Babinet compensator

A Babinet compensator (after the French physicist Jacques Babinet ) is mainly used in the microscopy used optical component comprising a continuously adjustable phase shift between different polarization introducing components of light. This is the main advantage compared to lambda plates , which cause a fixed phase shift (e.g. ). ${\displaystyle \lambda /4}$

Structure and functionality

Babinet compensator

The Babinet compensator consists of two wedges of birefringent material (e.g. calcite ), the optical axes of which are perpendicular to each other. The differently polarized components of the incident light are delayed differently in the two wedges. If the two wedges are shifted against each other, the optical path length in the birefringent material and thus also the phase shift between ordinary and extraordinary rays are changed. In contrast to the Wollaston prism , which works on the same principle, the Babinet compensator has such small wedge angles (around 2.5 °) that the spatial shift between the ordinary and extraordinary rays does not matter.

The phase shift results from the thicknesses and the wedges and the refractive indices for ordinary and extraordinary rays and : ${\displaystyle \Delta \varphi }$ ${\displaystyle d_{1}}$ ${\displaystyle d_{2}}$ ${\displaystyle n_{o}}$ ${\displaystyle n_{ao}}$

${\displaystyle \Delta \varphi ={\frac {2\pi }{\lambda }}(d_{1}-d_{2})(n_{o}-n_{ao})}$

Because of the variable effective thickness ( ), a Babinet compensator can be used for different wavelengths , while lambda plates, strictly speaking, only provide the exact phase shift for one wavelength, since its thickness is fixed. ${\displaystyle d_{1}-d_{2}}$ ${\displaystyle \lambda }$ ${\displaystyle d}$

Individual evidence

1. ↑ Eugene Hecht: Optics . Oldenbourg, 2005, ISBN 978-3-486-27359-5 , pp. 574 ff . ( limited preview in Google Book search).