Electro-optic devices used for building modulators.
A Pockels cell is a device consisting of an electro-optic crystal (with some electrodes attached to it) through which a Light beam can propagate. The phase delay in the crystal can be modulated by applying a variable electrical voltage. The Pockels cell thus acts as a voltage-controlled waveplate. Pockels cells are the basic components of electro-optic modulators used for Q Switching lasers.