RESEARCH ON OPTICAL CONTACT BONDING

The adhesion of optically polished surfaces-optical contact-was investigated both under room conditions and ultrahigh vacuum with the twofold objective of determining the adhesion mechanism and its characteristics and extending the technological applications. It is shown that optical contact adhesion occurs readily under ultrahigh vacuum, thus demonstrating that the widely held liquid layer theory is not complete. Adhesion mechanisms are discussed, and it is concluded that London dispersion forces are responsible for the adhesion under ultrahigh vacuum. For optical contacts made under room conditions, surface tension of a liquid probably also contributes. It is shown that optical contact techniques can be used to obtain extremely efficient transducer-sample bonds for gigacycle ultrasonic work. Reflections as low as 1 of the incident acoustic power were obtained at 3 GC and 9 GC. Techniques for making such bonds are discussed. It is pointed out that the incorporation of evaporated metal films should enhance the properties of optical contact bonds and eliminate some practical difficulties. The design and development of a high vacuum evaporator are described.