A thin film of polystyrene of refractive index 1.49 is used as a nonreflecting coating for Fabulite (strontium titanate) of refractive index 2.409.
What is the minimum thickness of the film required? Assume that the wavelength of the light in air is 450 nm.|||The reflected rays must be 位/2 out of step so that they don't reflect.
There will be a phase shift as each reflection so they cancel out and the only path difference will come from the thickness of the film. And the wavelength will shorten in the film so
位/2 = 碌 . 2 . t
t = 位 / 4碌 = 450 nm / 4 . 1.49 = 75.5 nm
Notice - you don't need the value of 碌 for the titanate but you do need to know that it is more than the value of 碌 for the polystyrene .
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