Charge–carrier diffusion length in photorefractive crystals computed from the initial hologram phase shift

The phase shift between the pattern of light onto a photorefractive crystal and the resulting hologram at the very beginning of the recording process in two-wave mixing is analyzed and measured as a function of the applied electric field. These data allow one to compute the diffusion length of photoexcited charge carriers and to evaluate the actual electric field inside the crystal. A diffusion length of 0.14 μm is measured in a nominally undoped photorefractive Bi12TiO20 crystal using a 532 nm wavelength laser illumination, in agreement with results obtained from other methods.