Ch 37 Thin Film Interference

thin-film interference

at a boundary between two materials part of a light wave

is reflected and part is refracted

n1 < n2

slower

n1 > n2

faster

at a boundary between two materials part

of a light wave is

reflected and part is refracted

examples of thin-film interference...

color of soap bubble \n spectrum created by thin film of oil on water blue color of butterfly wing \n Newton’s rings

eyes of nocturnal animals (cat’s eyes)

antireflective coating on glassdestructive interference for middle of visible spectrum

antireflective coating on Stealth Bomberdestructive interference for radar waves

photograph vs Hologram

a 2-D record of a 2-D image

a 2-D record of a 3-D image

diffraction

interference of light through a single opening interference of light around a small object

the bending of light that occurs around the edge of an object

diffraction L

distance from aperture to screen

diffraction examples

through a single slit

around a strand of hair

through a small pinhole

around blood cells \n around edge of razorblade

shadow of pinhead

polarization

can exist only for transverse waves. Since Electromagnetic waves are traverse, they can be polarized.

Polarized light will not be transmitted through a polarized film whose axis is 

perpendicular to the polarization direction.

selective absorption polarization examples

polaroid filter

–camera filter

–3-D movie filming, projection, viewing • liquid crystal display (LCD)

Polarization by Reflection

When an unpolarized light beam is reflected from a surface, the reflected light may be

– Completely polarized – Partially polarized– Unpolarized

The polarization depends on the angle of incidence.

* –  If the angle is 0°, the reflected beam is unpolarized.
* –  For other angles, there is some degree of

polarization.
* –  For one particular angle, the beam is completely polarized.