A polarimeter measures the amount of light received at a specific point by measuring the refraction of light through a medium. It has a wide range of applications in chemistry and physics, including determining the purity levels of drugs and identifying polymer concentrations in the plastics industry. The laser polarimeter is useful for monitoring degenerative eye conditions such as glaucoma.
A polarimeter is a scientific instrument for measuring the amount of light received at a specific point. This depends on which direction or polarization the various light waves may have in reaching the source. The polarization process of light was first discovered in 1808 by Etienne-Louis Malus, a French physicist, while one of the first functional polarimeters to measure the effect was made by Jean-Baptiste Biot, another French physicist, in 1816 They were continually perfected until the mid-1800s, when they reached a level of sophistication that remained largely unchanged until the late 20th century. The progress of polarimeter design from the 1920s onwards led to the digital polarimeter and automatic polarimeter which are computer controlled and have electronic readings.
Because a polarimeter measures the refraction, or bending of light through a medium, they are largely tools of chemistry and physics. The samples used to measure the effect must be partially transparent. They come in a variety of shapes and sizes, but the basic principle is the same. A beam of unpolarized light is reflected by mirrors and then refracted through solid crystals or transparent liquid samples which decompose it into polarized light.
Because the light waves are polarized in a basic polarimeter, they are channeled through a tube 4 inches (10 centimeters) in diameter that contains the chemical being studied. If the compound has polarizing properties, the brightness of the light will decrease as its exit angle from the tube varies. This angle is then determined by rotating the analyzer axis at the end of the tube. If the change in angle is considered positive, or to the right, it is called dextrorotatory, and if it is to the left, it is called levorotatory. The magnitude of the angle of rotation is determined both by the length of the tube and by the type and concentration of the compound through which the light is passed, known as an enantiomer.
In fine-tolerance applications, such as ophthalmology, the laser polarimeter or optical polarimeter is integrated into an ophthalmoscope and uses a near-infrared laser to determine the cornea’s ability to compensate for polarized light. This is useful for monitoring degenerative eye conditions such as glaucoma. The results are then analyzed using statistical software to try to predict the onset of glaucoma before physical symptoms are present in the patient.
Because many compounds exhibit rotation of the light passing through them, the polarimeter has a wide range of applications in the pharmaceutical, food and chemical industries in general. They are routinely used to determine the purity levels of drugs such as antibiotics, the concentrations of sugar and flavoring molecules in various food products, and to identify polymer concentrations in the plastics industry.
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