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The photorefractive (PR) properties of high performance PR organic monolithic glasses containing dicyanomethylenedihydrofuran (DCDHF) chromophores are reviewed. Two-beam coupling net gain coefficients of ~200-400 cm-1 were obtained at the wavelengths of 676 nm and 830 nm. Beam self-focusing and defocusing observed in DCDHF glasses are discussed. Beam guiding in the optically induced waveguide is demonstrated.

We present a detailed investigation of a photorefractive surface plasmon polariton system capable of coupling energy between two predefined surface plasmon modes with efficiencies up to 25%. We have investigated the dependence of the diffraction efficiency on the energy, the initial and final wavevectors of the surface plasmon modes, and the cell parameters. We have also developed numerical simulations of the system based upon the defect-free Q-tensor approach and rigorous diffraction theory, which fit the experimental data very well and have allowed us to develop a good theoretical understanding of the performance of these cells. On the basis of the experimental results and theory we discuss the prospects that a hybrid liquid crystal photorefractive system could lead to photorefractive gain for surface plasmon polaritons.

Summary form only given. The space-charge gratings and the conduction properties of photorefractive (PR) polymer films are investigated by taking advantage of the non-steady-state photo-ElectroMotive Force (or photo-EMF) effect. When a hologram is recorded under non-stationary conditions, e.g. by a vibrating interference pattern, interaction between the quasi-stationary space-charge field grating and the vibrating distribution of mobile charge carriers leads to a periodic electric current (photo-EMF current J/sup /spl Omega//) with the same frequency /spl Omega/ as the vibration of the interference pattern. Furthermore, if an external DC field is applied, a second harmonic photo-EMF current (J/sup 2/spl Omega//) is observed.

We optically characterize a photorefractive SBN:60 crystal. We measure absorption coefficient, two beam coupling gain coefficient and diffraction efficiency, which are found to strongly dependent on the beam intensity. These provide strong evidence that shallow traps play an important role on grating formation. By using a transmission configuration recording and a Bragg-matched diode laser we show that electric field tunability is feasible by observing the changes on the spectra of the diffracted diode laser.

Sn2P2S6 is a fast responding photorefractive ferroelectric material with very attractive properties for applications in the near infrared. It exhibits high electro-optic coefficients up to r T 111 = 174pm/V at 633nm and room temperature, large transparency range in the infrared (530–8000 nm), and a high photorefractive sensitivity. We show that modifying the growth conditions and doping with Te can efficiently improve the photorefractive properties of Sn2P2S6. Photorefractive two-beam coupling gain at 860 nm increases from about 2 cm-1 in conventional

Nonlinearity of the photorefractive response is studied experimentally and theoretically upon two-beam interaction of light waves in a bismuth silicate crystal placed in an external meander electric field. The experimental data are shown to be in good agreement with a model, taking into account the influence of the second harmonic of the space-charge field on a photorefractive grating. The concentration of acceptors in a crystal and a product of the mobility of charge carriers by their recombination time are estimated from a comparison of the experimental and calculated data.

A significant improvement of the ring-cavity self-pumped phase conjugation response time in the near-infrared cw regime with a photorefractive brown Sn2P2S6 crystal is reported. Brown Sn2P2S6 is grown by the vapor-transport technique with SnI2 as the transport agent. With our Sn2P2S6 samples response times below 50 ms and phase-conjugate reflectivities of 25% can be achieved at a wavelength of 780 nm with a moderate light intensity of 1 W/cm2. We show that the measured reflectivity represents the limit given by the transmission of the ring-cavity arrangement. Reaching this limit is possible because of the large two-wave mixing gain of 18 cm-1 measured in this crystal.

We present the characterization of highly photorefractive Er3+/Yb3+-doped 75SiO2-25GeO2 planar waveguides, single mode at 1550 nm, deposited by radio-frequency-magnetron-sputtering (RFMS) technique. Details of the deposition process are reported. The material presents an intense absorption band (alpha approximately 10;3/10;4 cm;-1) in the UV region. Irradiations by a KrF excimer laser source at lambda = 248 nm have produced large positive (up to 310-3) refractive index changes, without the need of particular sensitization procedures. Direct measurements of UV photo-induced volume densification demonstrates that glass compaction accounts for large part of the refractive index change. Highly efficient photo-induced phase gratings have thus been fabricated in the waveguide.

We demonstrated an InGaAs-GaAs photorefractive MQW device with quantum confined Stark effect (QCSE) for the first time. The maximum diffraction efficiency is 2x10/sup -4/. This value is 100 times smaller than the expected one. This disagreement indicates the effect of the lateral transport.

We propose a mathematical model for the movement in absorbing materials of photorefractive holograms under feedback constraints. We use this model to analyze the speed of a fringe-locked running hologram in photorefractive sillenite crystals that usually exhibit a strong absorption effect. Fringe-locked experiments permit us to compute the quantum efficiency for the photogeneration of charge carriers in photorefractive crystals if the effect of bulk absorption and the effective value of the externally applied field are adequately taken into consideration. A Bi12TiO20 sample was measured with the 532-nm laser wavelength, and a quantum efficiency of Φ=0.37 was obtained. Disregarding absorption leads to large errors in Φ.

The high-performance photorefractive polymer hybrid liquid crystal structures are investigated in detail by use of optical tow-wave mixing technique. In such structures an amplification of laser light can be realized by two-beam coupling mechanism. Photorefractive properties of the structures rely on the spatial light induced charge carrier density modulation in thin film of photoconducting polymer. The spatially modulated space-charge field induces efficient reorientations of molecules of adjacent to polymeric layer nematic liquid crystal forming, in this way, the refractive index grating. Efficient energy transfer between the incident and the higher-order diffracted beams has been observed in dynamic self-diffraction process on thin phase gratings at oblique light incidence. The phase shift between the light intensity pattern the light intensity pattern and the refractive index modulation grating, responsible for the energy exchange, can be controlled by the applied electric field enabling reversal of direction of energy flow. Energy transfer and diffraction efficiency are found to exhibit different response characteristics with fringe spacing, voltage, cell parameters and light modulation-depth. The net exponential gain coefficient reported for the structures amounted to (Gamma) approximately equals 2600 cm$_-1) and was obtained at driving voltages of the order of 1 V/micrometers .

We show theoretically and experimentally that the photorefractive nonlinearity possesses a big potential for manipulating light pulses, including their slowing down, long term storage and release on demand. Particular examples are considered.

A theoretical model considering total internal reflections of fanned beams from the side crystal surfaces and their coupling with the pump beam is proposed. The interaction of these beams results in the light intensity redistribution and in the generation of the photorefractive surface wave. An experimental observation of the light intensity self-concentration near the surface of a thin photorefractive Bi12TiO20 crystal is reported. It results in an acceleration of the photorefractive energy exchange process.

Summary form only given.Summary from only given. Photorefractive multiple quantum wells (MQWs) have been applied to the ultrasound detection, the depth-resolved image recognition through turbid media, and so on. The fabrication of photorefractive MQW devices at 1064 nm and its applications to proposed measurement systems are very attractive and interesting. Furthermore, the realization of these devices may create the new area of applications of photorefractive MQWs. Here, we report on the fabrication of photorefractive InGaAs-GaAs MQWs and its performance at the wavelength of 1064 nm.

We show that Talbot effect can be used to enhance the two-wave mixing gain of two photorefractive liquid crystal light-valves in cascade and that self-pumped phase conjugation can be obtained in an optical feedback scheme.

In recent years ferroelectric materials with their large electrooptic coefficients have found new optical applications in the field of phase conjugate optics, image processing and dynamic holography. Some of these applications are based on the photoinduced refractive index changes or photorefractive effect which are due to the linear electro-optic effect driven by photoinduced space-charge fields. In this paper we give a review of recent nonlinear optical experiments with photorefractive ferroelectrics.

We present a model which can be used to predict the effects of doping and oxidation-reduction treatment on the photorefractive behavior of BaTiO3, crysta1s.1 The densities of photorefractive centers are calculated from a thermodynamic point defect model. These centers may exist in multiple charge states; the occupation of each the temperature and oxygen partial pressure of processing and dopant concentration. The beam coupling gain and response time are calculated using the electron-hole model, where the photorefractive donor and acceptor densities are derived from the defect model.

The photorefractive properties of a nominally pure single crystal of BaTiO3 were altered by treating the crystal at 650°C in oxygen at different partial pressures. Treatment altered the effective density of photorefractive charge carriers in the crystal and could convert an inactive crystal into an active one. Treatment at low oxygen pressure (reduction) decreased the temperature of the tetragonal-to-cubic phase transition of the crystal and also decreased the measured optical band gap, implying that oxygen vacancies had been introduced into the bulk crystal. These oxygen vacancies are associated with negative photorefractive charge donors. Either hole transport or electron transport dominated, depending on whether the partial pressure of oxygen was greater than or less than ½ atm during treatment. The competing roles of electrons and holes are discussed.

We present a model that provides a means for understanding the effects of crystal growth and processing conditions on the photorefractive properties of BaTiO3. The densities of photorefractive centers are calculated from a thermodynamic point defect model. This model allows for the existence of transition-metal dopants in multiple valence states and for the incorporation of more than one species with levels in the band gap. Beam-coupling gain and response time are calculated as a function of temperature and oxygen partial pressure of treatment for various dopant types and concentrations. The predicted behavior is compared with existing experimental data on BaTiO3 crystals, and implications for improving the photorefractive performance are discussed.