Abstract
When a hologram is recorded in a photorefractive material by two beams, one of which is periodically phase modulated (with amplitude Θ and frequency Ω), the output signal in a two-wave mixing configuration contains two temporal harmonics with amplitudes UΩ (at Ω) and U2Ω; (at 2Ω) . The origin of U2ω in the case when the drift mechanism prevails and the diffusion mechanism is negligible is associated with the phase shift Δ between the interference pattern and the holographic grating. The value of Δ is determined by tgΔ = [Illegible] where E is the external field and Eq is the saturation field, E [Illegible] where NA is the trap concentration, e is the electron charge, ε is the dielectric constant, and K is the grating wave vector. It follows from [1] that U2Ω/UΩ = J2 (Θ) [J2 (Θ)]-1 tgΔ, where J. and J2 are Bessel functions. The experimental measurements of the ratio U2ω/Uω allows one to find E[Illegible] and NA. This technique was used to measure E[Illegible] and NA in many samples of [Illegible] and [Illegible]. The values of NA were found to be of the order of 10[Illegible] cm-3 for BSC and of the order of 10[Illegible] cm-3 for BTO, consistent with the available literature data obtained by other technique.
© 1998 IEEE
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