Spectrometers

Light passes through the installed slit, which acts as the entrance aperture. Slits come in various widths from 5 µm to 200 µm. The slit is fixed in the SMA 905 bulkhead to sit against the end of a fiber. Smaller slit sizes achieve the best optical resolution while larger slits have higher light throughput. The slit size of our Flame spectrometer is labeled as shown.

Ocean Optics also offers a range of FC connector slits in the same slit widths, with the product code INTFC-XXX. An INTFC-KIT is also available. Note that these items are made to order and have a longer lead time.

SAG+ mirrors are often specified for fluorescence. These mirrors absorb nearly all UV light, which reduces the effects of excitation scattering in fluorescence measurements. Unlike typical silver-coated mirrors, the SAG+ mirrors won’t oxidize. They have excellent reflectivity — more than 95% across the VIS-NIR.

Flame and USB Series Custom Configured Gratings and Wavelength Range

Gratings for Ocean Optics spectrometers are permanently fixed in place at the time of manufacture to ensure long-term performance and stability. Choose from among multiple gratings for your custom configured Flame spectrometer. When selecting your grating, consider groove density (resolution), spectral range (wavelength range) and blaze wavelength (determines the most efficient range). We offer ruled and holographic diffraction gratings. Holographic gratings produce less stray light while ruled gratings are more reflective, resulting in higher sensitivity.

* Spectral range will be smaller when starting wavelength is longer. Spectral range also depends on exact spectrometer model.

** For applications >720 nm, please consult an Application Sales Engineer.

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. For several gratings, the Spectral Range of a grating varies according to the starting wavelength range. The rule of thumb is: 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 1 has about a 650 nm spectral range, but is most efficient from 200-575 nm. In this case, wavelengths >575 nm will have lower intensity due to the grating’s reduced efficiency.

This mirror focuses first-order spectra on the detector plane. Both the collimating and focusing mirrors are made in-house to guarantee the highest reflectance and the lowest stray light possible. You can opt to install a standard Al or special coated Ag (SAG+) mirror. As with the collimating mirror, the mirror type needs to be specified when ordering.

There are two choices of detector available for the Flame spectrometer. We offer a 2048-element FLAME-S (Sony ILX511B) or a 3648 element FLAME-T (Toshiba TCD1304AP) linear CCD array. These both have an effective range of 190-1100 nm. The optics split the light into its component wavelengths which fall across the different pixels. Each pixel responds to the wavelength of light that strikes it. The detector outputs an analog signal from each pixel that is converted via the ADC into a digital signal. The driver electronics process this signal and send the spectrum via the USB connection to the software. The best choice of detector will depend on the application.

Detector specifications sheets:

Toshiba-TCD1304AP-CCD-array
SONY-ILX511B

Our proprietary filters precisely block second- and third-order light from reaching specific detector elements. Light reflected off the grating can propagate 2nd and 3rd order effects at whole multiples of the incident light wavelength. So, for example, 250nm light hits the first order position at 250nm, and the second order position at 500nm. While 2nd order is generally weaker than first order signals, they are troublesome when looking at broad band spectra. Order sorting filters reject this stray light only allowing the desired 1st order wavelength through to the detector.

Order sorting filters are installed on detectors and are listed in the detector selection pane below. They are only available at set wavelength ranges, as the filters have to be fabricated to align all the proper blocking bands to specific ranges on the detectors. These must be specified at the time of ordering.