CRYSTAL QUARTZ WAVEPLATES

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. its dependence on wavelength, there is a variation of retardation with wavelength. In a crystalline quartz zero-order double plate waveplates, variation of retardation with wavelength is less than in multi-order single plate type. This dependence becomes greater at shorter wavelengths. A zero order double plate retarder is made of two plates of crystal quartz with fast axes at 90 degrees to each other. The thickness difference of the two gives the desired zero order retardation at a desired wavelength. A multi order waveplate gives several full waves and a desired fraction ( e.g. quarter or half ) of a wave of retardation at a desired wavelength.

Zero and multi-order quarter or half waveplates for a specified wavelength from 250 to 1600 nm are available in standard clear aperture diameters of 12 mm and 22 mm. These are cemented, optically contacted or air-spaced. Other clear apertures including eighth wave retarders are available on special order.