Thin Film Interference
Thin Film Interference. Soap Film – Why Color? iridescence.
Dec 29, 2015
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Thin Film Interference
Soap Film – Why Color?
iridescence.
t
Thin Film Interference
Some light reflects off top layer, some off bottom layer.
If crest meets trough destructive interference
If crest meets crest (trough meetstrough) constructive interference
If remove (by destructive interference) a color from white light, will see the complementary color.
ex., if yellow light is cancelled, will see blue
Thin Film
What determines the color seen?
Film material (n) and thickness (t)Angle viewed at
(assume light strikes perpendicular)
t
extra distance (ABC) = 2t
Both rays
One ray
1λ, 2λ, 3λ, …
½λ, 3/2 λ,
5/2λ,…
phase shift
2t
Both rays
One ray
1λ, 2λ, 3λ, …
constr. inter.
destr. inter.
½λ, 3/2 λ,
5/2λ,…
destr. inter.
constr. inter.
phase shift
2t
λ is the wavelength in the film
λair
λn = --- n
A soap bubble (n = 1.35) appears green (λ = 540 nm) at the point on its front surface nearest the viewer. What is its minimum thickness?
1.0 x 107 m
Iridescent Paint
Stealth Bomber
Eliminate radar through thin-filminterference
Anti-Reflective Coating
Coated lens reduces reflectionsthrough thin-film interference.
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