Babinet–Soleil compensator

A Babinet compensator ( after the French physicist Jacques Babinet ) is mainly used in microscopy, optical component that introduces a continuously adjustable phase shift between various polarized components of light. This is the essential advantage compared to wave plate, which (for example ) results in a fixed phase shift.

Design and operation

The Babinet compensator consists of two wedges, the birefringent material (e.g., calcite ), whose optical axes are perpendicular to each other. The differently polarized components of the incident light is delayed in two different keys. Shifts to the two wedges together, so the optical path length in the birefringent material and thus the phase shift between the ordinary and extraordinary rays is changed. In contrast to the Wollaston prism, which works on the same principle, the Babinet compensator has such a small wedge angle ( about 2.5 ° ) that the spatial shift between the ordinary and extraordinary rays in each case does not matter.

The phase shift arises from the thicknesses and the wedges and the refractive indices for ordinary and extraordinary beam and:

A Babinet compensator is used because of the variable effective thickness () for different wavelengths, while strictly speaking wave plate deliver only one wavelength, the exact phase shift, since their thickness is fixed.