Quasipermanent hole-photorefractive and photochromic effects in Bi12TiO20 crystals

We report the presence of quasipermanent effects of photochromic and hole-photorefractive nature in Bi₁₂TiO₂₀ (BTO) at low irradiance at 514.5 nm. A new selective two-wave mixing (S2WM) detection technique was used that allows to separately detect phase and amplitude gratings. S2WM is used in this work for operating a self-stabilized recording setup which allows to produce unusually large quasipermanent effects. We also show that stabilized recording is necessary to obtain reliable information from hologram erasure experiments. Results reported in this paper show the complex nature of recording in BTO and the capabilities of stabilized recording and S2WM for fundamental and applied research on photorefractive crystals.