Investigation of mechanical dissipation in CO_2 laser-drawn fused silica fibres and welds
The planned upgrades to the LIGO gravitational wave detectors include monolithic mirror suspensions to reduce thermal noise. The mirrors will be suspended using CO2 laser-drawn fused silica fibres. We present here measurements of mechanical dissipation in synthetic fused silica fibres drawn using a CO_2 laser. The level of dissipation in the surface layer is investigated and is found to be at a similar level to fibres produced using a gas flame. Also presented is a method for examining dissipation at welded interfaces, showing clear evidence of the existence of this loss mechanism which forms an additional component of the total detector thermal noise. Modelling of a typical detector suspension configuration shows that the thermal noise contribution from this loss source will be negligible.
© 2010 IOP Publishing Ltd. Print publication: Issue 3 (7 February 2010); received 2 October 2009; in final form 2 December 2009; published 15 January 2010. We would like to thank our colleagues in the GEO600 project, the Scottish Universities Physics Alliance (SUPA) and the LIGO Scientific Collaboration for their interest in this work. We also wish to thank the ILIAS Strega project and Leverhulme Trust for support. We are grateful for the financial support provided by the STFC and the University of Glasgow in the UK and the NSF in the USA. The LIGO Observatories were constructed by the California Institute of Technology and Massachusetts Institute of Technology with funding from the NSF under cooperative agreement PHY-9210038. The LIGO Laboratory operates under cooperative agreement PHY-0107417.