Pendulum mode thermal noise in advanced interferometers: a comparison of fused silica fibers and ribbons in the presence of surface loss

The use of fused-silica ribbons as suspensions in gravitational wave interf erometers can result in significant improvements in pendulum mode thermal n oise. 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 dampi ng), and low dissipation depth combined with the other achievable parameter s can reduce the pendulum mode thermal noise in a ribbon suspension well be low the radiation pressure noise. Despite producing higher levels of pendul um mode thermal noise, cylindrical fiber suspensions provide an acceptable alternative for LIGO II. should unforeseen problems with ribbon suspensions arise. (C) 2000 Elsevier Science B.V. ALI rights reserved.