Influence of the photovoltaic effect on optical limiting with lithium niobate

Fe:LiNbO3 in a simple focal plane geometry has demonstrated efficient optical limiting through two-beam coupling. The magnitude of the observed optical limiting implies an optical gain coefficient which greatly exceeds that predicted by standard photorefractive diffusion theory. Experimental measurements have confirmed that the optical gain coefficient is approximately five times grater than can be accounted for through normal charge diffusion. The photovoltaic effect has been identified as the most likely mechanism for generating the observed high optical gain. We have made a direct observation of the role of the photovoltaic effect in counter-propagating two-beam coupling in photorefractive iron doped lithium niobate. We have found experimentally that the photovoltaic effect is indeed the dominant mechanism for two beam coupling in an optical limiting geometry. The contribution to optical limiting from the photovoltaic effect is approximately five times greater than that arising from diffusion mechanisms alone, in agreement with earlier optical gain measurements.