The optical resolution of spectrometer is the smallest wavelength difference that the spectrometer can distinguish. To separate the two spectral lines, you have to make them image onto the two adjacent pixels on the detector at least. Because the grating determines the degree that different wavelength can be separated on the detectors (dispersion), therefore it is an important parameter for deciding spectrometer resolution.
Another important parameter is the light beam width that enters into the spectrometer, It basically depends on the entrance slit of fixed width installed on the spectrometer or fiber core diameter(when the slit is not installed).The sizes that Lisun Group provides are : 5，10，25，50，100，200μm×1000μm(high). At the specified wavelength, the slit’s images on the detector array usually can cover several pixels. If you want to separate the two spectral lines, you must put their dispersion image size coupled with another pixel. When using a large core diameter optical fiber, the resolution rate of spectrometer can be improved by choosing the slit which is narrower than the fiber core diameter, as this will reduce the width of the incident light beam greatly.
There is an introduction for the resolution effect table on the effective width of the selected grating and incident light beam (optical fiber core diameter or the entrance slit), table one is the typical resolution table for LMS-1000 spectrometer. Please note, the higher the line logarithm of grating is, the more remarkable the change of dispersion effect along wavelength will be, the longer the wavelength is, the greater the dispersion effect will be (shown in table one), the highest resolution will be achieved at the longest wavelength. There is also a pixel dispersion map in the chapter of grating, you can use it to choose the proper grating and resolution for the specified application.
NOTE: the above resolution is general. Specifically, it depends on the starting wavelength of the grating; the longer the wavelength is, the greater the grating dispersion will be, and the higher the resolution will be.
The effect of resolution from effective width of the selected grating and incident light beam(optical fiber core diameter, or the entrance slit), is shown as below, Table 1 shows the typical resolution values of the LMS-1000 fiber optic spectrometer. Please note, the higher the line logarithm of grating is, the more remarkable the change of dispersion effect along wavelength will be, the longer the wavelength is, the greater the dispersion effect will be, the highest resolution will be achieved at the longest wavelength. The definition of resolution in Table 1 is the spectral line width (nm) at the maximum peak intensity of 50% (FWHM).
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