Polarimeter data book-basic principles of polarimeters

Is it a particle or a wave? Is it both or maybe neither of them? Light has the properties of particles and of waves. It’s a phenomenon that can’t be fully explained just by asking whether it’s a particle or a wave.
Light has long fascinated people, and it has plagued many scientists in their attempts to unlock its mysteries.
Optical rotation is a phenomenon of light where light passes through a substance and rotates depending on the substance.
Substances and compounds that have properties that cause light to turn are called "optically active" substances. The light rotates to the right or to the left, depending on the substance, as well as at different angles. From its angle of rotation we can deduce certain things about a particular substance. Polarimeters are used to measure the angle of rotation.

Principles of measurement

The light exhibits a "wavelike" characteristic as it oscillates during propagation. When this wavelike light passes through a substance, a phenomenon occurs in which the direction of the oscillating wavelike light rotates. This is the optical rotation of the light.
On this basis, let’s try to explain optical rotation with an easy-to-understand metaphorical illustration. Draw a wavy line on a long piece of paper. Hold the paper at both ends in the middle with your fingers. Rotate it around in all possible directions. This oscillating wave that propagates in many directions, a deeply complicated phenomenon interwoven with other matter, is natural light. This is the normal state of the light.

The angle of rotation of the light cannot be measured in this condition. Oscillating light waves propagate in any direction, so it is impossible to determine which wave passes through a substance and to what degree it is rotated.
Therefore, light, which propagates in many directions and oscillates along its path, must be limited to propagation in one direction. To achieve this, light is passed through something called a "polarizer". A polarizer has a grid-like pattern arranged in a complicated alternating shape of lines through which light does not pass and of recesses through which light does pass. The light is stopped by the polarizer, which allows only a single light wave to pass through, propagating in a particular direction. This is called "polarized light".


When two polarizers are placed in sequence and only one is rotated, an angle is formed that completely blocks out the light. This is because the light that passed through the first polarizer and was confined to a single wave moving in one direction is blocked by a second polarizer at a different angle.
By rotating the polarizer (the second polarizer in a polarimeter is called the "analyzer") and finding the angle at which the polarized light passed through, or. of the angle at which it was blocked, it is possible to measure the angle at which the light passed through a substance (the angle of rotation). Polarimeters apply this principle to measure the angle of rotation of a substance.


Polarimeters are instruments used to measure the angle of optical rotation of light. In general, polarimeters have mechanisms such as a light source and a polarizer. The light coming from the light source passes through the polarizer, and the direction of the light wave is restricted. The angle at which the light rotates is measured as it passes through the substance.
If, when measured, the plane of vibration facing the light source appears to rotate clockwise, it is dextrorotatory. If it appears to be rotating counterclockwise, it is counterclockwise. "Dextrorotating" comes from the Latin word "dextro", which means "right". The English "d-rotary" can also mean clockwise. "Levorotating" comes from the Latin word "levo," which means "to the left". counterclockwise rotation is also called "l-rotatory". The system for designating optical isomers (enantiomers), either d- or l-, is derived from these words.
Polarimeters are mainly used in the sugar and pharmaceutical industries. In the sugar industry, polarimeters are used to determine the type of sugar or to determine purity. In the world of pharmaceuticals there are many cases where chemical compounds can be subordinated to certain standards, depending on the angle of rotation. Polarimeters are used to perform investigations such as z. B. to carry out the determination of the nature of the substance.

Polarizers for daily practical use

In terms of polarimeters and the optical rotation of light, the word "polarizer" sounds like a difficult concept to imagine. However, surprisingly, polarizers are also used in various places in daily life.

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