V. P. Kamenov

Optimum orientation of volume phase gratings in sillenite crystals: is it always [111]?

We study the simultaneous influence of optical activity, piezoelectric effect, and elasto-optic effect on two-wave mixing (TWM) under diffusion recording in photorefractive Bi12TiO20 and Bi12SiO20 crystals and find numerically the maximum of the TWM gain as a function of the orientation of the grating vector. Contrary to widespread belief, the grating orientation K∥[111] is the optimum orientation only if optical activity is negligibly small. Nonzero optical activity results in a strong dependence of the optimum grating orientation on the crystal thickness. The strongest deviation of the optimum from the [111] direction is achieved for ϱd=180°, where ϱ is the rotatory power and d is the crystal thickness. Our theory explains well prior results for crystals of moderate thickness and predicts new effects for thick (e.g., fiberlike) crystals.

Giant momentary readout produced by switching electric fields during two-wave mixing in sillenites

We show theoretically and experimentally that switching an applied square-wave field produces strong and short pulses of the outgoing signal during two-wave mixing in sillenite crystals. These pulses originate from the strong effect of the field on the optical eigenmodes and can be used in new optical schemes based on time-separated recording and readout processes.

Resonant vectorial wave coupling in cubic photorefractive crystals

We present a theory of resonant photorefractive wave coupling in cubic photorefractive crystals that are in general optically active. This theory includes the resonance enhancement of the photorefractive response in a constant applied electric field, the influence of photoelasticity, and the spatial inhomogeneity of the light intensity. In a unified manner, it allows one to describe the polarization and energy properties of two-wave coupling for the optical configurations relevant to experiment. Applications of the theory are given to photorefractive crystals of the sillenite family.

Attractors and auto-oscillations for feedback controlled photorefractive beam coupling

Abstract We investigate the physics of a novel nonlinear system, feedback controlled photorefractive beam coupling. Inertia of the electronic feedback is found to be an element crucial for permanent operation of this system. Theoretically and experimentally we have found a wealth of periodic and quasi-periodic regimes for observable characteristics of the feedback controlled wave coupling. A good qualitative agreement between theory and experiment is obtained for LiNbO 3 crystals.

Diffusion recording in photorefractive sillenite crystals: an analytical approach for engineering purposes

Simple formulae for the two-wave mixing (TWM) gain and diffraction efficiency obtained in the approximation of weak coupling and strong optical activity allow us to tune the experimental setup for interferometric applications. We prove that two invariant parameters, trace and determinant of the coupling tensor, are sufficient to optimize the experimental setup. Both practically important crystal cuts, (110) and (111), can be treated in a unified manner. Fundamental TWM properties (90°-jumps of the optimum polarization, apparent doubling of the local maxima of the diffraction efficiency in comparison with the gain, drastic changes between regimes of small and large polarization rotation, the crucial role of elastooptic properties) are systematized. The guidelines for the design of an optimum experimental setup for interferometric applications including anisotropic self-diffraction using sillenite crystals are presented. Quantitative agreement with previous experimental data is demonstrated.

Instability of the resonance excitation of space-charge waves in sillenite crystals

We analyze analytically and numerically the mechanism for modulational instability of the resonance excitation of a space-charge field by a moving light pattern in a photorefractive sillenite crystal to explain the results of recent experiments with Bi12SiO20 crystals.

Rigorous three-dimensional theory of subharmonic instability in sillenites

We propose a theory of the instability of the space-charge field induced in a semiconductor by the movement of light fringes against subharmonic generation. A crucial element of this theory is taking into account three-dimensional perturbations and higher spatial harmonics of the space-charge field. It is shown that, irrespective of fringe contrast and velocity, the strongest instability corresponds to the excitation of subharmonics that are not split in the transverse direction. The theory is applied to experimental data on subharmonic generation in sillenites.

Formation of moving light domains during photorefractive feedback-controlled beam coupling

Abstract We investigate the spatial structure of dynamic index and light gratings which arise during feedback-controlled photorefractive beam coupling with ultimate diffraction parameters. It is shown that the interference light fringes are split inside the crystal into two domains moving in the opposite directions; at the domain’s boundary they experience periodic breaking. The index grating generated by this light pattern consists of only one quasi-stationary domain. The found phenomenon is interpreted in terms of the theory of fast phase modulation.

Theoretical study of feedback-controlled photorefractive beam-coupling dynamics

Theoretically we investigate the operation of a novel nonlinear system, feedback controlled photorefractive beam coupling. It is shown that the feedback conditions used earlier ((pi) /2 phase shift between the diffracted and transmitted beam components) are satisfactory only during a relatively short initial stage of development. We have generalized these conditions by taking into account the inertia inherent any real feedback loop. The inertial feedback conditions ensure the permanent operation of the nonlinear system and lead to a variety of periodic and quasi-periodic regimes. We investigate the distinctive features of these regimes and transitions between them for moderately thick crystals.

Elastic contributions to electro-optics

In this talk I shall show you how the electro-optic effect is modified by elasticity and also give a few applications from the field of volume-holography in photo-refractive crystals. I shall also comment on a striking similarity between the electro-optic effect owing to elasticity and the magnetostatic field owing to a distribution of electric currents.