An electrooptical effect in which the application of an electric field produces a birefringence which is proportional to the field. Only crystals which lack a center of symmetry (20 out of the 32 classes) may show this effect. (These are, incidentally, the same classes which are piezoelectric). The Pockels cell is used in ultrafast shutters. For the longitudinal arrangement, the phase shift is given by
where is the electrooptical constant measured in m/V.
