| Popis: |
The optical response of the photorefractive crystals KNbO3:Ta, KNbO3:Fe, LiNbO3:Fe, and nominally pure BaTiO3 is investigated. In the experiment, a holographic grating is built in the crystal under investigation via a two-wave mixing scheme that utilizes the signal-processing capacities of two acousto-optic Bragg cells. The dynamic interaction of the Bragg cells with the photorefractive grating causes a heterodyned RF signal to appear on the output laser beam, enabling the real-time, direct measurement of the amplitude and phase of the space-charge fields in the crystal. Experimental results are presented for the amplitude and phase of the space-charge fields, the diffraction efficiency, and the grating time constant as a function of spatial frequency. Quantitative understanding of some of the fundamental processes and material properties responsible for the optical response is gained through comparison of the measured data to theoretical models. In this analysis, the diffusion and photovoltaic transport lengths, Debye screening length, net trap concentration, and net conductivity factor are determined. |
