J. Limeres

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.

Nonlinear generation of higher-order combinational gratings during sequential recording in LiNbO 3

The observation of diffraction spots from strong higher-order combinational gratings during sequential recording of two photorefractive holograms in a LiNbO3 crystal is reported. To the best of our knowledge, this is the first time that combinational photorefractive gratings of third and fourth order have been detected. The influence of the parameters of both intentionally recorded gratings on the amplitude of second-order combinational components (K1+K2 and K1-K2) has been investigated. We have found that the strength of these gratings essentially increases with the amplitude of the first grating recorded and with the modulation of the second grating recorded. However, the combinational gratings behave differently from the second-harmonic gratings in some respects. The results can be qualitatively explained in terms of the nonlinearities of band transport equations.

Nonlinear mixing of spatial frequencies in photorefractive thermal fixing of holograms in LiNbO3

Abstract The nonlinear combinations of gratings appearing in fixed multiplexed configurations during the recording as well as during the fixing of holograms in LiNbO 3 has been investigated. We have obtained significant differences in comparison with the previously studied case of non-fixed holograms. Moreover, we have found that the relative strength of the combinational gratings depends on the particular experimental procedure used for thermal fixing. The first observation of fixed combinational gratings is also reported obtaining diffraction efficiencies of ∼0.01% for the sum and difference gratings. Our results should be relevant for applications involving fixed multiplexed holograms.

Nonlinear grating interactions in multibeam photorefractive recording: theoretical investigation

The nonlinear interactions between gratings generated during multibeam photorefractive recording with one reference and N object beams have been investigated theoretically. It is shown that nonlinear cross talk between gratings, which is well known in three-beam recording, persists and even increases for the practical relevant case in which the number of object beams N is large. The magnitude of the cross talk depends on the particular grating, and it is significant for a range of intensities commonly used in many multibeam applications. Finally, it is shown that for large N(N>5) the nonlinear interactions strongly suppress most gratings, whereas specific gratings can be selectively amplified.

Influence of multigrating operation on the generation of phase-conjugate beams by four-wave mixing

A numerical simulation for studying the kinetics of phase-conjugate beams generated by multigrating four-wave mixing has been developed. It has been applied to investigate the four-wave mixing process in BaTiO3 by use of realistic coupling coefficients. The role of the distinct gratings has been analyzed. Depending on the experimental conditions, constructive as well as destructive interference of the different contributions was obtained. Moreover, because of grating competition effects, π-phase changes in the phase-conjugate beam can occur during the kinetics. For large values of the coupling strength and specific regions of the physical parameters, unstable four-wave mixing dynamics were obtained. The analysis of the results provides some criteria for predicting the phase conjugator’s behavior in multigrating conditions.