Improved fused silica fibres for the advanced LIGO monolithic suspensions

To further increase the sensitivity of the advanced LIGO (aLIGO) gravitational wave detectors, two major upgrades of the monolithic fused silica suspension are considered: a higher stress in the suspension fibres and a longer final suspension stage. One of the challenges for this upgrade will be producing thinner and longer fibres that can hold the test mass safely. We demonstrate that laser power fluctuations during the fibre fabrication process can produce diameter variations and potentially weak fibres. We present a laser intensity stabilisation technology for fused silica fibre fabrication using a camera system to monitor heating. Fibres fabricated with this new technique showed a 34% decrease in the interquartile range of measured breaking stress, which indicates that the application of intensity stabilisation technology can improve the statistical strength of fused silica fibres by tightening the spread of values. As the aLIGO detectors upgrade plan (A+) proposes to use thinner fibres, it is essential to enhance the performance of fused silica fibres.