The mechanical, or stress, form of it is often used in thin-film strain gauges, and the Pockels effect, which can be used for voltage-controlled wave-plates that can quickly open and close shutters, is based on it. In the Pockels effect it is linearly proportional to an externally applied electric field. In other isotropic materials, it is proportional to the square of the applied electric field, 
The mechanical, or stress, form of it is often used in thin-film strain gauges, and the Pockels effect, which can be used for voltage-controlled wave-plates that can quickly open and close shutters, is based on it. In the Pockels effect it is linearly proportional to an externally applied electric field. In other isotropic materials, it is proportional to the square of the applied electric field, which induces anisotropies in the dielectric tensor, and this is known as the Kerr effect. The Nicol, Glan-Foucault, and Wollaston prisms all make use of it, and tetragonal, hexagonal, and trigonal crystals all exhibit this property because they are uniaxial. Resulting when a beam of light breaks up into an ordinary and extraordinary component, FTP, identify this physical effect, which occurs when a material like calcite has different indices of refraction in different directions.
The mechanical, or stress, form of it is often used in thin-film strain gauges, and the Pockels effect, which can be used for voltage-controlled wave-plates that can quickly open and close shutters, is based on it.
birefringence (or double refringence)