MCS260B
CORNERSTONE 260B MONOCHROMATORS
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6.3 POLARIZATION EFFECTS
The diffraction efficiency from a grating usually depends on the polarization of the radiation
incident on the grating. There can be significant differences between the efficiency for radiation
with the electric field vector parallel to the grating grooves and radiation with the electric vector
perpendicular to the grooves.
Radiation with the electric vector restricted to a specific direction is linearly polarized. Linearly
polarized radiation with the electric vector parallel to the grooves is P-polarized. Radiation
polarized perpendicular to the grooves is S-polarized. For
Oriel’s monochromators and
spectrographs, P-polarized radiation has the polarization axis parallel to the entrance slit. In most
laboratory applications with the instrument sitting on its mounting surface on a horizontal bench or
optical table, P-polarized radiation is vertically polarized.
Note: this definition of S- and P-polarization for diffraction gratings does not follow the general
rules for S and P-polarization for optics where the plane of incidence rather than the grooves is
used to define parallel and perpendicular.
The graphs for the Cornerstone 260B configurations have one efficiency curve per grating. This is
representative of 45-degree polarization, which is the average of the P-polarization and S-
polarization efficiency curves.
Typically, the efficiency curve for P-polarized light peaks slightly lower than the nominal blaze
wavelength and smoothly declines to 0% at about three times the blaze wavelength. The curves
for P-polarization are generally smooth, without dramatic changes in direction or sharp features.
The curves for S-polarized light peak slightly above the nominal blaze wavelength and decline.
However, the efficiency can recover dramatically and show good efficiency over a broader
wavelength range. The S-polarization curves can show sharp features (anomalies) which
complicate data deconvolution from spectral scans.
If a source is being measured close to an anomaly, then the real feature may be dramatically
distorted. If possible, a grating should be selected (or polarization) which has no significant
anomaly in the spectral region of interest. Contact a Newport sales engineer for more information
on the effects of polarized light in terms of grating efficiency.
6.4
OPTIONAL DIFFRACTION GRATINGS
There are a wide range of diffraction gratings available from Newport that are compatible with the
CS260B monochromator. The following gratings (Figure 21) can be installed in either the dual or
quad grating mount. Contact a Newport sales engineer or visit the Newport website for more
information on selecting the appropriate gratings and configuring a custom monochromator.
