How a Polarimeter Works
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Polarimeters are used to measure the polarization of transverse waves as they exit an object. This almost always refers to the way light refracts as it enters and leaves a transparent object, such as a type of glass, crystal or film. A sample of the transparent material is usually needed, especially with traditional polarimeters that were made with a slot to hold the sample material. Polarimeters can be used to discover many different types of optical features that materials may have, which is useful when exploring the properties of new crystals or measuring the purity of refractive materials.
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When light enters a transparent object, it refracts. Since no object is fully "transparent," the electromagnetic waves are always slightly bent as they pass through. They can also be split apart in many different ways. Polarimeters measure just how much the light is changed to find out the object's specific properties.
These polarization properties were first discovered in the 1800s and were soon followed by the first working polarimeters. These first devices used various plates of glass and a light source to examine how light refracted through a sample slide that was placed into the polarimeter. Some type of analog meter was also attached to more correctly measure the polarization of the light waves.
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Modern polarimeters used a different and much more specific process. A laser is directed through the slide of the object being measured, which is then directed through a series of lenses and very precise detectors that sense how electrons and photons react. These modern devices measure not only polarization but also circular polarization, optical rotation, and the scattering of the light.
Modern-day polarimeters are also used to measure liquid solutions. These solutions are placed in a small tube and then inserted into the device, which shoots the laser and measures how the electrical field of the light waves change. Monochromatic light will be beamed through and generally produce only one of the possible planes for the light to pass through. If the solution has no effect on the light, it considered optically inactive and there will be no change to the angle of the light. If the solution is active (and nearly all solutions will have some effect on light as we see it), then the polarimeter will read a specific angle at which the light is refracted.
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