Holographic storage dynamics in lithium niobate: Theory and experiment

We present a theoretical model that describes holographic ionic fixing and storage dynamics in photorefractive crystals. Holographic gratings that are based on charge redistribution inevitably decay because of ionic and electronic conduction. Relevant decay rates and transient hologram field expressions are derived. Ionic gratings are partially screened by trapped electrons on readout. The lifetimes of fixed ionic holograms are limited by the finite ionic conductivity at low (i.e., room) temperatures. Only under certain and restricted conditions can these decay times be acceptably long. A significant increase in fixed ionic hologram lifetime is realized in lithium niobate with a low hydrogen-impurity content. The residual ionic conductivity (decay-time constant) in these samples exhibits similar to 1.4-eV activation energy and is not due to protonic conduction. Fixed hologram lifetimes of similar to 2 years at room temperature in dehydrated lithium niobate crystals are projected. (C) 1996 Optical Society of America.