What Is a Monochromator?

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  • Written By: M. McGee
  • Edited By: Lauren Fritsky
  • Last Modified Date: 07 October 2019
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A monochromator is a device that can transmit one wavelength of visible light, non-visible light or radiation totally by itself. Unlike many light-, energy- or radiation-transmitting devices, a monochromator transmits a pure wavelength. Most transmission devices will transmit a main form of energy, but it will often be distorted my nearby bands, such as adjacent colors of visible light or thermal interference. These devices have a limited number of uses, but within those uses, they are essential. Certain areas of optics, cosmological research and chemical analysis use these devices in a huge range of experiments and tests.

The uses of a monochromator usually come down to aiming a beam of specific energy at a sample and measuring the resulting emitted light. While this seems very simple, it is actually extremely useful in determining the composition of the sample, such as density and chemical makeup. These processes are also used in designing and testing optical systems that will operate in very specialized or difficult conditions. By knowing the way energy will interact with the system, it is possible to anticipate and account for certain optical anomalies.


The difference between a monochromator and other devices that are able to transmit clean energy is the range at which it can do it. In most cases, these devices can actually transmit several different types of energy by simply adjusting the internal structures of the machine. This is especially common in the ones that transmit visible light; they can often display a large portion of, or even the entire, color spectrum.

In the visible light forms of monochromator, there are several methods used to make the light, but reflecting light bounced through prisms is one of the most common. At one end of the device, a normal visible light is generated which contains all the different wavelengths of light. By selectively bouncing that light off of prisms and reflectors within the machine, a specific light color can be separated from the rest of the light. This will then shine out, typically via a slit or a lens.

The angles, heights and locations of the prisms and reflectors determine the exact wave separated from the full spectrum of light. By adjusting these objects, the monochromator can change which light it sends out. In older machines, these adjustments were typically done by hand, but newer machines have all the internal parts connected to servers. A researcher can simply determine the frequency they want active and dial it into the machine’s control system.


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