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>
<sup>-3</sup> as well as to find the thermal excitation cross-section β<sub>
</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