We present observations of wave focusing and defocusing in a photorefractive Ba<sub>0.77</sub>Ca<sub>0.23</sub>TiO<sub>3</sub> (BCT) crystal without external electric field and without background illumination. The effects depend on the cross-section of the input beam. We show that by decreasing of the diameter of the input beam the fanning effect disappears at 150 µm. The self-focusing is observed for input diameters from 150 µm down to 40 µm, the self-defocusing is observed for input diameters from 40 µm down to 20 µm. For diameters smaller than 20 µm no non-linear effects are observed. The 1D self-trapping is detected at 65 µm in BCT. The experimental results are used to estimate the effective density of ionized donors <i>N</i> <sub>eff</sub> ≈ 1.3 •10<sup>20</sup> <i>m</i> <sup>-3</sup> as well as to find the thermal excitation cross-section β<sub> <i>T</i> </sub> ≈ 1.8 •10<sup>-14</sup> <i>W</i> of the crystal. Light intensity and wavelength are correspondingly 3 mW and 633 nm.

© 2003 Optical Society of America

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