The transfer function and impulse response of photorefractive two-beam coupling

The transfer function and impulse response of photorefractive two-beam coupling are derived in the undepleted pump approximation. For sufficiently strong coupling ΓL, the impulse response features a broad delayed output pulse. In the limits of negligible and strong absorption αL, this coupling threshold reads ΓL_thr=4 and Γ_thr=2α, respectively. The time delay and pulse height are functions of the coupling ΓL, the photorefractive time constant τ, and the effective absorption αL. Experiments on a BaTiO₃ crystal measuring the absoluted square of its transfer function and the impulse response are used to determine the coupling and time constant