USER CONFIGURED / SPEC RES+ UC
For the best resolution and affordable price in a user configured spectrometer we recommend the SPEC RES+ UC platform. The Toshiba detector with 3648 elements used in the this system can be combined with narrow slits for optical resolutions better that 0.1nm. With peak wavelength at 550nm this system offers great sensitivity in the visible range.
The detector platform includes the detector, electronics and mirrors. The configuration is only complete with a slit, grating, filters (if required) and collecting lens (if required).
Sarspec’s SPEC spectrometers use a symmetrical Czerny-Turner optical configuration. In a simple way, the Czerny-Turner optical bench has the following components: entrance slit (2), collimating mirror (4), grating (5), focusing mirror (6) and detector (9). The light from a source enter through the slit which is placed in the focus of a collimating mirror that collimates the light to the diffraction grating which “separates” the light into different wavelengths. The light diffracted from the grating reach a second mirror, the focusing mirror, which will focus the spectrum into the detector. The representation at the end of this page illustrates several components of this configuration.
In a traditional spectrophotometer, the detector has only a single element and the wavelength detected changes with the rotation of the grating (moving part) allowing scanning the desired spectral range. In Sarspec’s SPEC series spectrometers the grating is fixed and instead of single element Sarspec uses linear array elements (pixels), each pixel from the detector works as an individual detector, with an individual signal, allowing the acquisition of a full spectrum in real time and making a more robust instrument because there’s no mechanical ware due to grating rotation.
To optimize the final solution with respect to range, sensitivity and stray light, Sarspec introduced some improvements to the standard Czerny-Turner configuration. As a result there are Longpass Filters (3), order sorting Filters (7) and Collecting Lens (8) available to add and optimize each configuration to meet user’s requirements. All instruments from Sarspec use SMA 905 connectors (1) for easy optical fiber coupling, without the need of any alignment.
Important concepts when configuring a spectrometer:
1. Wavelength range - For a given focal distance (f) and detector size, the wavelength range is determined by the grating dispersion, for wider ranges it’s necessary to choose gratings with low groove density (lines/mm). The lowest groove density available from Sarspec is 500 lines/ mm which corresponds to a spectral range around 850 nm and the highest is 2400 lines/mm for 175 nm spectral range. We recommend order sorting filter or longpass filters to avoid higher orders of diffraction in the detector.
2. Optical Resolution - There are three components that influence the resolution of the spectrometer: slit, grating and detector. As we increase the number of lines/ mm in the grating we get shorter spectral range but better resolution. The slit width controls the “image size” on the detector and the smaller the slit width better the resolution. The number of pixels also affects the resolution, more pixels better resolution, but that is only true when the ratio between pixel and slit size are close to 1.
3. Sensitivity - Sensitivity is determined mainly by the slit size and detector. Wider the slit, more light is the detector receiving resulting in better sensitivity. With the detectors, the sensitivity increases with the quantum efficiency and pixel area. The use of collecting lens can improve the signal up to 6 times and we strongly advise them when performing low light level measurements.
4. Speed - Speed depends on the detector and electronics. It’s important to understand that integration time (the time that the detector is exposed to light) is different of acquisition time (the time to acquire, transfer and save the spectra). Sarspec clearly identifies both in every configuration. All spectrometers available from Sarspec allow great acquisition speed but for ultimate performance we recommend the platform SPEC SPEED+.
First optical element, limits the amount of light entering the spectrometer. Rectangular geometry, with standard 1 mm height and variable width from 10 µm to 200 µm (pre-selected and factory installed). The slit width is crucial in the determination of the spectrometer resolution and sensitivity. The table below shows the resolutions obtained with the 2048 pixels detector from the SPEC STD spectrometer with the different slits available from Sarspec.
|Resolution for available slits when using the SPEC RES+ UC platform (nm)|
|Grating||Slit 10 µm||Slit 25 µm||Slit 50 µm||Slit 100 µm||Slit 150 µm||Slit 200 µm|
|3600||0.2 / 0.1||0.2 / 0.2||0.4 / 0.3||0.5 / 0.5||0.7 / 0.7||0.9 / 0.9|
The dispersive element that “separates” the light into its spectral components allowing that at each pixel of the detector receives a specific wavelength range. The grating is fixed and it's crucial for the resolution, wavelength range and sensitivity of the spectrometer. All gratings have a specific performance which can be found in the efficiency curves in the link below. An efficiency higher than 25% should be considered when choosing the wavelength range.
|Part Number||Description||Useable range (nm)||Spectral Range (nm)||Best efficiency >25%|
|G500-300||Grating 500 lines/mm, blazed @300 nm||200 - 1100||850||250 - 750|
|G600-300||Grating 600 lines/mm, blazed @300 nm||200 - 1100||700||200 - 650|
|G600-500||Grating 600 lines/mm, blazed @500 nm||250 - 1100||700||300 - 1100|
|G600-750||Grating 600 lines/mm, blazed @750 nm||400 - 1100||670||400 - 1100|
|G1200-250||Grating 1200 lines/mm, blazed @250 nm||200 - 1100||320*||200 - 750|
|G1200-500||Grating 1200 lines/mm, blazed @500 nm||250 - 1100||280||300 - 1100|
|G1200-750||Grating 1200 lines/mm, blazed @750 nm||450 - 1100||250*||475 - 1100|
|G1800-250||Grating 1800 lines/mm, blazed @250 nm||200 - 800||220||200 - 450|
|G1800-500||Grating 1800 lines/mm, blazed @500 nm||200 - 1050||200*||320 - 1000|
|G2400-UV||Grating 2400 lines/mm, UV||200 - 800||150*||200 - 420|
|G2400-Vis||Grating 2400 lines/mm, Vis||220 - 820||100*||250 - 800|
|G3600-UV||Grating 3600 lines/mm, UV||200 - 500||80*||250 - 500|
Longpass filter is placed after the slit to reject shorter wavelength in the range of interest. Usefull to avoid higher orders of diffraction to read the detector and reduce the stray light radiation to get to the detector.
|SLPF-280||Longpass filter λc = 280 nm (@ T=50%)|
|SLPF-320||Longpass filter λc = 320 nm (@ T=50%)|
|SLPF-395||Longpass filter λc = 395 nm (@ T=50%)|
|SLPF-515||Longpass filter λc = 515 nm (@ T=50%)|
|SLPF-630||Longpass filter λc = 630 nm (@ T=50%)|
Order Sorting Filters
Order Sorting Filters prevents higher orders of diffraction to reach the detector. Sarspec has a wide range of solutions and selects the best option for each configuration.
|OSF-CUSTOM||Order Sorting Filters - customized solution|
The collecting lens are cylindrical lens placed on front of the detector for focusing the entire height of the beam into the height of the pixels. The special design from Sarspec results in a increase in the sensitivity up to 6 times, depending on the optical fiber and detector used.
|CL-CUSTOM||Collecting Lens - customized solution|
|Wavelength range||180 - 1100 nm|
|Detector||3648 pixels CCD array Toshiba|
|Pixel width x height||8 x 200 µm|
|Optical design||Symmetrical Czerny-Turner|
|Focal length||50 mm|
|Dark noise (RMS)||32|
|Integration time||3 ms - 214 s|
|QE (%) @ peak||40%|
|Peak wavelength||550 nm|
|Pixel well depth||120000|
|A/D Converter||16 bits|
|Interface||Mini USB 2.0|
|Fiber connector||SMA 905|
|Dimensions||116 (L) x 93 (D) x 55 (H)|