Resonant two-photon photorefractive grating in praeseodymium-doped strontium barium niobate with cw lasers

We report experimental observation of resonant two-photon photorefractive gratings in Pr-doped SBN:60. Long-lived 4f intermediate states significantly reduced intensity threshold, thus permitting use of cw lasers for the two-photon transitions. Both two-beam one-color two-photon gratings and three-beam two-color gratings were observed. We expect these results to be extended to other rare-earth dopants.