Lesson: Thin Film Interference
In this lesson, we will learn how to calculate the thickness of thin films that produce interference by the reflection of light from the layers' surfaces.
Sample Question Videos
Worksheet: 20 Questions • 1 Video
What are the smallest nonzero thicknesses of a film of soapy water on Plexiglas that strongly reflects 520 nm wavelength light when illuminated perpendicularly by white light? Use a value of 1.33 for the refractive index of the soapy water.
As a soap bubble thins, it becomes darker because the path length difference between reflected light waves becomes small compared with the wavelength of light reflected by the bubble, and the light waves are phase-shifted at the top surface of the bubble. If the bubble becomes dark when the path length difference is less than one-fifth of the wavelength, what is the thickest the bubble can be and still appear dark at all visible wavelengths? Use a value of 575 nm for the reflected light’s wavelength and a value of 1.33 for the refractive index of the bubble.
What is the minimum thickness of the film?
If 380 nm is the longest wavelength for which an intensity minimum occurs, what is the nearest wavelength to 380 nm that produces an intensity minimum?