The Effect of Large Signals in Photorefractive Media

Photorefractive materials remain of interest as optically nonlinear elements, because of the large saturated nonlinear effects that they exhibit at low continuous wave optical power levels. They can be used to give large optical amplification to image bearing beams by utilising the nonlinear process of two-wave mixing. Four-wave mixing can also be achieved, and phase conjugate reflectivities of signal beams can be substantially greater than unity. Self-pumped phase conjugation is also possible in those photorefractive materials with nonlinearities that are suitably large.