Effects of curing, temperature, pressure, and moisture on the surface-figure of a high-precision bonded mirror

Adhesive bonding is widely used in the assembly of high-precision optomechanical products. However, of the curing and relaxation behaviors as well as environmentally sensitive features of adhesives, the surface-figure accuracy of bonded mirrors is often attenuated, which greatly degrades the performances of the optomechanical system. This paper developed a comprehensive finite-element model for understanding the evolution of surface figure in a high-precision bonded mirror. For the used optical adhesive, its cure kinetics was experimentally examined by differential scanning calorimetry and then modeled based on a modified Kamal kinetic model, and its mechanical behaviors were described by a viscoelastic constitutive model including temperature, moisture, and degree of cure. Additionally, time-temperature/moisture/curing superposition principles for the adhesive were experimentally determined and embedded into the constitutive model. The comprehensive finite-element model was verified and then applied to simulate the surface-figure evolution of the bonded mirror. The effects of environmental factors, such as temperature, environmental pressure, and moisture, on the surface-figure accuracy and stability were further understood.