Question

working principle of a
Babinet's compensator​

Answer 1

Answer:

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Explanation:

Answer 2

A Babinet–Soleil compensator (or sometimes just Babinet compensator) is essentially a combination of birefringent plates which can be used as an adjustable waveplate (retarder plate). It contains three birefringent plates (see Figure 1), all made from the same material (e.g. crystalline quartz): one plane-parallel plate and two wedges, where the latter have an orientation of the optical axis perpendicular to that of the plane-parallel plate. One of the wedges can be moved in a direction perpendicular to the beam, so that the effective thickness is adjustable. Usually, one uses a translation stage with a micrometers screw for moving that wedge. There are also motorized versions which can be computer-controlled.

Babinet-Soleil compensator

Figure 1: Babinet–Soleil compensator, made from three birefringent plates.

If the insertion of the movable wedge is adjusted such that the overall optical path length in the wedges is the same as in the plane-parallel plate, one obtains overall zero retardance, i.e., no changes of polarization direction of a beam. By moving the which somewhat in or out, a retardance of either sign can be obtained in a certain range, e.g. ±λ. The device can act an effective zero-order waveplate with a tunable degree of retardation. That works in a wide range of optical wavelengths.

The wedge angles are made so small that there is (in contrast to a Wollaston polarizer) no substantial spatial separation of polarization components, i.e., no significant transverse beam offset. Note also that although the optical path length in a single wedge depends on the transverse position, that is not the case for a pair of wedges. Therefore, one can obtain uniform retardance over a large aperture. There is also no significant beam deflection if the plates are made with sufficiently high precision.

Although the Babinet–Soleil compensator can be used in a wide range of wavelengths, note that there is some wavelength dependence of the obtained retardance.

The plates often have anti-reflection coatings in order to minimize reflection losses and avoid interference effects.

Compensators are available for different wavelength regions, including the

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