Method for measuring off-diagonal Kerr coefficients by using polarized light transmission

We report a method for measuring the off-diagonal coefficients of the quadratic electro-optic (Kerr) tensor by using polarized light transmission. The method relies on designing an experimental configuration in which the linear electro-optic (Pockels) effect does not contribute to the data. Our method can be used to obtain off-diagonal Kerr coefficients for all but two of the 20 crystal point groups for which the Pockels effect and the Kerr effect coexist. Our theoretical model includes effects from transmission, multiple reflections, and electrostriction but neglects absorption in the crystal. To verify the method, we used it to measure the R12 and R13 Kerr coefficients for a (100)-type single crystal of ferroelectric barium titanate (BaTiO3) at room temperature (23.5 degrees). To our knowledge, this is the first time this method has been used and the first time these coefficients have been measured for the unclamped crystal in the tetragonal state. The mean values obtained with this method are R12 = -3.5+/-0.3 x 10(-17) m2/V2 and R13 = -8.0+/-0.7 x 10(-17) m2/V2.