Optimum Band Width for Two Layer Anti-Reflection Films

To determine the reflection from a two layer anti-reflection film on glass the ideas and terminology of network analysis are introduced. Those parts of network theory to be used are briefly reviewed. This theory is shown to provide a clear physical picture of the field changes which occur with varying film parameters. It is shown that there is a relation connecting these parameters which defines an optimum design for best bandwidth. This design yields a reflection curve having two points of zero reflection and in a typical case gives less than 0.005 reflectivity over a range extending well beyond the visible spectrum at both ends. If, because of physical limitations, the optimum proves to be unattainable, then the conditions for closest approach are outlined.