Comparison of photorefractive beam fanning using monochromatic and achromatic two-wave mixing in SBN

Beam fanning is examined as a noise source in monochromatic and achromatic two-wave mixing. We show that fanning acts mainly as a parasitic loss for low beam ratios, whereas it contributes a background noise floor for high beam ratios. In the first regime, fanning loss is much smaller in achromatic two-wave mixing than in the monochromatic case.