Ocean Optics - Inventor of the World's First Miniature Spectrometer
Ocean Optics - Inventor of the World's First Miniature Spectrometer
 

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Ocean Optics - Inventor of the World's First Miniature Spectrometer

Optical Resolution 

Optical resolution of a monochromatic source -- -- measured as Full Width Half Maximum (FWHM) -- depends on the groove density (mm-1) 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.

How to Calculate the Approximate Optical Resolution in nm (FWHM)

1. Determine the Spectral Range of the Grating. You can find the Spectral Range of Gratings at:

2. Divide the Spectral Range of the Grating by the Number of Detector Elements. The resulting value is the Dispersion.

Dispersion (nm/pixel) = Spectral Range of the Grating/Number of Detector Elements

The table below lists the Detector Elements for various spectrometer benches and models.

Spectrometer

Number of Detector Elements

Jaz Spectrometer 2048
USB2000 Spectrometer

2048

USB2000+ Spectrometer 2048
USB4000 Spectrometer

3648

HR2000 Spectrometer

2048

HR4000 Spectrometer

3648

NIR256-2.1 Spectrometer

256

NIR256-2.5 Spectrometer

256

NIR512 Spectrometer

512

NIR512-2.2 Spectrometer

512

QE65000 Spectrometer

1044

3. Determine the Pixel Resolution

The pixel resolution is listed below for various sizes of slits (or the optical fiber diameter if the fiber is the limiting factor). The width of the entrance aperture slits differs; the Height of all slits are the same (1000 microns).

Spectrometer 5 micron
Slit
10 micron
Slit
25 micron
Slit
50 micron
Slit
100 micron
Slit
200 micron
Slit
Jaz Spectrometer ~3.0 pixels ~3.2 pixels ~4.2 pixels ~6.5 pixels ~12.0 pixels ~24.0 pixels
USB2000 Spectrometer ~3.0 pixels ~3.2 pixels ~4.2 pixels ~6.5 pixels ~12.0 pixels ~24.0 pixels
USB2000+ Spectrometer ~3.0 pixels ~3.2 pixels ~4.2 pixels ~6.5 pixels ~12.0 pixels ~24.0 pixels
USB4000 Spectrometer ~5.3 pixels ~5.7 pixels ~7.5 pixels ~11.6 pixels ~21.0 pixels ~42.0 pixels
HR2000 Spectrometer ~1.5 pixels ~2.0 pixels ~2.5 pixels ~4.2 pixels ~8.0 pixels ~15.3 pixels
HR2000+ Spectrometer ~1.5 pixels ~2.0 pixels ~2.5 pixels ~4.2 pixels ~8.0 pixels ~15.3 pixels
HR4000 Spectrometer ~2.0 pixels ~3.7 pixels ~4.4 pixels ~7.4 pixels ~14.0 pixels ~26.8 pixels
NIRQuest
512 Optical Resolution
N/A ~1.3 pixels ~2.0 pixels ~2.3 pixels ~4.2 pixels ~7.9 pixels
NIRQuest
512-2.2 Optical Resolution
N/A ~1.3 pixels ~2.0 pixels ~2.3 pixels ~4.2 pixels ~7.9 pixels
NIRQuest
512-XR Optical Resolution
N/A 1.3 pixels 2.0 pixels 2.3 pixels 4.2 pixels 7.9 pixels
NIRQuest
512-1.9 Optical Resolution
N/A 1.3 pixels 2.0 pixels 2.3 pixels 4.2 pixels 7.9 pixels
NIRQuest
256-2.1 Optical Resolution
N/A ~1.5 pixels ~1.7 pixels ~2.0 pixels ~2.5 pixels ~4.0 pixels
NIRQuest
256-2.5 Optical Resolution
N/A ~1.5 pixels ~1.7 pixels ~2.0 pixels ~2.5 pixels ~4.0 pixels
QE65000 Spectrometer ~2.0 pixels ~2.2 pixels ~2.6 pixels ~3.3 pixels ~4.7 pixels ~8.9 pixels

4. Calculate the Optical Resolution (in nm)

Dispersion (Step 2) x Pixel Resolution (Step 3)

Example: Determine the Optical Resolution of a USB4000 Spectrometer with Grating #3, 10-micron Slit

650 nm (spectral range of Grating #3)/3648 (detector elements in USB4000) = 0.18 nm/pixel x 5.7 pixels = 1.0 nm (FWHM)

Note: Values rounded up to nearest tenth.

Contact an Ocean Optics Applications Scientist

System Sensitivity

Operating Principles

 
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