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When
any form of polarized light is incident on a birefringent waveplate, it is
resolved into two linearly polarized components which vibrate
perpendicular to each other and travel with different velocities in the
crystal. The beams emerge with a phase delay. This phase delay or
retardation is dependent on birefringence of the crystal. Birefringence at
a specified wavelength is the difference in refractive indices of the
extraordinary and ordinary resolved components. Because of dispersion of
birefringence i.e. it's dependence on wavelength, there is a variation of
retardation with wavelength.
Quarter and half wave mica waveplates are available as a thin cleaved zero
order retarder at a specified wavelength between 450 to 1600 nm cemented between
BK7 glass plates or as bare mica, V type anti-reflection coated and
mounted in a cell. Mica is a bi-axial, optically inactive crystal which
has about 3 to 5 % absorption in the visible region of the spectrum. The
cemented mica retarders are available in clear aperture diameters of
10 and 22 mm while bare mica retarders are available in a clear aperture
diameter of 25 mm only. Special sizes are available upon request.
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