Contradirectional two-beam coupling in absorptive photorefractive materials: application to Rh-doped strontium barium niobate (SBN: 60)

Contradirectional two-beam-coupling gains are measured in Rh-doped strontium barium niobate (SBN) as a function of the Rh concentration and the incident pump–probe beam ratio. These measurements indicate that larger two-beam-coupling coefficients in this contradirectional geometry (as large as ∼16 cm−1) are typically linked to stronger optical absorption in the more heavily doped samples. The effects of such strong absorption are explicitly included in a theoretical analysis applied to the measured data. In particular, earlier theoretical treatments of this two-beam-coupling process with nonnegligible absorption are extended to yield an approximate expression for the probe gain. The accuracy of this analytic expression is then verified by comparison with exact numerical results as well as with experimental measurements in the Rh-doped SBN samples. Further experimental and theoretical comparisons are made after the contradirectional two-beam-coupling process is related to asymmetric transmission through a photorefractive window (i.e., one-way glass), again in the presence of strong absorption.