1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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. Nov 29, 2009 #1
    1. The problem statement:

    A wavelength (λ)550 nm light ray traveling thru a viscous medium n1= 1.46 strikes a a crystal n3=1.5 protected by a film n2=1.25.

    2. Relevant equation:

    How can I determine the min thickness of the antireflective coating used to minimize the reflection of the incident light?

    3. The attempt at a solution
    I think I can determine it by using
    2t+0.5λ1+0.5λ3= (m+0.5)λ2 where m=1 and then solving for t.

    Any guidance would be greatly appreciated.
  2. jcsd
  3. Nov 29, 2009 #2


    User Avatar
    Homework Helper

    Welcome to PF, Geekio.
    I waited an hour and a half to post because I just don't understand this question.
    To prevent reflection, you normally use a coating with index of refraction midway between the two media. In this problem your media are n = 1.46 and n = 1.5 while your coating is 1.25. At the 12 boundary your index is decreasing while at the 13 boundary it is increasing, so your reflections will be out of phase half a wavelength for starters. Oh, I think I see it . . . if the coating is half a wavelength thick and traversed twice, that is a total of 1.5 wavelengths and you'll get destructive interference. Clever! Never heard of it before but it ought to work.

    So the answer is 0.5 wavelengths for the light in n = 1.25. I guess you'll have to figure out the frequency of that light from the information given at n = 1.46, then use that frequency to calculate the wavelength at n = 1.25.
  4. Nov 30, 2009 #3
    thank you very much
  5. Dec 3, 2009 #4
    hi ...i prepared thin film samples by spray pyrolysis technique but thier surface arent smooth ..can anyone tell me how can i make it smooth ???plz
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Thin Film Interference Date
Interference in thin films Dec 11, 2017
Maximum/minimum reflection | Thin-film interference Nov 12, 2017
Thin film interference on water Oct 15, 2017
Thin Film Interference Sep 18, 2017