Thin films

This applet illustrates the physics behind antireflective coatings.

The purpose of antireflective coatings is to reduce the amount of light reflected off of the front of a lens, thereby maximizing the amount of light entering the optical instrument.

The basic idea is that the reflection of the light off of the optical instrument really is the superposition of the light reflected off of the front of the coating and of the light reflected off of the back of the coating. The coating is designed so that - as much as possible - the superposition is destructive, with the result that as little as possible of the light is reflected and as much light as possible enters the optical instrument.
However, for a given coating material and thickness, totally destructive interference can only be achieved for certain wavelengths and angles of incidence.

This applet allows the user to choose among two coating materials and to adjust the angle of incidence as well as the coating thickness. The red line is a visual aid to help the user determine the relative phases of the rays reflected off of the front and back of the coating.

This applet correctly shows the following:

This applet does not show the following: