We have demonstrated that fixation and erasure of phase holograms in ferroelectric materials can be achieved by fast electrical control. High ionic mobility that allows the change of the electronic pattern into a stable ionic one is obtained by applying, during 0.1 sec, an external field slightly smaller than the coercive field to the crystal. Erasure is accomplished in 3 sec by applying a field that causes saturation of the polarization. Investigation of this process was carried out in BaTio3 crystals doped with Fe.
We demonstrate that the electrical fixation of holograms recorded in (Sr0.75Ba0.25)Nb2O6 involves local polarization switching; the fixing threshold is found to be nearly the average coercive field Ec = 970 V/cm, and the minimum fixing time is the polarization switching time. The diffraction efficiency enhancement of fixed holograms is attributed to the photoinduced space charge field's overcancellation by ionic displacements associated with the polarization switching.
An apparatus permitting high accuracy measurements of fast variation of birefringence in various media has been built using the following principle. A feedback loop cancels automatically the corresponding rotation of the light polarization vector by a calibrated voltage change applied to a KDP crystal. It has been used to measure the optical damage effect in electro-optic crystals such as LiNbO3.
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