Structural adhesives for bonding optics to metals: a study of optomechanical stability

摘要

With so many new adhesives available, characteristics affecting performance are not always well-defined. The user often selects an adhesive based on a single property and later finds his application compromised. This is an effort to study relevant properties of several different structural-type adhesives. The bonding geometry will utilize three types of glass (fused silica, BK-7, and Pyrex) bonded to metal mounts. The mounting geometry will include five different design approaches. These designs will investigate: face bonding, counter-bored mounts, edge bonding, and a flexure mount. The three metals selected (aluminum, titanium, and invar) are not only common to the industry but often used for matching the Coefficient of Expansion to the optical glass. Each optical flat will have its reflective surface used as a reference for angular stability. The adhesives selected will compare more traditional epoxies with one-part Ultraviolet Light (UV) cured products. The obvious advantage of the UV-cured adhesives is the instant cure on-demand. Several adhesives have been selected for differing properties including: viscosity, cure temperature, CTE, modulus of elasticity, out-gassing, and shrinkage upon cure. Discussion will compare each adhesive, its properties, and ease of use. Angular stability will be monitored as a function of: pre vs. post cure, accelerated life testing, thermal exposure, and vibration/shock exposure. Some discussion will be included on the Wavefront Distortion and Stress Birefringence.