How to select optimal Optical Resolution?
 The optical resolution is defined as the minimum difference in wavelength that can be separated by the spectrometer. For separation of two spectral lines it is necessary to image them at least 2 array-pixels apart.
Because the grating determines how far different wavelengths are separated (dispersed) at the detector array, it is an important variable for the resolution. The other important parameter is the width of the light beam entering the spectrometer. This is basically the installed fixed entrance slit in the spectrometer, or the fiber core when no slit is installed.
The slits can be installed with following dimensions: 10, 25 or 50 x 1000 µm high or 100, 200 or 500 µm x 2000 µm high. Its image on the detector array for a given wavelength will cover a number of pixels. For two spectral lines to be separated, it is now necessary that they be dispersed over at least this image size plus one pixel. When large core fibers are used the resolution can be improved by a slit of smaller size than the fiber core. This effectively reduces the width of the entering light beam.
The influence of the chosen grating and the effective width of the light beam (fiber core or entrance slit) are shown in the tables at the product information.
In Table 3 the typical resolution can be found for the AvaSpec-2048. Please note that for the higher lines/mm gratings the pixel dispersion varies along the wavelength range and gets better towards the longer wavelengths (see also Figure 3).
The resolution in this table is defined as F(ull) W(idth) H(alf) M(aximum), which is defined as the width in nm of the peak at 50% of the maximum intensity (see Figure).
Graphs with information about the pixel dispersion can be found in the gratings section as well, so you can optimally determine the right grating and resolution for your specific application.
In combination with a DCL-detector collection lens or thick fibers the actual FWHM value can be 10-20% higher than the value in the table. For best resolution small fibers and no DCL is recommended.
Table 3 Resolution (FWHM in nm) for the AvaSpec-2048
*depends on the starting wavelength of the grating; the higher the wavelength, the bigger the dispersion and the higher the resolution
|
Slit size (µm)
|
|
Grating (lines/mm)
|
10
|
25
|
50
|
100
|
200
|
500
|
|
300
|
0.8
|
1.4
|
2.4
|
4.3
|
8.0
|
20.0
|
|
600
|
0.4
|
0.7
|
1.2
|
2.1
|
4.1
|
10.0
|
|
1200
|
0.1-0.2*
|
0.2-0.3*
|
0.4-0.6*
|
0.7-1.0*
|
1.4-2.0*
|
3.3-4.8*
|
|
1800
|
0.07-0.12*
|
0.12-0.21*
|
0.2-0.36*
|
0.4-0.7*
|
0.7-1.4*
|
1.7-3.3*
|
|
2400
|
0.05-0.09*
|
0.08-0.15*
|
0.14-0.25*
|
0.3-0.5*
|
0.5-0.9*
|
1.2-2.2*
|
|
3600
|
0.04-0.06*
|
0.07-0.10*
|
0.11-0.16*
|
0.2-0.3*
|
0.4-0.6*
|
0.9-1.4*
|
| 
CORPORATE