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Model 218 Vacuum Monochromator Criss Cross Czerny Turner Optical Design
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The McPherson Model 218 is a proven performer in the Vacuum Ultraviolet (UV). Used under vacuum or with inert purge gases, it is also useful in Infrared applications where water bands, etc. may be eliminated. There are thousands of these monochromators working in laboratories all around the world. The optical system is very compact due to the unique criss cross optical design. Patented by McPherson, this approach allows shallow angles of incidence and diffraction. Users benefit by improved line shape and resolution. The large 44-degree angle between entrance and exit slits provides ample work space.
Grating scans are accomplished via the Model 789A-3 digital scan controller and/or related software. Existing instrument using synchronous drive systems may be upgraded to stepper control. An upgrade kit is available to facilitate the changeover, and bring the older 218s up to date wavelength control.
The Model 218 is built for use as a scanning monochromator and it may be retrofit with CCD detectors. There are some restriction on focal plane width and mounting so please contact us to discuss the options. Note that due to the Model 218s popularity and continued use in the field there are many gratings, stepper motor and detector upgrades available. We also provide rebuild or refurbishment services for instruments being returned to service after storage.
Click here for the Model 218 PDF format Data Sheet
Specifications
| Focal Length | 300-mm, criss cross Czerny Turner design |
| Angle between Entrance and Exit Beams | 44-degrees |
| f / No. | 5.3 |
| Grating Size | 50 x 50-mm |
| Wavelength Accuracy | +/-0.10 nm (on mechnical counter with 1200 G/mm grating) |
| Wavelength Reproducibility | +/- 0.005 nm (with 1200 G/mm grating) |
| Focal Plane | 17-mm maximum width |
| Wavelength Range | refer to grating of interest for range |
| Grating (G/mm) (others available) | 3600 | 2400 | 1800 | 1200 | 600 | 300 | 150 | 75 |
| Wavelength Range from about 105-nm to | 334 | 500 | 667 | 1000 | 2000 | 4000 | 8000 | 16000 |
| Resolution (nm) at 313.1-nm | 0.02 | 0.03 | 0.04 | 0.06 | 0.12 | 0.24 | 0.48 | 0.96 |
| Dispersion (nm/mm) | 0.9 | 1.3 | 1.7 | 2.6 | 5.2 | 10.4 | 20.8 | 41.6 |
| Available Blaze Wavelength (nm) | Holo | Holo | Holo | Holo | ||||
| 104 | 150 | 180 | 150 | 300 | 500 | 2000 | 8000 | |
| 130 | 300 | 250 | 200 | 500 | 1000 | 4000 | 12000 | |
| 240 | 300 | 750 | 2000 | 6000 | ||||
| 500 | 1000 | 3000 | ||||||
| 750 | ||||||||
| 1000 |
Focal Plane Arrays The Model 218 uses a plane grating which produces a relatively flat focal plane. It can be used with photodiode array (PDA) or CCD detectors. The focal plane lies (at a slight angle) on the same plane as the slit jaw knife edge. Extended focal length mirrors are avilable to move the focal plane outside the casting. There may be mechanical, width and mounting restrictions so please contact us to discuss the options.
| Model 218D Double Dispersion & Low Stray Light The Model 218 is available on special order as a double monochromator. Existing units can be combined and operated with independent scanning drives. Double monochromators have been built in vacuum (to 10^-6 torr) and Nitrogen purged versions. |  |