Question

Interference Colors Question

Describe in words why a coating of thickness λ/4 on a high quality optical lens increases the intensity of transmitted light.

Answer 1

A coating of increases the optical path length of the light which gets transmitted. So, increasing the path length gives rise to path difference between light getting reflected from upper and lower interface. This thickness can be tuned to cause destructive or constructive interference of reflected light.

The minimum thickness required for destructive interference of reflected light is

this implies that no reflection is achieved for this thickness. Therefore, maximum amount of light is transmitted through the lens at the same thickness and so a thickness of on the optical lens increases the intensity of transmitted light.