Monochromators 101

Scanning Digital Mini-Chrom MonochromatorCollecting, altering, and harnessing light is critical to dozens of commercial and scientific processes, ranging from staged entertainment and photography to highly-complex spectroscopy. In some instances, manipulating light is simple – you only need a basic glass lens. But when light needs to be separated into a specific wavelength, or range of wavelengths, a more complex tool is required. That’s where a monochromator comes in. Let us take a look at the essential attributes and functions of this tool, as well as what Optometrics’ monochromators bring to the table.

The basics

Just as its name suggests, a monochromator must isolate, filter, and channel a narrow wavelength band from a given light source, and its users should have the option of adjusting the device to select different bands.

As explained by Nikolai V. Tkachenko in the journal Optical Spectroscopy, white light enters a monochromator through an entrance slit, and is then collected on a focusing mirror before being directed to a diffraction grating. There, the light is dispersed into a spectrum. The diffracted light is then reflected back to the collimating mirror where it is focused so a specific wavelength of light can be directed to the exit slit.

The image above shows how light travels through the common Fastie-Ebert monochromator, one of the two most common monochromator designs. Its counterpart, the Czerny-Turner configuration, essentially produces the same result, but uses two spherical mirrors instead of a single large one.

Common applications of monochromators

Within the field of optical spectroscopy, which studies how light is emitted and absorbed by matter, monochromators are a critical tool because optical characteristics are frequently dependent on wavelength. Monochromators help scientists select a wavelength to determine the chemical makeup of various materials, and from there assist in examining more complex matters.

Single-crystal monochromators aid a monochromator application more common to the layperson: They help filter X-rays from their source beam and eliminate some of the radiation that could otherwise be dangerous, causing medical professionals to make an incorrect diagnoses. Elsewhere in industry and science, monochromators isolate light outside the visible spectrum, like ultraviolet (UV) and near-infrared (NIR), into a narrow band – essential to high-performance liquid chromatography.

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Exploring Optometrics Mini-Chrom Monochromators

Optometrics’ Mini-Chrom line of monochromators are made in the Fastie-Ebert configuration with a 74mm focal length and are compatible with UV, visible, and NIR spectrums. They differ from one another in the following ways:

  • The standard Mini-Chrom monochromator represents one of the most traditional mechanical forms of monochromators. Choose your desired wavelength by rotating the device’s micrometer to turn the precision sine bar drive as needed, and get to work!
  • As an alternative to that classic design, the digital Mini-Chrom monochromator is equipped with a digital wavelength selector, ideal for users who want to choose wave bands more quickly.
  • The scanning Mini-Chrom monochromator is designed for use with external servo-controlled or stepping motors.
  • The scanning digital Mini-Chrom monochromator is equipped with a digital counter and its own integral stepping motor. It displays the current wavelength at all times. When connected to the Optometrics PCM-02 calibrated drive via a 15-pin connector, users can control the motor to complete scans according to the requirements of their particular application.

Choosing the right monochromator

Choosing the right monochromator depends on the careful consideration of several factors. Here are some of the most important ones.

Intended application

All of the models detailed above are suitable for most academic, research, quality control, and engineering use that depends on spectroscopic analysis. These range from the examination of precursor chemicals for industrial compound creation to determining precise light settings in professional photography. But some applications may benefit more from one model versus another.

For example, situations in which a given scientific, academic, or engineering process requires scans of wavelength intervals (for either individual readings or continuous monitoring) will be better served by  scanning monochromators, due to the motor controls inherent in these models. The same is true for OEM system integration applications and tasks requiring the sequential selection of discrete wavelengths.

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Functional environment

Physical damage to monochromators or any tools connected to them may be possible, particularly in motor-driven models. The screw or pin mechanism used to tune to a specified wavelength can damage the internal mechanics if it is aggressively pushed beyond its wavelength limits. To mitigate this risk, Optometrics’ scanning monochromators are equipped with dual photosensors that serve as limit switches in both directions to prevent damage. While the standard and digital Mini-Chroms lack this feature, mechanical damage is unlikely due to the resistance users feel when manually controlling the wavelength selector.

Wavelength range

A monochromator will not do you any good if it cannot isolate light according to the wavelength specifications unique to your application. Imagine if your stage lights were not producing hues that were the precise colors of the light specified by an exacting director. What if the lighting in a controlled environment for an infrared application was not emitting the expected wavelength? Or perhaps your research is impacted because you are unable to accurately measure light reflectance with your optical system.

You do not have to worry about any of these scenarios when you choose the Mini-Chrom line. Each of the four models are available in bandwidth ranges spanning 190-650 nm at the shortest spectrum to 850-2200 nm at the longest, with six different spectrums in between.

Find the best monochromator for your application

With more than 30,000 monochromators sold, the Mini-Chrom line of monochromators is an affordable and reliable workhorse for a wide variety of industrial, academic, and scientific spectroscopic applications.

Need additional guidance? Contact us today to learn more or request a quote.

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