Physlet Illustration: Thin Film Interference
Air                                   Glass Lens

 

 

Interactive Help
on      off
Index of Coating =             Thickness of Coating = nm

In this simulation, a nonreflective coating is applied to the front of a camera lens of index of refraction 1.52.  What combination of thickness of the coating (variable between 0 and 600 nm) and index of refraction of the film (variable between 1 and 3) minimizes reflection and maximizes transmission for yellow-green light (565 nm)?    

Hints:

  1. Begin with a film thickness of 0 nm.  The index doesn't matter.  Note how much light is reflected.
  2. Set the thickness to the default value of 300 nm and try adjusting the index of refraction.  What happens when it is 1?  When it is 1.52?  When it is greater than 1.52?  What is the "best" range of  values to reduce reflections?
  3. Set the index to a value in the middle of the "best" range.  Adjust the thickness.  How does the thickness affect the amount of light reflected?
  4. Why are these films often called quarter-wave coatings?

Reference

See Walker, Sections 28-3

Illustration written by Chuck Niederriter