Optics 101

The Pockels Effect

The Pockels effect explains the influence of an electric field on a non-linear material in causing birefringence or altering the existing birefringence. This was first discovered by Friedrich Pockels in the year 1893. Some of the materials that exhibit the Pockels effect are ammonium dihydrogen phosphate, potassium dihydrogen phosphate, lithium tantalite and cadmium telluride.

Pockels discovered that certain materials tend to become birefringent or alter their birefringence when an electric field is applied. This effect is not observed in all materials - materials that have inversion symmetry do not exhibit this effect. This article will elaborate on the working, experimental set up and applications for Pockels effect.

Experimental Set Up

Materials that show the Pockels effect are called Pockels media. Devices that are made from Pockels media are called Pockels cells. Pockels cells are wave plates whose voltage can be controlled. A Pockels cell is made up of two crystals, placed facing each other, thus forming a zero order wave plate in the absence of voltage.

The electric field is applied in a direction that is transverse to the light beam direction. The electrodes in the form of rings are positioned at the ends of the crystal.

Working Principle

Pockels effect is brought about by the application of an electric field on a non-linear material. Pockels effect is the production of birefringence or the change on birefringence of a non-linear material by the application of an electric field.

Birefringence is a type of optical anisotropy, or non-linear optical behaviour. Birefringent materials have a refractive index which depends on the polarization state and progapation direction of the incident light.

Applications

Some of the applications of Pockels cells are listed below:

  • Electro-optic modulators
  • Creation of amplitude or phase modulated beam
  • Preventing feedback of a laser cavity
  • Optical video disc mastering system.

References

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