B. I. Sturman

Photorefractive nonlinearity of periodically poled ferroelectrics

We study theoretically the dependence of the photorefractive response of a periodically poled ferroelectric on the spatial frequency of light fringes, on the period of the domain inversion, and on its mark-to-space ratio. The photovoltaic effect, the drift of photoelectrons under an applied field, and their diffusion are considered as charge-transport mechanisms. Strong suppression of the photorefractive properties at low spatial frequencies (reduction of optical damage) together with retention of these properties in a region of short-fringe spacing are shown. We also found that the periodicity of the domain structure can produce a new kind of photorefractive parametric wave coupling. This coupling is characterized by a large gain factor for the waves propagating at angles that depend on the domain-inversion period. Finally, we discuss promising photorefractive experiments in periodically poled lithium niobate.

Grating translation technique for vectorial beam coupling and its applications to linear signal detection

We develop the theory of vectorial beam coupling in cubic photorefractive crystals to describe the effect of fast phase modulation on output intensities and polarizations. Special emphasis is given to new features of the grating translation technique compared with its scalar variant. We show, in particular, that a strong nonlocal ac response in crystals of the sillenite family can be effectively used for the linear detection of fast signals. Theoretical results are supported by polarization ac experiments with Bi12TiO20 crystals.

Threshold for pattern formation in a medium with a local photorefractive response

Threshold equations for the instability of counterpropagating waves against spontaneous initiation of small-angle light patterns are analyzed for a medium with a local photorefractive response and various boundary conditions. These equations take into account all actual contributions to the reflection phase gratings. The form of the threshold equation is directly related to the spatial symmetry of the problem. We study the dependence of the threshold thickness of the crystal and the angle of light emission on experimentally controllable parameters and discuss the prospects for experimental studies of pattern formation in LiNbO3 crystals.

Two kinetic regimes for high-temperature photorefractive phenomena in LiNbO 3

We propose a physical model to explain peculiarities of photorefractive recording and dark decay detected in LiNbO3 crystals within temperature ranges below and above 200 °C. Distinctive features of our description are proximity of the activation energies for protons and thermally excited electrons and their competitive contributions to the charge transport.

Mechanism of self‐organized light‐induced scattering in periodically poled lithium niobate

It is shown that the photorefractive grating produced by a pair of plane waves in periodically poled lithium niobate includes an additional set of spatial harmonics related to the periodic domain structure. This results in new schemes for photorefractive wave coupling. Using the modified phase matching conditions and the concept of optical oscillation we accurately describe the position of the diffraction peaks and explain the main characteristics of self‐organized photoinduced scattering reported recently.

Photorefractive ac response beyond the low-contrast limit

We show that a photorefractive crystal, placed in an ac field and exposed to nonuniform light, exhibits singularities of the induced space charge and discontinuities of the corresponding space-charge field. For a symmetric beam, the singularity appears at the intensity maximum when the light contrast exceeds a certain (rather low) threshold value. Also, we analyze a diffraction model to understand the effect of the singular ac response on the propagation of a Gaussian light beam.