Equipment for advanced optical coatings and materials research, characterisation and development for gravitational wave detectors and beyond

Lead Research Organisation: University of Glasgow
Department Name: School of Physics and Astronomy


Einstein's General Theory of Relativity (GR) predicts that dynamical systems in strong gravitational fields will release vast amounts of energy in the form of gravitational radiation. Gravitational waves are ripples in the fabric of spacetime and travel from their sources at the speed of light, carrying information about physical processes responsible for their emission, obtainable in no other way. The detection of gravitational waves (GWs) from the collision between two black holes (BHs) on 14th of June 2105 provided a spectacular validation of Einstein's theory. The signal had travelled 440 Mpc or around 1.5 billion light years before passing through the Earth and the detectors. It has opened a new window on the Universe, similar in that respect to when the first radio telescopes or the first X-ray telescopes were used. In the case of our GW detectors, they are sensitive to GWs in the frequency range of approximately 10 Hz to a few kHz.
Since that first detection, 5 more binary black hole collisions, or coalescences, have been observed and on August the 17th 2017, LIGO and Virgo detectors observed the signal from the coalescence of two solar mass compact bodies, either neutron stars or black holes. 1.7 seconds later a gamma-ray detector on a satellite called "Fermi" observed a gamma ray burst (GRB). GRBs have been seen for over 40 years and although their origin was not strictly known, it had been speculated that them must be from the result of the collision of two neutron stars. The combination of the GW signal and the GRB signal, along with further follow-up observations across the electromagnetic spectrum, showed that this event had been a neutron star- neutron star collision, leading to a short duration GRB and subsequent kilonova. The wealth of new physics and astrophysics that have been published as a result of all these detections has been extraordinary.
The worldwide network of interferometric detectors includes the German-UK GEO600, the French-Italian Virgo, the American Laser Interferometer Gravitational-Wave Observatory (LIGO) and is being enhanced with a new detector under construction - KAGRA in Japan. The LIGO and Virgo are improving their sensitivities and aim to meet their design goal within 2 years. Cooperation amongst different projects enables continuous data acquisition, with sensitivity to a wide range of sources and phenomena, over most of the sky.
This proposal for equipment will support the experimental programme of detector research and development supported by our Consolidated Grant 'Investigations in Gravitational Radiation' [ST/N005422/1]. Our aim is to improve the detectors and increase the number of signals we can detect. If we can increase sensitivity by a factor of ten, then we "see" signals from ten times further away, or a volume of space 1,00 times larger. This would increase detection rates also by a factor of 1,000. Detector sensitivity is mainly limited by thermal noise associated with the substrates of the mirrors, their reflective coatings, and their suspension elements, as well as by noise resulting from the quantum nature of the laser light used to sense the GW. This part of our research is targeted towards making innovative improvements in the areas of mirror coatings for low thermal noise, silicon substrates, cryogenic suspensions and improved interferometer topologies to combat quantum noise. The equipment requested will enable us to greatly increase the measurements we can make on materials that can potentially help us reduce the noise in our detectors.

Planned Impact

There are several groups who will benefit directly from this area of our research, that is the investigation in materials and optical coatings for GW detectors and different interferometry wavelengths and topologies. The position of the UK as a leading scientific nation will be enhanced by the output from this research and its subsequent impact on the field of GW detection. The proposed research will also ensure that the group continues to be seen as leading coating development within the LIGO collaboration and providing strong UK input to the field. The academics and other researchers within the group will benefit from this in the same way. Furthermore, the research output in terms of low loss and low absorption coatings would directly benefit the fields of optical frequency standards and optical clocks by allowing better short-term stability of the optical resonators used in those devices. Lower mechanical loss coatings could also benefit areas such as cavity quantum optics, allowing longer coherence times due to lower dissipation.
There are many examples of our track record on impact. On the experimental front, laser frequency stabilisation technology developed in Glasgow and JILA for GW detectors is used in every laboratory in the world where atomic spectroscopy is being carried out or atomic clocks are being built and operated. Silicate bonding technology developed for GEO600 in collaboration with Stanford University from the method employed in Gravity Probe B, has proved crucial to the European space agency for LISA Pathfinder, the demonstrator experiment for LISA, and has been transferred to industry in the UK through a KTP grant, with ongoing development with industry taking place under a European ITN grant. The same bonding technology, also now patented by us in Glasgow for application to silicon carbide, together with the research in ultra-low mechanical noise coatings may have application in the improvement of the noise levels of the stabilising cavities for sophisticated atomic clock systems. Vibration isolation is another area where significant developments have been made by us for the GW experiments and these techniques have influenced colleagues at Johns Hopkins Medical School in vibration reduction work for MRI imaging systems. Further, in the medical arena, interferometric and FEA techniques used within GW detectors are now being employed within cell biology for controlling the differentiation (fate) of stem cells, an area which is of potential benefit for growing autologous bone graft from a patient's own cells, in addition to the treatment of osteoporosis and bone fractures.
The design and modelling of optical mirror coatings is being translated into the design and fabrication of precise IR transmission filters for enhancing CO2 gas sensors, with a particular focus for use within medical capnography and anaesthetics.
Research results will be disseminated in weekly tele/video conferences within the collaboration; regular working group and collaboration meetings; conferences; publications and seminars both in the UK and globally. Finally, PhD students and PRDAs who were trained under STFC grants in this area have subsequently moved to other research institutions, including Caltech, MIT, Stanford University, NIKHEF (Holland), NIST (Gaithersburg) University of Maryland, the Albert Einstein Institute (Hannover and Golm), the University of Birmingham and the Australian National University.


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