Design and development of the advanced LIGO monolithic fused silica suspension

Cumming, A. V. and Bell, A. S. and Barsotti, L. and Barton, M. A. and Cagnoli, G. and Cook, D. and Cunningham, L. and Evans, M. and Hammond, G. D. and Harry, G. M. and Tokmakov, Kirill (2012) Design and development of the advanced LIGO monolithic fused silica suspension. Classical and Quantum Gravity, 29 (3). 035003. ISSN 0264-9381 (https://doi.org/10.1088/0264-9381/29/3/035003)

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Abstract

The detection of gravitational waves remains one of the most challenging prospects faced by experimental physicists. One of the most significant limits to the sensitivity of current, and future, long-baseline interferometric gravitational wave detectors is thermal displacement noise of the test masses and their suspensions. Suspension thermal noise will be an important noise source at operating frequencies between approximately 10 and 30 Hz, and it results from a combination of thermoelastic damping, surface loss and bulk loss associated with the suspension fibres, and weld loss from their attachment. Its effects can be reduced by minimizing thermoelastic loss and optimizing pendulum dilution factor via the appropriate choice of geometry of the suspension fibre and attachment geometry. This paper will discuss the design and fabrication of a prototype of the fused silica suspension stage for use in the advanced LIGO (aLIGO) detector network, analysing in detail the design of the fused silica attachment pieces (ears), together with the suspension assembly techniques. We also present a full thermal noise analysis of the prototype suspension, taking into account for the first time the precise shape of the actual fibres used, and weld loss. We shall demonstrate the suitability of this suspension for installation into aLIGO.