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So I'm having some trouble with this problem.. Is there an equation or is it just a ratio? I'm having so many problems with this one!


What is the minimum thickness of coating which should be placed on a lens in order to minimize reflection of 531 nm light? The index of refraction of the coating material is 1.32 and the index of the glass is 1.57.

  • Physics -

    Read "single layer reflection coatings" at

    You need 1/4 wavelength thickness at a refractive index of 1.32

    At 531 nm and index 1.32, the wavelength of light is 531/1.32 = 412 nm

    The coating thickness should be 1/4 of that

  • Physics -

    that's what i thought, too. but it's not.

    2n(material)t= m*(wavelength/2)

    going from a medium with higher n to lower n, you divide the wavelength by 2.

    thanks for the help, though. i eventually figured it out!

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