Thin Film Interference

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Thin Film Interference
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Soap Film Why Color?
iridescence.
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Reflection and Phase
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t
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Thin Film Interference

• Some light reflects off top layer, some off
  bottom layer.

If crest meets trough ? destructive interference
If crest meets crest (trough meets trough) ?
constructive interference
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If remove (by destructive interference) a color
from white light, will see the complementary
color.
ex., if yellow light is cancelled, will see
blue
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What determines the color seen?
Thin Film
Film material (n) and thickness (t) Angle viewed
at
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(assume light strikes perpendicular)
extra distance (ABC) 2t
phase shift
Both rays One ray
1?, 2?, 3?,
½?, 3/2 ?, 5/2?,

2t
t
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phase shift
Both rays One ray
1?, 2?, 3?, constr. inter. destr. inter.
½?, 3/2 ?, 5/2?, destr. inter. constr. inter.
2t
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? is the wavelength in the film
?air ?n --- n
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A soap bubble (n 1.35) appears green (? 540
nm) at the point on its front surface nearest the
viewer. What is its minimum thickness?
1.0 x 107 m
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(No Transcript)
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Iridescent Paint
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Stealth Bomber
Eliminate radar through thin-film interference
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Anti-Reflective Coating
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Coated lens reduces reflections through thin-film
interference.