Anisotropic Self-diffraction Research Articles

Anisotropic self-diffraction in Mg-doped LiNbO3

The characteristics of anisotropic self-diffraction were studied for undoped LiNbO3 crystals and LiNbO3:Mg at doping levels of a few mole percent. From the absolute magnitude and the time dependence of the signal, it was possible to determine the induced refractive-index change and the conductivity of the charges involved in the photorefractive effect for each sample. For these excitation conditions, only charge migration perpendicular to the c axis contributes to laser-induced grating, and thus the conductivity is associated with charge diffusion. The results show that the total refractive-index change causing the self-diffraction is only slightly smaller for the Mg-doped samples than for undoped LiNbO3 while the conductivity is 1 order of magnitude greater for the Mg-doped samples.

Anisotropic self-diffraction in KNbO3

Anisotropic diffraction and self-diffraction processes in KNbO3 crystals are investigated utilizing the large elementr51 of the electro-optic tensor. Geometrical conditions, polarization changes, phase conjugation, phase doubling and the dynamics of hologram recording are studied theoretically and experimentally. Anisotropic diffraction with equal or different frequencies for recording and reading permits the determination of photo- and dark conductivity. Further material properties are estimated on the assumption that the charge transport is governed by diffusion effects.

Selfdiffraction and phase conjugation of laser beams in electrooptic crystals

Different types of selfdiffraction (isotropic and anisotropic) are described theoretically. It is shown that anisotropic selfdiffraction differs substantially from the isotropic one: for instance in nonpolar crystals the direction of the energy exchange between two beams depends on the wave polarisation. Several new types of two-wave and four-wave schemes of phase conjugation are discussed. [Russian Text Ignored].

Anisotropic scattering in photorefractive crystals

A well-defined ring of anisotropically scattered light is observed when a linearly polarized laser beam is incident upon a birefringent photorefractive crystal such as BaTiO3, LiNbO3, and LiTaO3. An analysis is presented that accurately predicts the cone angle, polarization, and the location of the discontinuities in these rings. Unlike the photovoltaic model proposed recently by others, the analysis presented herein is based on the standard photorefractive theory and is independent of the photovoltaic activity of the crystal. The analysis also illustrates the strict phase matching and electro-optic tensor symmetry constraints that must be satisfied in order to observe beam coupling and normal and anisotropic self-diffraction. Preliminary experimental results are presented for BaTiO3 and LiNbO3 and are found to be in excellent agreement with standard photorefractive theory.

Anisotropic selfdiffraction in BaTiO3

Anisotropic selfdiffraction in BaTiO3 crystals utilizing the large electrooptic coefficientr42 is described. In the absence of an external electric field the generated space charge field is determined by diffusion processes. The theory is in agreement with the experimental results. The angles between extraordinary and ordinary beams, the intensity and time dependence of transmitted and diffracted beams, and phase conjugation effects are measured and evaluated.