Optical resolution, measured as Full Width Half Maximum (FWHM), of a monochromatic source depends on the groove density (lines/mm) of the grating and the diameter of the entrance optics (optical fiber or slit). In configuring your spectrometer, consider two important trade-offs: 1) Resolution increases with an increase in the groove density of the grating, but at the expense of spectral range and signal strength; and 2) Resolution increases as the slit width or fiber diameter decreases, but at the expense of signal strength.

The approximate optical resolution in nm (FWHM) can be calculated as follows:

1) Dispersion (nm/pixel) = Spectral Range of the Grating (see information on choosing gratings) ÷ Number of Detector Elements (2048 for S2000 series or 1024 for S1024DW)

2) Resolution (in pixels) = value from slit size/fiber diameter chart (see below)

Typical pixel resolution by slit size/fiber diameter:

5 micron slit =	~3.0 pixels
10 micron slit =	3.2 pixels
25 micron slit =	4.2 pixels
50 micron slit =	6.5 pixels
100 micron slit =	12.0 pixels
200 micron slit =	24.0 pixels

3) Optical Resolution (in nm) = Dispersion (nm/pixel value from #1) x Resolution (pixels value from #2)

EXAMPLE: S2000 Spectrometer with Grating #3, 10-micron slit

    650 nm ÷ 2048 = 0.32 nm/pixel x 3.2 pixels = 1.02 nm (FWHM)

Contact an Ocean Optics Applications Scientist

Choosing Gratings 

System Sensitivity

Operating Principles