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

Choosing a Grating & Wavelength Range:
"HR" Optical Bench

You choose from among 14 gratings for each spectrometer. With each grating, you consider its groove density (which helps determine the resolution), its spectral range (which helps determine the wavelength range) and its blaze wavelength (which helps determine the most efficient range). Instead of the gratings rotating as they do in instruments such as scanning monochromators, our gratings are permanently fixed in place at the time of manufacture to ensure long-term performance and stability. A grating must be specified for each spectrometer. We offer ruled and holographic diffraction gratings. Both are polymer replicas of master gratings. There are trade-offs between these gratings: holographic gratings produce less stray light while ruled gratings are more reflective, resulting in higher sensitivity.

Grating Selection Chart

The chart below allows you -- with the help of our Applications Scientists -- to select the best grating. Bulleted items describe each column in the table.

Groove Density. The Groove Density (mm^-1) of a grating determines its dispersion, while the angle of the groove determines the most efficient region of the spectrum. The greater the groove density, the better the optical resolution possible, but the more truncated the spectral range.
Spectral Range. The dispersion of the grating across the linear array; also expressed as the "size" of the spectra on the array. The spectral range (bandwidth) is a function of the groove density and does not change. When you choose a starting wavelength for a spectrometer, you add its spectral range to the starting wavelength to determine the wavelength range. The Spectral Range of a grating varies according to the starting wavelength range. The rule of thumb is this: The higher the starting wavelength, the more truncated the spectral range.
Blaze Wavelength. For ruled gratings, the Blaze Wavelength is the peak wavelength in an efficiency curve. For holographic gratings, it is the most efficient wavelength region.
Best Efficiency ( >30%). All ruled or holographically etched gratings optimize first-order spectra at certain wavelength regions; the "best" or "most efficient" region is the range where efficiency is >30%. In some cases, gratings have a greater spectral range than is efficiently diffracted. For example, Grating H1 has about a 430 nm spectral range, but is most efficient from 200-575 nm. In this case, wavelengths >575 nm will have lower intensity due to the the grating’s reduced efficiency.

Grating Number	Intended Use	Groove Density	Spectral Range	Blaze Wavelength	Best Efficiency (>30%)
HC-1	UV-NIR	300	200-1100 nm	variable	200-1100 nm
H1	UV	600	425-445 nm	300 nm	200-575 nm
H2	UV-VIS	600	415-445 nm	400 nm	250-800 nm
H3	VIS-Color	600	410-440 nm	500 nm	350-850 nm
H4	NIR	600	410-430 nm	750 nm	530-1100 nm
H5	UV-VIS	1200	205-220 nm	Holographic UV	200-400 nm
H6	NIR	1200	140-195 nm	750 nm	500-1100 nm
H7	UV-VIS	2400	72-102 nm	Holographic UV	200-500 nm
H9	VIS-NIR	1200	165-205 nm	Holographic VIS	400-800 nm
H10	UV-VIS	1800	95-140 nm	Holographic UV	200-635 nm
H11	UV-VIS	1800	75-135 nm	Holographic VIS	320-720 nm
H12	UV-VIS	2400	60-100 nm	Holographic VIS	260-780 nm
H13	UV-NIR	300	800-900 nm	500 nm	300-1100 nm
H14	NIR	600	410-420 nm	1000 nm	650-1100 nm

Grating Efficiency Curves

To see the efficiency curve of a specific grating, and to compare similar gratings, click on the Grating Number in the far left column of the table or click here.

Predicted Ranges & Resolutions

See a series of graphs to demonstrate the predicted Range and Resolution of your HR4000 Spectrometer, which depend on the grating, slit and starting wavelength choices selected.

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Choosing a Grating & Wavelength Range: "HR" Optical Bench

Grating Selection Chart

Choosing a Grating & Wavelength Range:
"HR" Optical Bench