MCS260
CORNERSTONE 260 MONOCHROMATORS
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7 MONOCHROMATOR RESOLUTION
Gratings are available in various groove densities (i.e. lines/mm). Higher groove densities give higher
reciprocal dispersion and therefore higher resolution. The monochromator bandpass with a 1200
lines/mm grating is half that of the same arrangement with a 600 lines/mm grating. Note that this simple
relationship is not accurate for slit widths below 50 µm, as the optical aberrations begin to play a role in
the bandpass and resolution.
Using a grating with a high groove density may increase resolution, but the spectral range narrows. The
dispersion of a grating changes inversely with the groove density. If the groove density is halved, the
dispersion is doubled. A monochromator mechanism can only tilt the grating through a limited range of
angles. The angle and groove density determine the transmitted wavelength.
The gratings can be tilted to 0 degrees, so the lowest possible wavelength for a UV grating is set by the
transmittance of air at about 180 nm. The ability to output wavelengths below 180 nm is also dependent
on the efficiency characteristics of the grating.
The following graphs are intended to illustrate the effects of slit width selection, in terms of throughput and
resolution. This data was taken using Oriel’s Tunable Light Source (TLS) systems, using various slit
widths to change the resolution. The TLS systems employ a Cornerstone 130 monochromator.
However, the concept of resolution vs. slit width is the same for the Cornerstone 260 monochromators.
Figure 19: Resolution vs. Throughput
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