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 U_Ω (at Ω) and U_2Ω; (at 2Ω) . The origin of U_2ω 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 E_q is the saturation field, E [Illegible] where N_A 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 U_2Ω/U_Ω = J₂ (Θ) [J₂ (Θ)]^-1 tgΔ, where J. and J₂ are Bessel functions. The experimental measurements of the ratio U_2ω/U_ω allows one to find E[Illegible] and N_A. This technique was used to measure E[Illegible] and N_A in many samples of [Illegible] and [Illegible]. The values of N_A 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