An Etymological Dictionary of Astronomy and Astrophysics
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A crystal device made of two → quartz  → prisms with equal acute angles assembled in a rhombus that is used in analyzing → polarized light. The wedge-shaped prisms are placed against each other and can be displaced along their plane of contact by a → micrometer. Thus they form a parallel plate of variable thickness allowing the optical retardation to be adjusted.

Jacques Babinet (1794-1872), French physicist; → compensator.

One who, or that which, compensates.

→ compensate; → -or.

A transparent plate inserted in one of the arms of an interferometer, in particular the → Michelson interferometer, to compensate for a longer → optical path in the other arm. Its function is to ensure that the beams transverse the same total thickness of glass in both arms of the interferometer. This is not essential for producing → interference fringes in monochromatic light. The compensator plate is of the same glass and the same thickness as the → beam splitter plate.

→ compensator; → plate.

An optical compensator which produces a constant phase change over the entire field, as opposed to the phase change produced by the → Babinet compensator, which occurs progressively across the field. The compensator consists of two wedges of the same wedge angle and a parallel plate. The optic axes of the two wedges has the same orientation. These form a variable thickness plate. One of the wedges is assembled to the fixed parallel plate. The optic axis of the parallel plate is at 90° to that of the wedges. The other wedge is attached to a micrometer and moves to produce a thickness difference between the fixed and variable thickness plates, thus producing a phase delay.

Jean-Baptiste Soleil (1798-1849); → compensateur.