Sublinear photoconductivity and the photorefractive effect

The photorefractive effect is a nonlinear optical phenomenon in which mutually coherent waves interact in a photoconducting electrooptic material in a manner akin to real time holography or phase conjugation. The strength, or maximum diffraction efficiency, of the photorefractive effect is in dependent of intensity and has been observed with nanowatts of total power, given sufficient buildup time. The speed of hologram formation is proportional to the photoconductivity of the material used and high speed photorefractive devices will require higher optical power, although the choice of material plays a large role as well.