartz choke filter to deliver photodiode bias. A method of rapidly characterizing the frequency response of these photomixers using spontaneous-spontaneous beating of light from an EDFA is described. Recent work has been directed at increasing the degree of integration of the photodiode, waveguide probe and choke filter to reduce the frequency dependence of the output power. A simplified photomixer block manufacturing process
has also been introduced. A combined probe and filter structure, impedance matched to both the coplanar output line on the photodiode chip and to 0.4 height milled waveguide, is presented. This matching is achieved over the W-band with a fixed waveguide backshort. We present modelled and experimental results showing the increased efficiency and smoother tuning. Subsequent integration steps could use the InP photodiode substrate to support the waveguide probe
and rf filter. The design and frequency response of such a probe is presented.
Methods for the photonic generation of stable millimetre-wave reference signals are examined and compared. In particular, the generation of optical comb lines with microwave frequency separation in an amplified fibre ring and by sideband generation with an optical phase modulator are reported. Two comb lines at a millimetre-wave difference frequency can be selected using optical filters and heterodyned. The fibre ring can produce comb lines over a broad range of up to about 1 THz, whereas the sideband generation scheme is limited to frequencies of about 160 GHz. Both methods produce stable, low-phase-noise millimetre-wave signals useful as phase/frequency references.
The transmission of such reference signals through optical fibre links of up to 9 km is also investigated. Differential dispersion effects can cause a power penalty in the received millimetre-wave signal, through the interaction of chromatic dispersion and SPM/XPM effects in the fibre, and through differential polarisation changes in the fibre causing non-alignment of the two optical fields at the photodiode. For the transmission of phase reference signals, the effects of differential dispersion, both chromatic and PMD, will cause phase variations in the received millimetre-wave signal, with the PMD effect being more serious due to its stochastic behaviour.
We present a design concept for a new state-of-the-art balloon borne atmospheric monitor that will allow enhanced limb sounding of the Earth's atmosphere within the submillimeter and far-infrared wavelength spectral range: TELIS, TErahertz and submm LImb Sounder. The instrument is being developed by a consortium of major European institutes that includes the Space Research Organization of the Netherlands (SRON), the Rutherford Appleton Laboratory (RAL) will utilize state-of-the-art superconducting heterodyne technology and is designed to be a compact, lightweight instrument cpaable of providing broad spectral coverage, high spectral resolution and long flight duration (~24 hours duration during a single flight campaign). The combination of high sensitivity and extensive flight duration will allow evaluation of the diurnal variation of key atmospheric constitutenets sucyh as OH, HO2, ClO, BrO togehter will onger lived constituents such as O3, HCL and N2O. Furthermore, TELIS will share a common balloon platform to that of the MIPAS-B Fourier Transform Spectrometer, developed by the Institute of Meteorology and Climate research of the over an extended spectral range. The combination of the TELIS and MIPAS instruments will provide atmospheric scientists with a very powerful observational tool. TELIS will serve as a testbed for new cryogenic heterodyne detection techniques, and as such it will act as a prelude to future spaceborne instruments planned by the European Space Agency (ESA).
MARSCHALS (Millimeter-wave Airborne Receivers for Spectroscopic CHaracterization in Atmospheric Limb Sounding) is being developed with funding from the European Space Agency as a simulator of MASTER (Millimeter-wave Acquisitions for Stratosphere Troposphere Exchange Research), a limb sounding instrument in a proposed future ESA Earth Explorer Core Mission. The principal and most innovative objective of MARSCHALS is to simulate MASTER's capability for sounding O3, H2O and CO at high vertical resolution in the upper troposphere (UT) using millimeter wave receivers at 300, 325, and 345 GHz. Spectra are recorded in these bands with 200 MHz resolution. As such, MARSCHALs is the first limb-sounder to be explicitly designed and built for the purpose of sounding the composition of the UT, in addition to the Lower Stratosphere (LS) where HNO3, N2O and additional trace gases will also be measured. A particular attribute of millimeter-wave measurements is their comparative insensitivity to ice clouds. However, to assess the impact on the measurements of cirrus in the UT, MARSCHALs has a near-IR digital video camera aligned in azimuth with the 235 mm limb-scanning antenna. In addition to UT and LS aircraft measurements, MARSCHALs is capable of making mid-stratospheric measurements from a balloon platform when fitted with a 400 mm antenna. Provision has been made to add further receiver channels and a high resolution spectrometer.
The Atacama Large Millimeter Array (ALMA), a joint project between Europe and the U.S. and at present in its design and development phase, is a major new ground based telescope facility for millimeter and submillimeter astronomy. Its huge collecting area (7000 m2), sensitive receivers and location at one of the driest sites on Earth will make it a unique instrument. We present preliminary design concepts for the overall receiver configuration. Optics and cryostat design concepts from OSO, OVRO, RAL, IRAM, NRAO and SRON and their main features are described.
The objective of the European project EMCOR was the development of a heterodyne receiver for the frequency range of 201 to 210 GHz for the measurement of the amounts of various minor constituents of the stratosphere involved in ozone chemistry. In order to be able to measure even very faint spectral lines a superconducting tunnel junction has been chosen as mixer element. Additionally, special care has been taken in developing the calibration unit of the system. Besides the classical hot-cold calibration three different balancing methods can be employed: a beam-switch technique with an atmospheric reference signal, a beam switch technique with a reference signal from a variable reference load or a frequency switch technique. The system has been integrated and is currently under testing. It will be installed at the International Scientific Station Jungfraujoch in he Swiss Alps and operated within the framework of the European Alpine stations of the Network for the Detection of Stratospheric Change.
Recent astronomical observations of neutral carbon at 492 GHz have shown that its distribution is widespread in interstellar molecular coulds. Studies of the distribution and excitation of neutral carbon are of key importance in understanding the chemistry of such regions. Observations of CI at 809 GHz to complement those at 492 GHz would be of great importance in such studies. We are currently building as SIS receiver for the frequency band 800-900 GHz for use in observing submillimeter spectral lines, including CI. The receiver will be operated on the TIRGO infrared telescope, situated on the summit of the Gornergrat, Switzerland (altitude 10,390 ft). It is anticipated that this receiver will be mounted on the TIRGO telescope towards the end of 1996, or the beginning of 1997.
A low Tc Pb alloy Superconductor-Insulator-Superconductor (SIS) tunnel junction heterodyne receiver has been constructed for astronomical use and tested over the frequency range of 400 to 540 GHz. Various alloy structures have been investigated in order to allow the production of small area SIS junctions with stable electrical characteristics and resistance to stress on cooling from 300 K to 4.2 K. Improvements in photolithography and thin film deposition techniques have been made that allow the fabrication of reliable sub-micron area junctions using suspended photoresist stencil and E-beam evaporation techniques. A single sub-micron area junction is mounted in a reduced height two tuner waveguide structure, which provides an optimum impedance match between the junction and the received signal. Performance measurements made with the receiver installed on the James Clerk Maxwell Telescope, Hawaii, show a total system double sideband noise equivalent temperature of 160 K at 460 GHz and 220 K at 490 GHz, measured in a 1 GHz instantaneous IF bandwidth centered at 4 GHz. The receiver demonstrates that Pb alloy tunnel junctions provide excellent sensitivity at submillimetre wavelengths and are sufficiently stable and reliable to allow use at a remote observing site.
A superconducting (SIS) tunnel junction heterodyne receiver has been constructed and tested over the frequency range450 to 540 GHz. The receiver uses a reduced height waveguide mount and a Pb alloy tunnel junction as the detectingelement. Performance measurements made with the receiver installed on the James Clerk Maxwell Telescope, Hawaii,show a noise temperature (DSB) of 165 K at 460 GHz and 220 K at 490 GHz, measured in a 1 GHz instantaneous IFbandwidth centred at 4 GHz. The receiver demonstrates that Pb alloy junctions are sufficiently stable and reliable toallow use at a remote observing site at sub-millimetre wavelengths.