Photovoltaic contribution to counter-propagating two-beam coupling in photorefractive lithium niobate

A direct observation of the role of the photovoltaic effect in counter-prop agating two-beam coupling in photorefractive iron-doped lithium niobate has been made. Through the application of a strong external field we directly observe that the photovoltaic effect is the dominant mechanism for a counte r-propagating two-beam optical limiting geometry. We find that the contribu tion to counter-propagating two-beam coupling gain coefficient from the pho to-voltaic effect is approximately five times greater than that arising fro m diffusion mechanisms alone. (C) 2001 Published by Elsevier Science B.V.