6H35.40 - Quarter and Half Wave Plates

Code Number:
Demo Title:
Quarter and Half Wave Plates
Optical Rotation, Linear to Circular Polarization
Area of Study:
Quarter and Half Wave Plates, Interference and Regular Filters, Cardboard Mask with 2" X 2" Hole, Polaroid Plates, Overhead Projector, Pasco Sodium Light Source, and Green Laser Pointer - Optional.

Place the mask on the overhead and then place the # 57 interference filter in the square hole.  This will give you a very narrow band of wavelengths centered around 560 nm. (see the spectrograph done with the Ocean Optics spectrometer that is with the filter).  Place one Polaroid directly on top of the filter and then place the other Polaroid as shown and turn it until you achieve extinction.  Place the 1/4 wave plate at 45 degrees to the filter and observe that no matter how you turn the top Polaroid now you can not get extinction.  In fact the intensity of light you see should be almost the same throughout the rotation.  The 1/4 wave plate has circularly polarized the light coming through the bottom Polaroid.

Using the same filter and Polaroid setup as above rotate the top Polaroid to achieve extinction.  Place the 1/2 wave plate at 45 degrees to the filter and now note that you have to turn the top Polaroid 90 degrees to achieve extinction (basically you can put the 1/2 wave plate in at any angle to the filter and observe that you will have to rotate the top Polaroid twice that angle to achieve extinction).

You can also use the Pasco sodium light as your light source instead of the overhead projector.  It will also help if you use the # 57 filter in this instance.

There is also some homemade 1/4 plates made out of tape.

NOTE: These work at a 650 nm wavelength and because of this, they are not as visible as the plate described above.

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