Suspension upgrades for future gravitational wave detectors

To further increase the sensitivity of the aLIGO detectors, upgrading the monolithic fused silica suspension is considered for an upgrade option: a higher stress in the fibre and a longer final stage. One of the challenges for this upgrade will be producing thinner and longer fibres that can hold the test mass safely. Since laser power fluctuations during the fibre fabrication process can produce potentially weak fibres, we present a laser intensity stabilisation technology for fused silica fibre fabrication that was investigated to allow further improvements on fibre production consistency which could be applied to aLIGO upgrades. Fibres fabricated with this new technique showed 30% decreased standard deviation of breaking stress, which indicates that the application of intensity stabilisation technology can improve the statistical strength of fused silica fibres. Combined with a longer polishing duration, the average breaking stress also improved by 9%. As higher stress in the fibre and the longer final stage can improve the detector’s sensitivity, these enhanced technologies will enable us to fabricate thin and robust fibres that can achieve future suspension upgrade requirements