| Model 275D Double Monochromator modified Seya-Namioka design for Subtractive or Additive Operation
The Model 275D is a dedicated double grating monochromator providing additive or subtractive dispersion. The 275D compact housing contains the scanning mechanism and mechanical linkage of one precision wavelength sine drive for two gratings. Wavelength control is via the 789A-3 digital scan control with a single motor. The stepper drive (refer to Model 789A-3) is interfaced for operation via PC. |
Five scans over Hg 253.6-nm, repeats to < 0.1-nm |
Model 275D focal length is 0.2 meters and it can be configured for additive or subtractive dispersion. The optically and mechanically coupled modified Seya-Namioka systems are equipped with aberration corrected concave holographic gratings. Spectrally agile, the model 275D features all first surface optics for the best UV-Vis-NIR response. Double monochromators are used for a variety of applications that require extremely low levels of scattered or stray light. The most popular applications include:
- Additive Double Spectrometer delivers higher spectral resolution with low stray light commonly for Source / Detector Standardization
- Subtractive Double Spectrometer with symetrical spectral energy with low stray light commonly for Raman Spectroscopy and Photoluminescence
PDF format Data Sheet for the double mono Model 275D available here
Specifications
| Focal Length | (2X) 200 mm |
| Aperture Ratio | f/4.2 |
| Wavelength Range | 185 - 1000 nm |
| Resolution Divide by 2 for Additive mode specification. |
0.15-nm |
| Accuracy | ± 0.06 nm Vis (measured) ± 0.5 nm UV-Vis-IR |
| Repeatability | ± 0.05 nm UV-Vis-IR (measured) |
| Bandpass Divide by 2 for Additive mode specification. |
0.15 - 16 nm, varies with slit width |
| Stray Light (measured) | < 6.4 x 10-4 (UV NPL procedure) < 5.0 x 10-4 (UV-Vis NPL procedure) < 1.3 x 10-6, 10 nm from 632.8 nm (100 um slits) |
The Model 275D is reliably pretested with secondary monochromators and selected filters. It is a useful building block in customized test systems.
Low Stray Light Stray light is frequently characterized by laser sources. This approach yields impressive stray light data. Unfortunately, this is not pertinent for many applications. Using a laser source and measuring at 10-nm from a laser line indicates only scatter of its narrow band of spectral light. It does not address stray light produced by broad band or sources providing continuous light, i.e. Xe, XeHg, halogen or tungsten, etc. The 275D suppresses stray light produced by such sources. The 275D is a powerful analytical tool to select narrow stray light deprived pass bands. Source and detector characterization and many analytical procedures disturbed by stray light benefit by employing the 275D for more accurate profiling of background impaired investigative procedures.
| Wavelength | With GG395 Filter | Without GG395 Filter | Ratio (w/wo Filter) | % |
| 340 nm | 1.5 X 10-10 | 2.1 X 10-5 | 0.714 X 10-5 | 0.0007 |
| 350 nm | 1.6 X 10-10 | 1.7 X 10-5 | 0.941 X 10-5 | 0.0009 |
| Wavelength | With GG475 Filter | Without GG475 Filter | Ratio (w/wo Filter) | % |
| 400 nm | 1.6 X 10-10 | 3.5 X10 -5 | 0.457 X 10-5 | 0.0005 |
The United Kingdom standards organization, National Physics Laboratory (NPL) defined this procedure for specifying stray light when continuum sources are used. Scattered light is measured at a particular wavelength with and without a particular long pass filter in front of the slit.
Line Drawing for Model 275D Subtractive
