The ruled gratings are physically formed into a reflective surface with a diamond on a ruling machine. Gratings produced from laser constructed interference patterns and a photolithographic process are known as holographic gratings.
The fiber optic spectrometer comes with a permanently installed grating that must be specified by the user. Further the user needs to indicate what wavelength range needs to reach the detector. Sometimes the specified usable range of a grating is larger than the range that can be projected on the detector. In order to cover a broader range, a dual or triple beam spectrometer can be chosen. Then master and slave(s) have different gratings. Similarly, a higher resolution over a wide range can be achieved by using a dual or triple spectrometer.
For each spectrometer type a grating selection table is shown in the spectrometer platform section.
Table 2 illustrates how to read the grating selection table. The spectral range to select in Table 2 depends on the starting wavelength of the grating and the number of lines/mm; the higher the wavelength, the bigger the dispersion and the smaller the range to select.
In the figures below their efficiency curves are shown.
When looking at the grating efficiency curves, please realize that the total system efficiency will be a combination of fiber transmission, grating and mirror efficiency, detector and coatings sensitivities.
In the figures below the grating dispersion curves are shown for the AvaSpec-2048.