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This site contains information on how to make optical polarizers and associated technologies.
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  • Light and all electromagnetic radiation is a wave changing back and forth (oscillating) between ninety-degree (perpendicular) electric and magnetic properties or vectors.  This means that light moves through space as asymmetric left or right handed (chiral) cork screws or helices.

Drag on left and right handed helices to compare them!
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  • Plane polarized light is made by putting together the electric vectors of a left and right handed helix of light to cancel out their magnetic vectors.

     

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    • This flat wave is like shaking a long unplugged electrical extension cord up and down between two rows of brave volunteers.
    • Optical polarizers work like fine slits that only let light in one plane pass through.  This is why they are often called polarizing filters.  Cut slits on a piece of paper to show that a hand like a light wave can only go through in one direction.  Cut two for a later demonstration.   These are the kinds of polarizers we will be making!
       
  • Plane polarized light can be detected by changing the direction or orientation of a second polarizer with respect to the first polarizer to block the transmission or reflection (more later) of any light.  
    • This can be illustrated by crossing two pieces of paper with slits on them and crossing them so that your hand can go through the first "polarizer" slits but not the second.

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    You can demonstrate this:

    • by crossing two polarizers.  One of the polarizers can be an LCD (Liquid Crystal Display) watch or portable-computer screen as illustrated bellow.  Where else can you find polarizers?
    • by looking at light reflected from water, glass, packaging, etc. (called glare) and blocking it out  with a polarizer,  This is how some eye glasses work to improve visibility and safety.  Is all reflected light polarized?
    • Crossing a polarizer in front of your computer.
  • Chiral or asymmetric materials transmit, reflect or "slow" unequal amounts of left and right handed helices to give light in which the net plane of polarization is rotated with respect to the plane transmitted or reflected by the first polarizer.  Since the amount of rotation depends on the amount of material and wavelength, white light can be separated into its spectrum!  This property of chiral or asymmetric materials is called optical activity.

    You can demonstrate this:

     

    • by looking at a sugar solution sandwiched between two optical polarizers.  (Sugar is a chiral material with the given structures.)
      Sugar water under a polarizer.
    • by looking at overhead transparencies sandwiched between two optical polarizers.  You can compare this to looking at other pieces of plastic that are not made of cellulose acetate.
      Watch the image be disappear!
  • Other uses for Polarizers.
    • Polarizers can be used to illustrate where stress is concentrated.  Bridge builders used to use them in order to find the stress points on their bridges. 
    • A polarizer showing the stress of plexiglas.
    • Also, many artists use polarizers.  When used in front of biological material, you can display many different colors as seen below.  Rotate the polarizer in front of the biological material with a light source behind it to display different colors.
    • Packing tape on a CD cover reflects polarized light.
    • Calcite creates a double image when placed over text or other images.  When you use a polarizer, you can view one image at a time by blocking one image out while allowing you to view the other one.
    • Cosmology
    • Lithography

 

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Tuesday, February 14, 2012

jsal at utep dot edu