Dynamics of photodeformations and space charge field in photorefractive Fe : Li Nb O 3 studied with synchrotron area diffractometry

The method of synchrotron area diffractometry has been used to map with a high spatial resolution in real time the distribution over the crystal surface of the lattice deformation tensor components induced by a macroscopic visible light beam on a z -cut iron-doped photorefractive Li Nb O 3 crystal. The xy planes exhibit a tensile strain, on the order of 10 − 4 , in the center and long range, extending up to 780 μ m , shear deformations at the borders of the illuminated region, respectively. Photodeformations evolve with illumination time with relaxation type, time dependence, and time constants of the order of minutes. The observed lateral distribution of deformation tensor components, as well as their temporal evolution, has been examined, considering the coupling of the converse piezoelectric effect with the strong space charge field generated by the damage inducing beam along the z axis due to the bulk photovoltaic effect. The observed strain in the center can be attributed to the bulk photovoltaic field of the order of 10 7 V ∕ m , while the long range shear deformations are mainly associated with the lateral components of the electric field which are present at the borders of the space charge regions. Both photodeformations and space charge field evolve at the same time scale, the dependence of time constants on the incident light intensity following the predictions of the one-center model charge redistribution due to the bulk photovoltaic effect. This work demonstrates that the method of synchrotron area diffractometry is a very powerful tool to study in situ the dynamics and spatial variation of microstuctural changes (deformations) induced by an external field (electric, magnetic, or temperature).