The reference beam used to retrieved the recorded information, also excites the donor electrons and disturbs the equilibrium of the space charge file in a manner that produces a gradual erasure of the recording. Another problem is that lithium niobate is very sensitive to changes in temperature. At higher temperatures, data written in the medium can become permanent. The very technique of multiplexing used to increasing the capacity has posted a problem as well. The increased numbers of multiplexed holograms decrease the diffraction efficiency of the lithium niobate.
Diffraction efficiency is inversely proportionate to the number of multiplexed holograms.
If the diffraction efficiency is too low, noise become a problem. The noise occurs from the fluctuations in the illumination of the laser, scattering from the crystal, and many other sources, it makes the reconstruction of the holograms too weak to be detected. Without solving those problems, holographic storage cannot be used reliably. Lucent Technologies' Bell labs researchers discovered a photopolymer in early 1990s that has more sensitivity and better dynamic range than the lithium niobate that had been used for roughly 30 years. The material has been tested and improved over the years.