How to Choose the Right Miniature Spectrometer

Choosing the right miniature spectrometer is very application-dependent, so there are a few questions that need to be asked. What are you trying to measure and why? How fast do you need measurements? Where is the

sample and who will be operating the instrument? The design also involves money, so it is important to have a cost target for the system in mind as well.

To configure a spectrometer, there are some important choices that need to be made, such as the choice of wavelength range, optical resolution and system sensitivity. The optical bench directs broadband (white) light through a narrow entrance slit onto a diffraction grating and focuses the spectrum onto a detector array. The wavelength range will depend on the groove density of the grating and the details of the bench and detector.

The wavelength range is determined by the grating. With each grating, you consider its groove density (which helps determine the resolution), its spectral range (which helps determine the wavelength range) and its blaze

wavelength (which helps determine the most efficient range). Instead of the gratings rotating as they do in instruments such as scanning monochromators, the gratings in most miniature spectrometers are fixed in place to ensure long-term performance and stability. A grating must be specified for each spectrometer.

The groove density (mm-1) of a grating determines its dispersion, while the angle of the groove determines the most efficient region of the spectrum. The rule of thumb is this: The greater the groove density, the better the

optical resolution possible, but the smaller the spectral range. The spectral range is the dispersion of the grating across the linear array. The spectral range (bandwidth) is a function of the groove density and does not change.