S.Rowan, G. Cagnoli, J.Hough, M. Fejer, E. Gustafson, R. Route

An important limiting noise source for all long baseline interferometric gravitational wave detectors will the thermally excited motion of the test masses and their suspensions, the level of this depends on the loss factors of the materials used in the suspension construction. Measurements on fused silica suggest it to be an excellent and practical material for the test masses and their suspension fibers, and the technique of hydroxy - catalysis bonding makes the construction of a monolithic final suspension stage a reality. In this talk a review of experimental results relevant to fused silica suspensions will be given, leading to a discussion of what the limiting performance of such suspensions may be in the future.  Extensions of the monolithic concept to include low loss crystalline materials such as sapphire or silicon will also be presented.