1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Thin Film Interference

  1. Dec 8, 2009 #1
    1. The problem statement, all variables and given/known data
    What is the thinnest film of a coating with n = 1.43 on glass (n=1.52) for which destructive interference of the red component (660 nm) of an incident white light beam in air can take place by reflection?


    2. Relevant equations
    2t = m*lambda?


    3. The attempt at a solution
    There really is none. Honestly I have been reading through the book for like an hour and trying to figure out what everything means but I just don't understand what to do at all. Any help at all is really appreciated. This just doesn't make sense to me :confused:
     
  2. jcsd
  3. Dec 8, 2009 #2

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    The purpose of the coating is to create two reflecting surfaces separated by a small distance (some light will always reflect when it passes from one medium into another with a different index of refraction). If this distance is 1/4 of a wavelength of the incident light, the light reflecting off the coating/lens surface destructively interferes with the light reflecting off the air/coating surface (ie the wave reflected from the coating/glass boundary is a 1/2 wavelength out of phase with the light reflecting from the air/coating boundary). This reduces light reflection and increases the amount of light passing through the lens.

    So you have to create a layer of thickness equal to 1/4 of the wavelength of the light.

    AM
     
  4. Dec 8, 2009 #3

    ehild

    User Avatar
    Homework Helper
    Gold Member

    The thickness of the coating should be 1/4 of the wavelength inside the layer. The wavelength changes when the light enters from air to an other material with refractive index n. If the wavelength of the incident light is [itex] \lambda_0 [/itex], that in the material is [itex] \lambda=\lambda_0/n [/itex]. So the thickness of the antireflecting coating should be [itex] d=\lambda_0/(4n)[/itex].

    ehild
     
  5. Dec 8, 2009 #4
    Thank you very much. That helped me out a lot. I couldn't not figure that out at all.

    Thanks again.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Thin Film Interference
  1. Thin film interference (Replies: 3)

Loading...