Method of measuring the exponential gain coefficient in codirectional photoreactive two-wave mixing at intermediate regime

We present a method of measuring the parameters of a photorefractive crystal in codirectional two-wave mixing that is suitable for two-wave mixing in the intermediate regime (before saturation). Three parameters of a crystal, the saturation exponential gain coefficient, saturation intensity and intensity absorption coefficient, can be measured simultaneously by using the method. The contribution of the intensity dependence of intensity absorption coefficient is also considered. The three parameters of a BaTiO3 crystal are measured and the measured data are checked by another independent measurement.