Question

A nonreflective coating (n = 1.30) covers the glass (n = 1.52) of a camera lens. Assuming that the coating prevents reflection of a specific wavelength (vacuum = 505 nm), determine the minimum nonzero thickness that the coating can have.

Answer 1

It is obvious that there are phase changes for the reflection of the light incident from the air (n=1) to the coating(n=1.32), and for the reflection of the light incident from the coating(n=1.30) to the glass (n=1.52).

Hence these two phase change cancel one another. We only need to make the traveling of the light inside the coating to be of half the wavelength.

That is: the minimum nonzero thickness of the coating is: {Lemda}film ={Lemda}air/4n

=505 nm/(4n) = 505 nm/(4*1.30) = 97nm

Hope it will help you.