A diffraction grating is an optical element that separates incident polychromatic radiation into its constituent wavelengths. A grating consists of series of equally spaced parallel grooves formed in a reflective coating deposited on a suitable substrate.

gratings.jpg

The way in which the grooves are formed separates gratings in two types, holo-graphic and ruled. The ruled gratings are physically formed onto 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.

Avantes AvaSpec spectrometers come with a permanently installed grating that must be specified by the user. Additionally 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 multi-channel spectrometer can be chosen. In this configuration each channel may have different gratings covering a segment of the range of interest. In addition to broader range, a dual or multi-channel spectrometer also affords higher resolution for each channel.

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.

Below the grating 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 quantum efficiency and coating sensitivities. The all new dual-blazed grating is a 300 lines/mm broadband grating (covering 200-1100 nm) that has optimized efficiency in both UV and NIR. On the bottom the grating dispersion curves are shown for the AvaSpec-ULS2048.

 

grating selection

Grating Efficiency Curves
300 lines/mm gratings
Grating 300
600 lines/mm gratings
Grating 600
1200 lines/mm gratings
Grating 1200
1800 lines/mm gratings
Grating 1800
2400 lines/mm gratings
Grating 2400
3600 lines/mm gratings
Gratings-Overview pag12
HS 500 lines/mm gratings
HS500
HS 830-1000 lines/mm gratings
HS830-1000
HS 1200 lines/mm gratings
HS 1200
NIR 100-200 lines/mm gratings
NIR 100-200
NIR 200-300 lines/mm gratings
NIR 200-300
NIR 300-400 lines/mm gratings
Grating overview NIR pag 13

 

Grating Dispersion Curves
300 lines/mm gratings
Avabench75 2048-pag14
600 lines/mm gratings
disp 600
1200 lines/mm gratings
disp 1200
1800 lines/mm gratings
disp 1800
2400 lines/mm gratings
disp 2400
3600 lines/mm gratings
disp 3600