MCS260
CORNERSTONE 260 MONOCHROMATORS
26
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 are
used to define parallel and perpendicular.
The graphs for the Cornerstone 260 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 an Oriel sales engineer for more information on
the effects of polarized light in terms of grating efficiency.
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