780 nm near-infrared photorefractive holograms recorded in undoped Bi12TiO20 crystal under the action of external electric field

In this paper, we studied recording and erasure of photorefractive holographic gratings recorded at 780 nm in an undoped Bi12TiO20 (BTO) crystal sample under the action of an externally applied electric field. The diffraction efficiency was measured by directly chopping the diffracted beams by the gratings recorded in a two-wave mixing setup without using of any phase-modulation technique of the recording beams or feedback mechanism. An enhancement of 3.5-fold in the diffraction efficiency was observed when the applied electric field increased from 0 to 6 kV/cm. The theoretical dependence of the diffraction efficiency on the external electric field considering the effect of screening of charges near the electrodes was investigated, and the result is supported by good fit to the experimental data, allowing us to compute characteristic parameters of the material, including the values of photoactive donor concentrations (ND1)eff ≈ 0.12 × 1016 cm−3 and (ND2)eff ≈ 0.8 × 1015 cm−3, respectively, for the levels placed at 1.6 eV and 1.3 eV below the conduction band responsible for photorefractive recording in the BTO sample.