What is polarized light?

x

Looking "head-on" we only see the blue arrows up & down

y

z

x

y

z

• Light is polarized if the light wave and electric force field arrows remains in the same plane– The (blue) arrows must be

perpendicular to the ray• This is a light ray traveling in the z-

direction and polarized in the y-direction

• Here is a light ray traveling in the same direction but polarized in the x-direction

• We see the polarization in the x-y plane, looking at rays head-on– The blue arrows point up and down or

left and right, stacked up behind one-another.

y

x

What is unpolarized light?

• For unpolarized light the plane of polarization keeps jumping around– But the electric field arrows

remain perpendicular to the ray (direction of travel of the wave)

– We visualize this in the x-y plane (looking into the ray) as shown at right• The many crossed double

sided arrows are the symbol for unpolarized light

• See Physics 2000

x

y

z

electric force arrows jump around while remaining perpen-dicular to the ray

wave travels in z-direction

http://www.colorado.edu/physics/2000/index.pl

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Polarization

• Polarization is a phenomenon of light that is used in sun-glasses, photography and 3-D movies.

• Play with the two polarizing filters for a few minutes and note what is happening and see if you can think of any reasons for it.

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Polarization Hint

• Light vibrates in all directions.• A polarizing filter acts like a picket fence. It

only lets certain direction vibrations pass through it.

• Therefore, if you pass light through two of them you can completely block the light from passing through.

• HOW?

For light: Polarizers (Polaroid films)

Same story:

Polarization

Polaroid sunglasses (and camera filters) take advantage of this effect to block bright reflected light from the snow, beach, road,

water, sky, etc.

• When you wear polaroid sunglasses they block light polarized in the plane of your two eyes– When your head is vertical this is the horizontal plane– Since reflected light from the ground or scattered light from

the sun are mostly polarized in the horizontal plane such light is mostly blocked

• Demo with polaroid filters– The first filter blocks one polarization and lets through the

other (perpendicular) one– The second blocks more and more of the remaining polarized

light as its axis is rotated so as to permit only the polarization blocked by the first

– When the axes of the two polaroid filters are at right angles to each other no light comes through

Polarization Photography

Reduce Sun GlareReduce ReflectionsDarkens SkyIncrease Color SaturationReduce Haze

Polarization Photography

Without Polarizer With Polarizer

• Provides better Color Saturation

• Darkens the sky

Polarization Photography

Without Polarizer With Polarizer

Polarization Photography : Scattering

De-hazedHaze

Polarization Photography : Wide Angle Lenses

Vignetting of the Sky

Polarization Photography : Reflections

Reduce Reflections

Polarization Photography : Reflections

Reduce Reflections

Aqua-polaricam

Y. Schechner & N. Karpel, underwater imaging

Polarization Photography : Underwater

• Underwater pipelines and communication

• Offshore structures

• Underwater ROV/AOV

• Offshore drilling rigs

• Vessel inspection

• Recreational photography

• Marine archaeology

• Marine biology

• Underwater mapping

Light as Plane Waves

•Polarized Wave: Has only one preferred orientation.

•Un-polarized Wave: Has no preferred orientation. or has all orientations.

•Partially polarized wave: Has preferred orientation but has energy in other orientations as well.

180 o

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Crossed Polarizers

Polarizer Puzzle

If crossed polarizers block all light, why does putting a third polarizer at 45° between them result in some transmission of light?