A spectrometer’s performance is characterized by three central features. Wavelength range Resolution Sensitivity No spectrometer can maximize all three parameters at the same time, because these parameters have reciprocal relationships among one another. The art of spectrometer construction is to develop a balanced configuration which is optimally suited to the particular needs of the customer. As a result, a wide variety of massproduced configurations target individual customer requirements.

The following static parameters in the spectrometer determine the configuration:

• The groove density in the grating
•  The blaze wavelength of the grating
• The width of the slit
• The number of pixels in the detector
• The focal length of the lens
• The numerical aperture

While the focal length and numerical aperture are fixed according to the construction of the optical cell, the other static parameters can be adjusted individually in customizing the spectrometer.

Wavelength Range

A Spectrometer can work either with a particularly high resolution in a small wavelength range (like a telephoto lens) or in a wide range with a correspondingly reduced resolution (like a wide-angle) lens. Essentially the grating is responsible for these settings. A high groove density produces a small wavelength range with a high resolution. The detector array must be able to represent this range suitably.

Resolution

The optical resolution is defined by the bandwidth (Δλ_FWHM) with which monochromatic light is detected. A high resolution is achieved by using a high groove density in the grating (see above). The resolution can also be raised by using a small slit width. The sensitivity of the spectrometer decreases as the slit becomes smaller. The pixel resolution is determined by the number of pixels in the line detector. The resolution must be at least twice as high, otherwise the optical resolution cannot be represented.

Sensitivity

The sensitivity depends on the amount of light which enters the device. The wider the entry slit, the higher the sensitivity. At the same time, a small slit is required for high resolution. The blaze wavelength of the grating should be optimized to the wavelength range for maximum sensitivity.