Optical properties of uniaxial trigonal crystals of 3m point group symmetry under an applied electric field along x principal axis

Pockels activity in uniaxial trigonal crystals with 3m point group symmetry is investigated under an electric field applied along x principal axis. As the result, the uniaxial crystal deforms into a biaxial one exhibiting three distinct refractive indices. One principal axis is shown to lie almost along the optical axis. The remaining two principal axes are rotated by about 45 degrees along perpendicular directions to the optical axis. Under application of the electric field, an x polarized plane-wave light, is shown to rotate as it propagates along the optical axis. The length for 90 degrees rotation is determined. Practical applications are mentioned.