Interference Condition for Thin Films

Reflection Phase Change

Reflected light will experience a 180 degree phase change when it reflects from a medium of higher index of refraction and no phase change when it reflects from a medium of smaller index. Note below that the reflection when traveling from air at n=1 to oil at n = 1.4 experiences the phase change, but from oil to water at n = 1.33 there is no phase change. This phase change is important in the interference which occurs in thin films, the design of anti-reflection coatings, interference filters, and thin film mirrors.

Reflection Phase Change

Reflected light will experience a 180 degree phase change when it reflects from a medium of higher index of refraction and no phase change when it reflects from a medium of smaller index. This phase change is important in the interference which occurs in thin films, the design of anti-reflection coatings, interference filters, and thin film mirrors.