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For
a beam of light incident on a surface at normal incidence, polarization
properties of the reflected and transmitted beams are described by
Fresnel's equations. According to these, if the angle of incidence is equal to
Brewster's angle, the degree of polarization of reflected -s beam (
perpendicular to plane of incidence ) is unity. The transmitted -p (
parallel to plane of incidence ) beam is partially polarized. Polarization
of the transmitted beam can be further purified by successive films each
of suitable thickness and refractive index so that Brewster's condition at
each interface is met. In actual practice this does not happen which
limits the performance of thin film polarizing cubes.
A cube optical isolator is made of a
narrow band thin film polarizing cube cemented to a quarter wave plate
with its fast axis at 45 degrees azimuth to the output -p polarization of
the cube. The quarter waveplate is either a mica cemented between glass
plates or zero order cemented crystal quartz type. Standard wavelengths
for which the isolator is optimized are 441, 488, 515, 530, 633, 1060 and
1300 nm. All the outside faces of the device are V type anti-reflection (
less than .25% per surface ) coated for the specified wavelength. Please
visit our Anti-Reflection Coating page on this website for various
reflectivity plots. A dot marked on a polarizing cube indicates the 90
degree prism the diagonal of which has more than 20 layers of polarizing
coating. For optimum performance, the prism with the dot should be on the
input side. Standard isolators are available in 12 and 25 mm cube sizes.
Other sizes are available on special order.
A cube beam displacer is made of two
narrow band polarizing cubes cemented to each other. The reflected -s
polarization from the first cube is reflected again by the second cube and
exits parallel to the output -p polarization from the first cube. Standard
wavelengths for which the isolator is optimized are 441, 488, 515, 530,
633, 1060 and 1300 nm. All outside faces of the device are V type
anti-reflection ( less than .25% per surface ) coated for the specified
wavelength. Please visit our Anti-Reflection
Coating
page on this website for various reflectivity plots.
The polarizing cubes are made of two 90 degree prisms. The prism with the
dot as shown has the polarizing coating on its diagonal and should be on
the input side of the beam for optimum performance.
Standard beam displacers are available in 12 and 25 mm cube sizes. Other
sizes are available on special order.
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