Lifetimes of thermally fixed holograms in LiNbO(3):Fe crystals

The thermal erasure decay at different temperatures of holographic gratings thermally fixed in iron-doped lithium niobate has been exhaustively studied. An activation energy of 0.94 eV was found to be independent of the grating fringe spacing. At a given temperature the decay time is strongly dependent on the grating spacing. This dependence is well fitted to a square fringe spacing law, as predicted theoretically. From the experimental data the room-temperature hologram lifetime under illumination is extrapolated, giving as a result t(years)=(5.2+/-0.2)?(2) , with the grating spacing ? in micrometers.