Mechanical loss of a hydroxide catalysis bond between sapphire substrates and its effect on the sensitivity of future gravitational wave detectors

Abstract

Hydroxide catalysis bonds are low mechanical loss joints which are used in the fused silica mirror suspensions of current room temperature interferometric gravitational wave detectors, one of the techniques which was essential to allow the recent detection of gravitational radiation by LIGO. More sensitive detectors may require cryogenic techniques with sapphire as a candidate mirror and suspension material, and thus hydroxide catalysis bonds are under consideration for jointing sapphire. This paper presents the first measurements of the mechanical loss of such a bond created between sapphire substrates and measured down to cryogenic temperatures. The mechanical loss is found to be $0.03\ifmmode\pm\else\textpm\fi{}0.01$ at room temperature, decreasing to $(3\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}4}$ at 20 K. The resulting thermal noise of the bonds on several possible mirror suspensions is presented.