Hydroxide-Bonding Strength Measurements for Space-Based Optical Missions

Optical contacting has long been used in interferometric experiments both on the ground and in space-based missions. Its optical clarity makes it an ideal method to joint materials of comparable coefficients of thermal expansion. Once the two pieces are bonded, they are commonly broken through thermal or vibrational cycling. Unfortunately, larger bond areas are needed for the bond to form appreciable strength, which often excludes it from being used in complex optical bench designs in space-based missions. Another method, known colloquially as hydroxide bonding, has shown to have superior strength to optical contacting using smaller bonding areas. In addition, the hydroxide bonding process will work on several materials that do not need to meet the stringent polishing requirements of optical contacting. These properties make hydroxide bonding suitable for complex optical bench designs that can withstand the large accelerations encountered during launch conditions for use in space-based missions. In this paper, we report on shear strength measurements of BK7-to-BK7 hydroxide bonds as well as present new results for BK7-to-silicon carbide and BK7-to-Super Invar bonds.