Pendulum Mode Thermal Noise in Advanced Interferometers: A comparison of Fused Silica Fibers and Ribbons in the Presence of Surface Loss

TL;DR

This paper compares fused silica fibers and ribbons for suspensions in gravitational wave detectors, analyzing how surface loss and physical parameters influence thermal noise levels, with ribbons potentially offering significant noise reduction.

Contribution

It provides a detailed comparison of fiber and ribbon suspensions, highlighting how surface loss and physical parameters affect thermal noise in advanced interferometers.

Findings

Fused silica ribbons can significantly reduce pendulum thermal noise.

Surface loss limits the minimum achievable noise level.

Cylindrical fibers remain a viable alternative despite higher noise levels.

Abstract

The use of fused-silica ribbons as suspensions in gravitational wave interferometers can result in significant improvements in pendulum mode thermal noise. Surface loss sets a lower bound to the level of noise achievable, at what level depends on the dissipation depth and other physical parameters. For LIGO II, the high breaking strength of pristine fused silica filaments, the correct choice of ribbon aspect ratio (to minimize thermoelastic damping), and low dissipation depth combined with the other achievable parameters can reduce the pendulum mode thermal noise in a ribbon suspension well below the radiation pressure noise. Despite producing higher levels of pendulum mode thermal noise, cylindrical fiber suspensions provide an acceptable alternative for LIGO II, should unforeseen problems with ribbon suspensions arise.