What is a Spectrometer?


Courtesy of Larson Electronics LLC

The characteristics of a white LED light differs greatly, when compared to a yellow CFL. Without any special tools, one can see that the LED emits a clear white color, while the CFL generates yellow light. Going one step further, using a spectrometer, one will be able to “dissect” the light sources and see that they are composed of other colors in the visible light spectrum, such as blue bands in LEDs.

Spectrometer Mechanisms

Spectrometers are instruments used to measure properties of light in relation to its function in (but not limited to) the electromagnetic spectrum. The fundamentals of the practice, called spectroscopy, involves deep analysis of specific light bands by breaking down the light source. For example, basic light analysis tools may break up light into red, blue and green colors, possibly using a prismatic feature. Spectroscopy could take the same light and break it down into specific wavelengths and bands, represented by their respective numerical associations.

During testing, the light source is projected towards the spectrometer. As it goes through the entrance slit, the beam is reflected off a collimating mirror and goes through a diffraction grating, where it is split up into different components (i.e., colors, wavelengths or energies). The end result is a dissected image of the light source with specific wavelengths of light either dominantly present or completely missing. Researchers may take a photo of the image for further analysis.

It is important to consider that this practice does not take all light from an object into account. Instead, it focuses on very specific wavelengths or colors. When analyzing specific sources of light, such as fluorescents, metal halide lamps and LEDs, a spectrometer can be used to probe for various components in the beam. For instance, black lights, which emit UVA bands between 315 nm and 400 nm, display mostly violet and some blue wavelengths when viewed through a spectrometer. This makes sense because violet bands fall between 380 nm and 450 nm (within the UVA spectrum range), while blue wavelengths generate bands around 450 nm and 495 nm.

Spectrometer-related Devices

In spectroscopy, there are a handful of devices with similar features but ultimately do different things. As defined earlier, spectrometers specifically measure the source’s emission. It can establish which bands are absorbed or reflected. A spectroscope is a tool that is designed to measure the spectrum of a light source. While a spectrograph is a device that filters an incoming light source by its respective wavelength or frequency. It takes the results and records the signal using a camera or a multichannel detector.

In the field of spectrophotometry, the light source is broken down into different wavelengths via diffraction grating. The diffracting component is manipulated, so that only specific bands pass through the exit slit. The diffused portion of the light exiting the slit then interacts with a sample, where a detector measures the absorbance, reflection and transmittance of the interaction.

Types of Spectroscopy and Applications

Spectrometers can be found in numerous industries, ranging from molecular biology and analytical chemistry to industrial manufacturing and space exploration. Although it is common practice to use the device on visible light, scientists may also use high-powered spectrometers to observe non-visible wavelengths, such as infrared.

Below expounds on specific types of spectroscopy practices and its applications in various technical fields:

  • Absorption Spectroscopy: This practice involves the use of spectroscopic methods to measure and analyze the absorption of radiation based on light interaction with a sample. The technique is applicable to atomic absorption spectroscopy (AAS), during close analysis of chemical elements- also known as analytical chemistry.
  • Infrared Spectroscopy: Infrared spectroscopy deals with exposing samples to infrared wavelengths in the electromagnetic spectrum, as well as the real-time measurement of “vibrations of inter atomic bonds at different frequencies.” This spectroscopic method incorporates foundational practices in the field of absorption spectroscopy; hence it is also typically used in analytical chemistry. Furthermore, it can be used to support forensic analysis during criminal cases (e.g., analyzing alcohol content in a blood sample).
  • Ultraviolet (UV) Spectroscopy: This spectroscopy method works by exposing a sample to UV and near-UV wavelengths using a UV light source. Scientists measure the absorbance rate of the sample based on the level of excitement that electrons display during application. UV spectroscopy is mostly used to monitor molecular chemical bonding.
  • Laser Spectroscopy: Based on the examples above, spectrometers are capable of incorporating different light sources during testing. Laser spectroscopy takes this general practice one step further by using lasers as a radiation source. Common laser light sources include fiber lasers, dye lasers and titanium-sapphire lasers that are capable of emitting infrared and near-infrared bands between 700 nm and 1,100 nm.

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