Silica suspension and coating developments for advanced LIGO

Cagnoli, G. and Armandula, H. and Cantley, C.A. and Crooks, D.R.M. and Cumming, A. and Elliffe, E. and Fejer, M.M. and Gretarsson, A.M. and Harry, G.M. and Heptonstall, A. and Hough, J. and Jones, R. and MacKowski, J.-M. and Martin, I. and Murray, P. and Penn, S.D. and Perreur-Lloyd, M. and Reid, S. and Route, R. and Rowan, S. and Robertson, N.A. and Sneddon, P.H. and Strain, K.A. (2006) Silica suspension and coating developments for advanced LIGO. Journal of Physics: Conference Series, 32. pp. 386-392. ISSN 1742-6588 (

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The proposed upgrade to the LIGO detectors to form the Advanced LIGO detector system is intended to incorporate a low thermal noise monolithic fused silica final stage test mass suspension based on developments of the GEO 600 suspension design. This will include fused silica suspension elements jointed to fused silica test mass substrates, to which dielectric mirror coatings are applied. The silica fibres used for GEO 600 were pulled using a Hydrogen-Oxygen flame system. This successful system has some limitations, however, that needed to be overcome for the more demanding suspensions required for Advanced LIGO. To this end a fibre pulling machine based on a CO2 laser as the heating element is being developed in Glasgow with funding from EGO and PPARC. At the moment a significant limitation for proposed detectors like Advanced LIGO is expected to come from the thermal noise of the mirror coatings. An investigation on mechanical losses of silica/tantala coatings was carried out by several labs involved with Advanced LIGO R&D. Doping the tantala coating layer with titania was found to reduce the coating mechanical dissipation. A review of the results is given here.