Time-evolution of NIR absorption in hydroxide-catalysis bonds

Hydroxide-catalysis bonding is a powerful precision jointing technique. It is used to construct opto-mechanical systems, e.g. in gravitational-wave detectors or satellite-based telescopes, and for optical applications such as high-power laser-crystal assemblies or transmissive optical components. Here we present studies of the optical absorption of such a bond over a period of 38 days after bonding. We find significant absorption at 1550 nm and 2000 nm, while it is negligible at 1064 nm. We show a factor of four reduction in absorption over the observed period, which could increase the tolerable power in transmissive bonded optics. Based on the absorption ratio found at different wavelengths, we conclude that the absorption is most likely dominated by water migrating out of the bond by two mechanisms.