Persistent holograms are recorded with red light in lithium niobate crystal
s doped with manganese and iron. We find that the oxidation/reduction state
of the crystal has a profound impact on the recording and readout performa
nce. The underlying physical processes are investigated and the recording a
nd readout responses are explained and optimized. (C) 1999 American Institu
te of Physics. [S0003-6951(99)05325-5].