We propose an optical method for determining the value of the coercive field in a ferroelectric crystal. The experiment is carried out in photorefractive Sr0.60Ba0.40Nb2O6 (SBN:60), where the crystal is used as a Fabry-Perot interferometer. An extraordinarily polarized He-Ne beam enters the a face of the crystal, while a single 20 V/s triangular electrical pulse (from 0 to 1.9 kV) is applied to the crystal along the caxis and opposite to the direction of the initial poling field. We describe how the number and direction of fringe shifts with respect to the applied field is used to obtain the value of the coercive field. We find the coercive field value of SBN:60 to be 1.55 kV ± 20 V. We present a similar technique, using an electric pulse in the same direction as the initial poling field to measure the electro-optic coefficient of the crystal. We measure a value of 147 ± 6 pm/V for the r33 coefficient at 632.8 nm.
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