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

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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.