Ultra-Low-Noise Photometric, Spectroscopic and Interferometric Imaging Technology for Astrophysics

The submillimetre-wave (3mm-300um) and far-infrared (300um-20um) regions of the electromagnetic spectrum are of considerable importance for astronomy because they contain a wealth of information about the cool, optically dark Universe. For example, the Cosmic Microwave Background radiation, which is a relic of the Big Bang, can be found at the longest wavelengths, whereas thermal radiation from distant, highly redshifted galaxies can be found at the shortest wavelengths. This part of the spectrum also contains thousands of spectral lines from numerous molecular and atomic species, which are important for studying the chemistry of regions where stars are being formed. It is exceptionally difficult, however, to make observations at submillimetre-wave and far-infrared and wavelengths because it is not possible to buy sufficiently sensitive cameras off of the shelf. Instead astronomers must develop their own imaging technology. These detectors must be highly sensitive, and must be cooled to temperatures of below 500mK. In addition, the instruments must be rugged, and capable of being flown in space. The proposed work aims to develop a new generation of extremely sensitive detectors and cameras by fabricating microcircuits out of materials called superconductors. Superconductors have the property that their electrical resistance falls to zero below some critical temperature, and magnetic flux is expelled. Indeed, the superconducting state is a special state of matter, and has many curious properties. By fabricating microcircuits out of the superconductors Nb, Ta, Al, and Mo, and by using modern Si micromachining techniques, it is possible to make detectors having exceptional properties. For example, our most recent infrared detectors are capable of detecting a light bulb being turned on and off for just 1 second at a distance of 10 million miles. The work will concentrate on understanding how to develop large-format cameras having thousands, and in some cases millions, of pixels. Four devices are of specific interest: (i) a device called a Transition Edge Sensor (TES), which operates by using the sharp transition of a superconductor to measure the minute change in temperature that occurs when infrared power is absorber by a tiny free-standing micro-machined silicon nitride island; (ii) a device called a Cold Electron Bolometer, which uses a solid-state refrigeration to achieve ultra-low-noise power detection; (iii) a device called a Kinetic Inductance Detector (KID), which essentially measures a small change that occurs in the amount by which a magnetic field penetrates into the surface of a superconductor when power is absorbed; and (iv) a device called a Superconductor Insulator Superconductor (SIS) mixer, which uses extremely thin layers of superconducting and insulating material to create diodes, which can be used to construct highly sensitive radio receivers. Each of these device types can be packed into arrays to form imaging systems of various kinds. Indeed, the wonderful scientific discoveries that were achieved in astronomy, in recent years, were only made possible by our ability to detect very weak signals coming from large radiotelescopes by using these tiny sub-micron devices. At the end of the program, we will have demonstrated a new generation of imaging technology based on superconducting devices, which will be available to construct the highly sensitive submillimetre-wave and far-infrared cameras that are needed for the next generation of ground-based and space-borne astronomy.

The primary objective of this proposal is the development of advanced imaging technology for the next generation of submillimetre-wave and far-infrared, national and international astronomical observatories. We emphasise the international flavour of our work because most modern observatories, both ground-based and space-borne, rely heavily on international support, either because the scale of the project is so large, or because the sophistication of the technology needed is beyond the capability of any one nation. We believe that this situation will persist for many years to come, and recognise that although there will be significant opportunities for home-nation instruments, it is essential for technical development to take place in an international context. Thus we see our role as taking an international lead in developing imaging technology that will enable major international projects and that will lever opportunity and influence for the UK astronomy community. In recent years, we contributed substantially to the success of many international astronomy projects (JCMT, ALMA, Herschel HIFI, etc.), and are now engaging in the high-profile projects of the future. The Letters of Support are evidence of this engagement: (i) The development of spectral-line array receiver technology, with eventual use on an ALMA Vertex Antenna, which is being placed in Greenland (Letter from Prof. Blundell). (ii) The development of supra-THz receiver technology to open up the operation of ALMA above 1THz (Letters from Prof. Russell, Prof. Wild, Prof. Belitsky). (iii) Development of FIR photometric imaging array technology for FIR wavelengths, such as FIRI (Letters from Prof. Hoevers, Prof. Mauskopf, Prof. Ade, Dr Jian-Rong Gao). (iv) Development of ultra-low-noise submillimetre-wave polarimetric imaging systems for the COrE mission, the Italian Space Agencies long-duration balloon experiment LPSE, and the QUIJOTE observatory in Tenerife (Letter from Prof. Piccirillo). Not only is our technology of pivotal importance for astronomy, it is highly intellectually worthy in its own right. The partner groups have made numerous contributions to theoretical and far-infrared optics, device physics, materials science and device processing. Many of these span the astronomy/nano-technology divide, exchanging knowledge in both directions. For example, we have recently created the first of model of heat transport in low-dimensional structures to include inelastic scattering. In the last 5 years the proposed team has published 144 journal and conference papers on advanced imaging technology. This energetic group will continue to provide a high level of academic output. Crucially our work will continue to have major industrial significance. As detailed in our Pathways to Impact Statement there is ample evidence of support for industry in areas relating to THz sensors for Earth observation, weather monitoring, communications, surveillance, biological sensing, medical and plasma diagnostics. For example, the RAL MMT group has worked closely with industrial concerns such as JCR Systems, SULA Ltd, SEA Ltd, Oxsensis, ComDev and Astrium UK, and national and international organisations such as UK HEIs, the UK Met Office, ESO, SAO, DLR. RAL's work has been so successful that they have recently spun out Teratech Components Ltd to exploit their Schotkky-diode foundry. Likewise, the Oxford Group has developed a new feed-horn technology, which is being commercialised by ISIS Innovation, and two companies, Atlantic Microwave and MM Microwaves. The Cambridge Group has a licensing agreement with Oxford Instruments PLC. All partners engage fully with many Outreach activities, giving talks to professional bodies, clubs, and schools. Ultimately we feel that past performance is the best indicator of future likely performance, and in this respect we have no doubt that the proposed Consortium can grow in strength and provide an even higher level of scientific and industrial impact.