Hologram enhancement in photorefractive media

We consider the possibility of restoration and/or enhancement of decaying holograms in photorefractive media by using a simple optical readout in conjunction with a phase conjugator. The results indicate that extremely weak holograms can be enhanced provided that the two-beam coupling is sufficiently strong. Steady-state photorefractive holograms can be maintained continuously without decay by using a properly designed readout scheme. The result also provides an explanation for the formation of mutually pumped phase conjugation in terms of the amplification of initial noise gratings.