Beam amplification resulting from non-Bragg wave mixing in photorefractive strontium barium niobate

Two-wave mixing with a small angle between beams in a photorefractive crystal biased with an external electric field leads to the formation of additional non-Bragg orders and to wave amplification. A steady-state gain of 25 cm (-1) was obtained for an external voltage of 3 kV/cm in strontium barium niobate. Noise amplification and oscillation are also demonstrated.