Photorefractive Ferroelectric Crystal Research Articles

Turbulent Transitions in Optical Wave Propagation.

We report the direct observation of the onset of turbulence in propagating one-dimensional optical waves. The transition occurs as the disordered hosting material passes from being linear to one with extreme nonlinearity. As the response grows, increased wave interaction causes a modulational unstable quasihomogeneous flow to be superseded by a chaotic and spatially incoherent one. Statistical analysis of high-resolution wave behavior in the turbulent regime unveils the emergence of concomitant rogue waves. The transition, observed in a photorefractive ferroelectric crystal, introduces a new and rich experimental setting for the study of optical wave turbulence and information transport in conditions dominated by large fluctuations and extreme nonlinearity.

Spatial Rogue Waves in Photorefractive Ferroelectrics.

Rogue waves are observed as light propagates in the extreme nonlinear regime that occurs when a photorefractive ferroelectric crystal is undergoing a structural phase transition. The transmitted spatial light distribution contains bright localized spots of anomalously large intensity that follow a signature long-tail statistics that disappears as the nonlinearity is weakened. The isolated wave events form as out-of-equilibrium response and disorder enhance the Kerr-saturated nonlinearity at the critical point. Self-similarity associable to the individual observed filaments and numerical simulations of the generalized nonlinear Schrödinger equation suggests that dynamics of soliton fusions and scale invariance can microscopically play an important role in the observed rogue intensities and statistics.

Localized switching in photorefractive ferroelectrics induced by spatially inhomogeneous electric fields

We examine theoretically the stability of 180° domain patterns that may form inside photorefractive ferroelectric crystals when an optically induced spatially modulated electric field is present. By analyzing the total free energy of a ferroelectric crystal subjected to an applied field and with free charges contained within, we find under what conditions (magnitude of the applied field, amplitude of the optically induced electric field, and domain-wall energy density) the spontaneous polarization of the crystal tends to switch throughout the whole crystal and under which only partial switching occurs.

Polarization reversal of the wavefront of light beams in photorefractive crystals

A theoretical study is made of the possibility of reversal of the wavefront of a light beam in respect of the phase and polarization by degenerate four-wave interactions in photorefractive ferroelectric crystals. It is shown that the polarizations of the signal and reversed waves can be conjugate only under certain conditions which must be satisfied by the intensity, phase, and polarization of the pump beams, and also by the orientation of the optic axis of a crystal. Specific situations when these conditions are satisfied are considered in the case of photorefractive ferroelectric crystals of the 3m and 4mm symmetries.

Diffraction of light by phase holograms in photorefractive ferroelectric crystals

The kinematic approximation is used in an investigation of the theoretical solution of the problem of diffraction of arbitrarily polarized light waves by static volume phase holograms in uniaxial crystals. The diffusion, drift in a field, and photogalvanic mechanisms of photorefraction are allowed for and no restrictions are imposed on the orientation of the optic axis of a crystal. Several special cases are considered for crystals of the symmetry classes 3m and 4mm when measurements of the intensity of the diffracted radiation can be used to estimate the contribution of the various mechanisms to the process of formation of a hologram and the conditions are established for the reconstruction of the polarization of an arbitrarily polarized object wave.