Question

A glass lens, nglass = 1.52, has a 140 nm thick antireflective film coating one side, nfilm = 1.37. White light, moving through the air, is perpendicularly incident on the coated side of the lens. What is the largest wavelength of the reflected light that is totally removed by the coating?

Answer 1

767.2 nm

Step-by-step explanation:

The optical path for the reflection for the inner surface is:

`Path=2* n_(film)* thickness`

For maximum wavelength, this distance has to be traveled doubled (The ray is normally incident). So,

`\lambda=4* n_(film)* thickness`

Given that:

`n_(film)=1.37`

Thickness = 140 nm

So, wavelength is:

`\lambda=4* 1.37* 140\ nm`

Wavelength is 767.2 nm