Anti reflective coatings on lenses use thin film interference

By Allen Kazadi

Anti-reflective coatings on lenses use thin-film interference to eliminate the reflection of a particular color. Suppose a glass lens (ng = 1.55) is covered with a thin film (nf = 1.35) to prevent green light (λ = 521 nm) from being reflected.

a. Write an expression for the minimum thickness the film can have, t.
b. Calculate the minimum thickness, t, in nanometers?


We are given that



\lambda=521 nm=521\times 10^{-9} m

1 nm=10^{-9} m

a.We have to find the expression for the minimum thickness the film can have ,t.

Condition for destructive interference



For minimum thickness m=0

Then, t=\frac{\lambda}{4n}

b.Substitute the values

t=\frac{521\times 10^{-9}}{4\times 1.35}=96.5nm

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