Curing Characteristics of UV Curable Adhesives and Behavior of Cured Optical Component Analyzed by Off-axis Digital Holography

In the curing process of ultraviolet (UV) curable adhesives, an optical mirror glued by UV curable adhesive on a metal plate is moved due to a shrinkage of adhesive film. When the UV-light illuminates the adhesive film, the curing process of the adhesive around the mirror showed the different behavior due to the different illuminating light intensity. This kind of movements due to the curing adhesive causes crucial positional error for the optical devices requiring the precisely controlled location of optics. Therefore, it is important to investigate the shrinkage of the UV adhesive film quantitatively. For the purpose, off-axis digital holographic technique was applied to investigate the movement of the aluminum plate placed on the adhesive film surface in the hardening process. Evaluating the displacement of the plate in the process, it was shown that the adhesive film first contracted, and then expanded due to thermal expansion caused by the exothermic photopolymerization reaction. It was found that the behavior of the hardening adhesive explained the behavior of the mirror fixed by the UV-curable adhesive.