Wollaston prism

The Wollaston prism ( by William Hyde Wollaston, 1820 ) is an optical device which light by using a birefringent material ( such as calcite ), polarized (see polarizer ). In this case, the incident light is separated according to the input polarization into two orthogonal linearly polarized beams. Unpolarized, as well as circularly, or elliptically polarized light is always separated into two parts, wherein linearly polarized light, it depends on the orientation of the polarization of the optical axes of the prism.

Construction

The Wollaston prism consists of two birefringent calcite prisms, cemented together on the bottom (usually with Canada balsam or other material having a low refractive index ) to form two right triangles with perpendicular optic axes. The radiating light travels from the prism into two polarized beams apart with a deflection angle, which is determined from the corners and edges of the prisms and the wavelength of light. Commercial prisms are available with angles of 15 ° to 45 °.

Modifications

Similar prisms

By changing the prism arrays to obtain more variants for the central ray in the birefringent prisms. Depending on the arrangement for other names for prisms after the Wollaston principle have arisen, for example, the Rochon prism ( Alexis -Marie de Rochon, 1801) and Sénarmont prism ( 1857). They differ in the sense that the ordinary ray is not deflected and is achromatic. The extraordinary ray will be deflected to the side, however, depending on the wavelength of light. Sénarmonts arrangement differs from Rochons regard to the orientation of the optical axis of the second prism. Through this a simpler production from the relatively expensive material is made possible ( calcite, Icelandic spar ).

Nomarski prism

The Nomarski prism is a modified Wollaston prism, which is often found in the DIC microscopy application. Similar to the Wollaston prism, the two optical axes are oriented perpendicular to each other, but is one of the two optical axes oblique to the arrival and the opposite side of the corresponding triangular prism surface. This leads to a focal point of the two beams out of the prism, whereby a DIC microscope can be easily focused.