The diffraction grating is an optical component which can decompose the incident polychromatic light into monochromatic light it contains. Grating is constituted by series parallel grooves of the same width and spacing, and these grooves are carved and made on the substrate material plated with reflective film. The grating can be divided into two kinds by the different formations of grooves, they are: Holographic grating and Ruled grating. Ruled grating is carved mechanically by the diamond graver on the reflection surface of coated thin metal; while the holographic grating is formed by laser beam interference pattern and lithography process. There are both the holographic grating and a ruled grating in the United States ocean optics spectrometer. The grating in fiber optic spectrometer has to be specified by the use, and be permanently installed in the spectrometer. Next the user will have to indicate the wavelength range needed. Sometimes the grating nominal can take advantage of the spectral range which is greater than the spectral range exposed on the detector, at this time in order to cover a wider spectral range, we can choose the spectrometer with dual or three channels. Different gratings can be selected from these main channels and secondary channels.Similarly, dual or three- channel spectrometer can also enable users to achieve higher resolution in a wide spectral range. In the introduction of spectrometer, there is a grating selection table for each spectrometer. It describes how to understand these gratings selection tables.
The spectral range depends on the starting wavelength and raster line logarithms.
The longer the wavelength is, the bigger the dispersion effect will be, and the wavelength range covered by the grating is smaller. The efficiency of the spectrometer is determined by the transmission efficiency of optical fiber, the efficiency of grating and reflector, detectors and film sensitivity.
Note: it depends on the starting wavelength of grating; the longer the wavelength is, the greater the grating dispersion will be, and the smaller the actual spectral range becomes.
The selection for other types of grating and wavelength range tables, you can refer to www.lisungroup.com