Quartz Crystal (SiO2) for infrared polarisers0 pages
Crystal Quartz Polarizers for the Infra-Red
Waveband ^^^-^^
Knight Optical can offer Crystal Quartz (Si02) Polarizers for Infra-red systems over the
waveband of 0.2 to 2.3um. Crystal Quartz is a birefringent material that makes it useful for
polarizers and waveplates. A typical arrangement for laser polarizers is in the Wollaston
Prism is a polariser using Crystal Quartz. The Wollaston consists of two prisms that are
cemented together and the two output rays, the s and p polarisation, are deviated nearly
symmetrically within a degree or two.
The deviation is about ±1° at 2.3um and increases as the
wavelength is reduced, about ±3° at 200nm.
The clear aperture is about 10mm in diameter with
a wavefront distortion that is less than one quarter
of a wave at 633nm. Wollaston Prisms' are used in
spectrometers and other optical arrangements to
separate, or combine, the s and p polarizations. The
extinction ratio is 100,000:1.
The Rochon is another configuration that uses
crystal quartz for depolarizers as in the figure below.
The Rochon operates by having the ordinary and
extraordinary rays propagate co-linearly along the optic
axis of the first prism.
Upon entering the second prism the ordinary ray 'sees'
the same refractive index and thus continues undeviated
at this interface. However, the extraordinary beam now
'sees' a lower refractive index and is thus refracted at the
interface.
The angle of refraction is further increased at the exit
surface. It is possible to have tune the separation angle
at a specific wavelength within the limits for crystal
quartz, which is 1.46° at 200nm and 1.00 at 2um. The
extinction ratio is 100,000:1 as with the Wollaston prism.
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