We present a simple method for suppressing fluctuation of the space-charge
field in a photorefractive wave-mixing system. The method can be applicable
to any type of such a system, such as two-wave mixing and four-wave mixing
. In this method an external illuminating intensity, which is incoherent wi
th the interacting beams, is turned on or off according to the sign of the
deviation of the photorefractive output from a set value. The set value can
be chosen from a wide range. (C) 2001 Optical Society of America.