Rochon & Wollaston Beamsplitters
Rochon
and Wollaston beamsplitters consist of two prisms of calcite cemented together
in such a way as to separate the s- and p- components of polarisation and make
them emerge at an angle to each other. These
prisms have a length/aperture ratio
of one. In the case of the Rochon
beamsplitter the p-component is un-deviated while the Wollaston produces a
symmetrical split of the two components. A
small (5°) separation of the two beams is produced by the Rochons, while
Wollastons provide larger angles of separation, typically 10° or 15°.
The
Calcite used in these prisms is available in several different grades.
Optical grade calcite, which has few inclusions and shows no scattering
when viewed under a 40 watt incandescent lamp, is normally used.
However, for application with lasers it is recommended to use laser grade
calcite. This grade of calcite
exhibits no scattering when illuminated with a helium neon laser beam.
For situations in which scattering is unimportant a standard grade of
calcite may be used.
Rochon
& Wollaston beamsplitters are normally supplied as square cross section
prisms with an aperture of 5, 8, 10, 15 or 20 mm.
They are mounted in an absorbing black potting compound within a metal
cell.
Single
layer MgF2 anti-reflection coatings may be applied if required. These coatings provide a reflectance of less than 2% over a
range of 220-400 nm, 400-700 nm or 700-1100 nm.