. Alens is coated with thin films of transparent substance MgF2 (n = 1.38) to reduce reflection from glass surface. How thick a coating is needed to produce minimum reflection at center of visible spectrum (λ = 550nm)?
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The change in phase due to the optical path length of the light inside the film should be equal to π. Let t = thickness of the transparent film.
So total optical path length = λ/2 = n * t + n * t inside the film for the reflected ray.
The reflected rays from both surfaces of the film will be in opposite phase. So the transmitted rays go through without destructive interference.
t = λ/(4n) = 550/(4*1.38) = 99.64 nm
Thickness is t or multiples of t.
So total optical path length = λ/2 = n * t + n * t inside the film for the reflected ray.
The reflected rays from both surfaces of the film will be in opposite phase. So the transmitted rays go through without destructive interference.
t = λ/(4n) = 550/(4*1.38) = 99.64 nm
Thickness is t or multiples of t.
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