Evidence of electron compensation in a LiNbO3:Fe holographic optical filter

We present experimental evidence of electron compensation of a fixed ionic hologram in a photorefractive iron doped lithium niobate crystal. When the hologram is stored in the dark, the fixed hologram diffraction efficiency decreased from 20% to 6% in a 15 day period. 30 J/cm/sup 2/ of 488 nm wavelength uniform illumination was required to mitigate the electron compensation and restore the diffraction efficiency to 20% (reveal the fixed ionic grating).