The Basic Working Principle of a Spectrometer

Over the past two decades, miniature fiber optic spectrometers have evolved from a novelty to the spectrometer of choice for many modern spectroscopists. People are starting to realize the advanced flexibility and utility offered by their compatibility with a range of sampling accessories and their small size.

Basic Function of Spectrometers

The basic function of any spectrometer is to take in light, break it into its spectral components, digitize the signal as a function of wavelength, and read it out and display it via a computer. In the first step of this process, light is directed through a fiber optic cable into the spectrometer through an entrance slit, which is a narrow aperture.

The slit vignettes the light as it enters the spectrometer. Then, in most spectrometers, the divergent light is collimated by a concave mirror and directed onto a grating. Following this, the grating disperses the spectral components of the light at slightly varying angles.

The light is then focused by a second concave mirror and imaged onto the detector. Alternatively, all of the three functions can be simultaneously performed using a concave holographic grating. There are various pros and cons to this alternative, which are discussed in the article titled,“An Introduction to a Spectrometer: Diffraction Grating”

Once the light is imaged onto the detector, the photons are converted into electrons. These electrons are digitized and read out through a USB (or serial port) to a computer.

Based on the number of pixels in the detector and the linear dispersion of the diffraction grating, the software interpolates the signal to generate a calibration that enables the data to be plotted as a function of wavelength over the given spectral range. This data can be subsequently used and manipulated for many spectroscopic applications.

The following sections explain the inner-workings of a spectrometer and how all of the components work together to obtain a desired outcome. Each component is discussed in detail to provide a better insight into their function in the workings of a spectrometer.

This information has been sourced, reviewed and adapted from materials provided by B&W Tek.

For more information on this source, please visit B&W Tek.

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