Abstract

We present observations of wave focusing and defocusing in a photorefractive Ba_0.77Ca_0.23TiO₃ (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 N_eff ≈ 1.3⋅10²⁰ m⁻³ as well as to find the thermal excitation cross-section β_T ≈ 1.8⋅10⁻¹⁴W of the crystal. Light intensity and wavelength are correspondingly 3 mW and 633 nm.

© 2003 Optical Society of America