Interference Condition for Thin Films

Thin films
Fabry-Perot geometry
Snell's law
Index

Interference concepts
 
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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.

Calculation for oil film
Air gap example
Index

Interference concepts

Reflection concepts
 
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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.

Oil film example
Index

Interference concepts

Reflection concepts
 
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