Integrated Superconducting Spectrometer
Development of an Integrated Superconducting Submm Spectrometer for Radiostronomy and Atmosphere Monitoring
Tech Area / Field
- INS-MEA/Measuring Instruments/Instrumentation
- PHY-RAW/Radiofrequency Waves/Physics
- PHY-SSP/Solid State Physics/Physics
8 Project completed
Senior Project Manager
Mitina L M
Russian Academy of Sciences / Institute of Radioengineering and Electronics, Russia, Moscow
- Institute of Physics of Microstructures, Russia, N. Novgorod reg., N. Novgorod
- Deutsches Zentrum für Luft- und Raumfahrt e.V. / Institut fur Methodik der Fernerkundung, Germany, Oberpfaffenhofen\nChalmers University of Technology, Sweden, Göteborg\nHypres, USA, NY, Elmsford\nKansai Advanced Research Center, Japan, Nishi-ku\nSpace Research Organization Netherlands, The Netherlands, Groningen\nAgency for Industrial Science and Technology / AIST Tsukuba Central 2, Japan, Tsukuba\nDeutsches Zentrum für Luft- und Raumfahrt e.V., Germany, Köln\nTechnical University of Denmark, Denmark, Lyngby\nUniversity of Erlangen-Nurnberg, Germany, Erlangen
Project summaryThe main project objective is to develop and test an integrated superconducting quantum-limited high-resolution spectrometer for submm wave frequencies (up to 700 GHz). As a result of the project a family of Superconducting Integrated High Resolution Spectrometers with phase locked FFO will be developed and tested. This family includes a prototype of an airborne integrated spectrometer with a noise temperature close to the quantum limit hf/k, intended for monitoring ozone, chlorine compounds and industrial contaminants in the atmosphere. The desired parameters of this instrument are as follows: frequency range 500-650 GHz, noise temperature (DSB) below 250 K, spectral resolution better than 1 MHz. An important application of this receiver will be as an instrument for a Sub-mm Heterodyne balloon mission launched to study the Earth atmospheric chemistry and physics in the limb-sounding mode (TELIS). The TELIS project is a pre-cursor for the satellite space mission ACECHEM.
As a result of the project a method for detection of the complicated chemical compounds (including the components of the chemical weapons) will be developed; expected sensitivity of this method will allow to measure these substances on the level down to 10-7. Integrated spectrometer can be employed for distant detection of the complicated compounds; that is especially important for distant monitoring of Chemical Warfare Agents (CWA) destruction.
The concept of submm Superconducting Integrated Receiver (SIR) has been developed and experimentally proven in collaboration between IREE and SRON. The SIR is a single-chip device, which comprises an SIS-mixer with a quasioptical antenna and a superconducting local oscillator. Lightweight and compact ultra-sensitive submm SIRs with low power consumption are very attractive for both radio-astronomical research and remote monitoring of the Earth atmosphere. A few important achievements in the development of the quasi-optical integrated receiver with a FFO should be mentioned. i) A receiver DSB noise temperature below 100 K (i.e. close to the quantum limit) has been measured for an SIR with the internal FFO operated in the frequency range 480-520 GHz. ii) An intrinsic (free-running) FFO linewidth considerably below 1 MHz has been measured near 450 GHz. iii) Phase locking of a Josephson FFO to an external oscillator has recently been demonstrated experimentally, and a linewidth as low as 1 Hz was measured relative to a reference oscillator in the frequency range 270-440 GHz. iv) The antenna beam, approximately f/9 with sidelobes suppressed below - 16 dB, makes the integrated receiver suitable for coupling to a telescope. v) An imaging array of nine Integrated Receivers has been developed and tested.
Frequency resolution of a receiver (along with noise temperature and antenna beam pattern) is one of its major parameters for applications in spectral radio astronomy and atmosphere monitoring. The resolution determined by the instantaneous linewidth of the local oscillator and its long-time stability should be much less than 1 ppm of the center frequency. To measure the FFO linewidth a novel experimental technique has been developed by the project participants. A specially designed integrated circuit comprising FFO, SIS mixer, and microwave circuit elements needed for the rf coupling, is used for linewidth measurements in a wide frequency range up to 650 GHz. However, the observed FFO linewidth was almost one order of magnitude wider than predicted by the theory for a lumped Josephson tunnel junction.
In order to obtain the required frequency resolution the local oscillator must be phase-locked to an external reference. Up to now the phase locking of a Josephson oscillator has been demonstrated only for an FFO on resonant Fiske steps in the frequency range 270-440 GHz. In this case the free-running FFO line width is significantly decreased to a value of about 1 MHz by geometric Fiske resonances. At the same time the presence of these resonances makes continuous frequency tuning difficult. The increase of the intrinsic linewidth at voltages V > VJSC = 1/3ґ(D1 + D2) due to an abrupt increase of the internal damping (caused by Josephson self-coupling, JSC) considerably complicates phase locking of the FFO in this regime.
The problems described above constitute the main scientific challenges of the project, namely to develop a theory to adequately describe the FFO linewidth dependence on experimental parameters and to achieve a high spectral resolution of an integrated receiver by phase-locking of the superconducting FFO to an external reference oscillator at frequencies above 500 GHz. During the project a phase-locked superconducting local oscillator will be developed and integrated with a superconductor-insulator-superconductor (SIS) mixer and a planar superconducting antenna in a single-chip receiver. The main challenge of the project is to achieve both the high sensitivity of a SIS-mixer and the high spectral resolution of a receiver by phase-locking the superconducting Flux-Flow Oscillator (FFO) to an external reference oscillator.
Another important objective of the project is to study the fundamental limitations for the frequency and linewidth of cryogenic FFOs. For both atmospheric and astronomical missions an extension of the frequency range up to 1 THz is highly desirable. There are two main reasons why superconducting circuits incorporating Nb-AlOx-Nb tunnel junctions and Nb tuning circuits are limited to operating frequencies below 700 GHz The energy of a photon at frequencies above 700 GHz exceeds the superconducting energy gap of Nb causing huge losses in the Nb tuning circuits. Secondly, operation at 1 THz requires SIS junctions to be of submicrometer size with very high critical current density, up to 104 A/cm2. This is very difficult to obtain with reasonable yield for Nb-AlOx-Nb junctions. This may be achieved by using superconductors like NbTiN or NbN with higher critical temperature than Nb, both for tuning circuits and for tunnel junction electrode, and employing tunnel junctions with AlN barriers instead of AlOx. The ultimate goal of this part of the project is to fabricate and test all key elements necessary to use a SIR up to 1 THz.
New opportunities for microwave spectroscopy have appeared due to development of non-stationary methods, in which the measurements are faster than relaxation time of gas molecule polarization. Non-stationary spectroscopy is based on the effect of coherent spontaneous radiation of gas molecules. The molecules absorb resonantly a pulse of electromagnetic radiation and macroscopic dipole momentum is formed in the gas. Absorbed energy coherently re-radiates with a frequency of molecular transition. In spectrometers, using this approach, the high resolution and sensitivity can be realized simultaneously, that especially important for both analytical study of the complicated molecules (e.g. components of the chemical weapons) and analysis of the multi-component gas mixtures. Method of microwave spectroscopy allows to identify unambiguously the molecules under test by measurement of one of the spectral lines. Furthermore, the microwave spectral lines are not overlapping that gives an opportunity to measure various combinations of the components in the gas mixture. The microwave spectrometers of a new generation were developed and studied by the IPM within 15 years.
The high intensity absorption lines of molecules under test do not overlap that allows to measure the most of all possible combinations of components in gas mixtures. The device does not require any readjustment for the analysis of various components of a gas mixture. The ground and air based spectrometers allow to reach a high accuracy and speed of measurement of radiation’s parameters (minimal time of measurement is limited by 1-2 ms). The practical realization of the spectrometer using the phenomena of coherent spontaneous radiation can be provided by means of frequency or phase manipulation of radiation. The spectrometer with phase manipulation provides the best sensitivity among all known methods of microwave spectroscopy. For example, the Lewisite spectrum in the frequency range 53-78 GHz and 256-535 GHz has been investigated using the developed at IPM spectrometer. The preliminary results have clearly shown the unique sensitivity of proposed approach, which allowed measuring the Lewisite concentration in air at a level 10-7. A possibility to detect the very important for ecology gases like SO2, CO, NO, H2S, NH3 on the bottom of sensitivity has been demonstrated. An employment of the superconducting receivers with ultimate sensitivity give an opportunity to realize the potentialities of the microwave spectroscopy.
It is worth to notice that successful completing of this program will allow the Integrated Spectrometer to be used both in the laboratory and for distant monitoring of the atmosphere to detect different contaminations and Chemical Warfare Agents (CWA). This method is preferable for such purposes compare to Infrared and Optical spectroscopy because of smaller absorption of a microwave radiation in the atmosphere; it provides the best sensitivity and spectral resolution. Obviously that is especially important for distant monitoring of CWA destruction. The proposal is based on extensive preliminary investigations carried out by the project groups over the last few years in the field of superconducting electronics. Technological facilities and reliable procedures for fabrication of Nb-AlOx-Nb tunnel junctions have already been developed at IREE. First in the world, a laboratory Integrated Receiver was developed and successfully tested at 500 GHz (IREE, SRON). Presently practical realization of the Integrated Receiver concept is being demonstrated, and a DSB noise temperature below 100 K, just 4 times above the quantum limit, has been obtained at 500 GHz.
In summary, all results listed above give a fine background for future important studies and developments. The high scientific and technological level of the project partners warrants the proposed end results: a series of front-line superconducting integrated receiving devices, in particular an integrated superconducting quantum-limited submm wave spectrometer for TELIS. The design parameters of this instrument are: i) frequency range 500-650 GHz, ii) noise temperature (DSB) below 250 K, iii) spectral resolution better than 1 MHz.
The new ambitious radio-astronomy multi-dish projects (e.g. ALMA) would gain considerably by using single-chip SIRs with phase-locked FFO due to their lower price and better serviceability than conventional approaches. The Integrated Spectrometer is particularly promising as a laboratory instrument for detection of radiation from the newly developed semiconducting and superconducting submm wave sources. When mass-produced the estimated cost of a microcircuit for an Integrated Spectrometer would be of order 1,000 USD, much lower than the 20-25,000 USD presently paid for a conventional oscillator in this frequency range, usually based on a BWO with powerful magnet and high-voltage power supply or a Gunn oscillator with a harmonic multiplier. Mass production of such spectrometers gives a chance for their application for analysis of the breathed out air at medical survey. Most important for medical analysis spectral lines can be detected in adsorption of submillimeter waves.
It is important to emphasize that most of the project study will be done in the collaboration with a leading western scientific institutions, which will be interested not only in project results, but will provide their own unique technological and measuring facilities for project execution (see appended Letters of Support). Furthermore, some of the foreign collaborators are ready to supply Russian partners (using the ISTC infrastructure) by a set of modern equipment in case of funding of the project by ISTC.
The project undoubtedly fits the aims and tasks of ISTC. It allows a large group of Russian scientists and engineers from IREE and IPM, having great knowledge and qualification in development of military applications, to be reoriented completely onto the peaceful applications. Thereby any possibilities of contacts with the developing countries on transferring special knowledge and research results for military applications will be completely cancelled.
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