Abstract

The properties of the photorefractive periodic space-charge fields are traditionally investigated by measuring the diffraction efficiency of the induced phase gratings and by measuring the beam coupling and energy exchange between the two recording beams. The amplitude of the photorefractive induced space-charge field is then estimated by using involved analytical models. These methods, are in general, not particularly sensitive, and they depend on good assumed values for several material properties. In this work, we present a technique for real-time direct measurement of both the amplitude and the phase of the photorefractive space-charge fields during grating formation. The system utilizes the Doppler frequency-shifting properties of acousto-optic cells to enable the use of heterodyne detection. A network analysis is used to monitor the time development of both the amplitude and the phase of the photorefractive grating. This technique provides substantial dynamic range, and it also provides the necessary sensitivity for the detection of refractive-index changes as small as 10⁻⁸ and phase changes as small as 1°. This system has been used to characterize the photorefractive properties of LiNbO₃:Fe, KNbO₃:Fe, KNbO₃:Ta, KNSBN:Fe, and BaTiO₃. Data are presented for the buildup of the amplitude and the phase of the photorefractive space-charge fields.

© 1990 Optical Society of America