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Photorefractive materials are capable of reversibly changing their index of refraction upon illumination. That property allows them to dynamically record holograms, which is a key function for developing an updateable holographic 3D display. The transition from inorganic photorefractive crystals to organic polymers meant that large display screens could be made. However, one essential figure of merit that needed to be worked out first was the sensitivity of the material that enables to record bright images in a short amount of time. In this review article, we describe how polymer engineering was able to overcome the problem of the material sensitivity. We highlight the importance of understanding the energy levels of the different species in order to optimize the efficiency and recording speed. We then discuss different photorefractive compounds and the reason for their particular figures of merit. Finally, we consider the technical choices taken to obtain an updateable 3D display using photorefractive polymer. By leveraging the unique properties of this holographic recording material, full color holograms were demonstrated, as well as refreshing rate of 100 hogels/second.

The photorefractive effect presents a periodical change of the refractive index of an optical environment under the influence of a coherent light. An interesting phenomenon which occurs at this effect is optical phase conjugation (PC). Photorefractive oscillators, that is photorefractive mirrors present important decides in photorefractive optics and their function is based on photorefractive effect. In these oscillators, a phase-conjugated light beam occurs. The basic characteristics of photorefractive oscillators, such as reflectivity, the existance of the oscillation threshold and the threshold of the coupling strength are explained by the so-called grating-action method. This is analysed on a ring oscillator, semilinear mirror and linear mirror.

The dynamic refractive-index-change behavior of the light-induced process in an Mn:Fe:KTN crystal illuminated by a focused light sheet can be observed experimentally by digital holographic interferometry. By numerically retrieving a series of sequential phase maps from recording digital holograms, the spatial and temporal evolution of the light-induced refractive-index-change distribution inside the material is visualized in situ and monitored in a quantitative and in full field way. With this technique, the effect of recording parameters, such as writing laser power and polarization, bias voltage, temperature, and writing time, on the Mn:Fe:KTN crystal in the photorefractive effect can be explored. Therefore, optimized recording parameters will be achieved according to the dynamic behavior. The method provides an access to explore the evolution of the photorefractive (PR) effect of electrooptic crystal under various situations.

In organic optical semiconductors, it is rather challenging to achieve precise control of photoconductivity and charge trapping, which determines the device performance. This paper reports on enhanced photorefractive response rate through control of the photoconductivity and trapping rate in organic triphenylamine-based photorefractive materials by means of bulk state tuning. The bulk state in organic triphenylamine-based photorefractive composites was controlled through a rapid cooling process from various melting temperatures during sample fabrication. The photoconductivity and trapping rate were determined from photocurrent measurements. Fabrication at lower melting temperatures enhanced the trapping rate for deep traps, whereas it reduced the trapping rate for shallow traps. As a result, a faster photorefractive response was obtained.

In this paper, we review recent progress of research on the photorefractive effect of ferroelectric liquid crystals. The photorefractive effect is a phenomenon that forms a dynamic hologram in a material. The interference of two laser beams in a photorefractive material establishes a refractive index grating. This phenomenon is applicable to a wide range of devices related to diffraction optics including 3D displays, optical amplification, optical tomography, novelty filters, and phase conjugate wave generators. Ferroelectric liquid crystals are considered as a candidate for practical photorefractive materials. A refractive index grating formation time of 8–10 ms and a large gain coefficient are easily obtained in photorefractive ferroelectric liquid crystals.

Organic photorefractive (PR) materials have been studied during the last quarter-century, and they have recently received much attention due to their updatable features that allow them to be used in dynamic holographic devices. However, understanding bulk trap sites that drive the PR effect (by inducing a space-charge field) remains a critical issue. In general, the trap site behavior can be controlled from the energetic point of view; however, bulk devices contain not only the energy trap sites but also structural neutral ones, which decrease the carrier mobility. Organic PR devices are bulk optoelectronics devices, and the investigation of their trap tuning mechanism is still ongoing. In this thesis, carrier transport and trapping properties of the PR materials (represented by triphenylamine-based polymers) with induced space-charge fields are investigated. The effects of plasticizers and wavelengths of interference beams on the PR performance of the resulting holographic devices are studied via photoconductivity measurements. In order to solve a critical challenge of trap tuning, a modified fabrication technique is proposed, which enhances the photoconductivity of the PR materials by suppressing shallow traps. The trap site properties are controlled by studying bulk dipolar molecules with a photoemission yield spectroscopy in air technique, which provides the distribution of both the transport and trap sites. Finally, dynamic holographic images were produced by using organic PR composite films.

Comparative studies are made of the photorefractive scattering of light in nonlinear single crystals of lithium niobate with congruent compositions (LiNbO3) doped with "photorefractive" Cu [0.015 mass %] and "nonphotorefractive" Zn [0.5 mass %] cations. For the first time it is found that single crystals doped with "photorefractive" and "nonphotorefractive" cations have different indicatrices for photorefractive light scattering. The aperture angle for photorefractive scattering reaches its steady state value more rapidly with high laser powers than with low. However, at high powers laser induced heating of the crystal is greater, and this leads to a narrowing of the scattering indicatrix. It is also found that photorefractive scattering in these single crystals depends on the region of the boule from which a sample has been cut. This indicates that there is a nonuniform distribution over the boule of the imperfections with localized electrons which determine the magnitude of the photorefractive effect.

Photorefractive active block copolymers were successfully synthesized via an atom transfer radical polymerization of acrylate containing liquid crystalline moiety and hole transporting carbazole moiety. Resulting copolymers were characterized by gel permeation chromatography, NMR, and DSC. Copolymers afforded the transparent films showing birefringent nature. Photorefractive characteristics of copolymers with 2 wt% of trinitro- fluorenone as a photosensitizer were investigated by four wave mixing and two-beam coupling methods with a He-Ne laser. For the block copolymer, higher diffraction efficiency and larger coupling gain were observed compared with the corresponding statistical random copolymer.

This paper reviews our recent work on the photorefractive effect in liquid crystalline materials. The photorefractive effect is defined as the optical modulation of the refractive index of a medium as a result of various processes. The interference of two laser beams in a photorefractive material establishes a refractive index grating. This phenomenon enables the creation of different types of photonic applications. Recently, the development of organic photorefractive materials has been attracting great interest. Liquid crystalline materials are a strong candidate for practical photorefractive materials and application. In this paper, the photorefractivity of liquid crystalline polymers and ferroelectric liquid crystals is described.

Optically controlled spatial light modulator was demonstrated as application of photorefractive polymeric material. Since photorefractive composite based on carbazole-substituted polysiloxane matrix (PSX-Cz) has an advantages of stability in phase separation, compared to poly(N-vinyl carbazole) based composite, we can dope almost all kinds of chromophore with the PSX-Cz to prepare a photorefractive composite. Here a chromophore 2-[3-[( E )-2-(piperidino)-1-ethenyl]-5,5-dimethyl-2-cyclohexenyliden] malononitrile (P-IP-DC), with large dipole moment and large polarizability anisotropy was adopted into a photorefractive sample, which showed a high diffraction efficiency of 85 % at an external field of 28 V/μm. Using this photorefractive composite, incoherent image imposed in Xe-lamp light was converted into coherent image in He-Ne laser light by the optically controlled spatial light modulator.

Photorefractive polymers have been extensively studied for over two decades and have found applications in holographic displays and optical image processing. The complexity of these materials arises from multiple charge contributions, for example, leading to the formation of competing photorefractive gratings. It has been recently shown that in a photorefractive polymer at relatively moderate applied electric fields the primary charge carriers (holes) establish an initial grating, followed by a subsequent competing grating (electrons) resulting in a decreased two-beam coupling and diffraction efficiencies. In this paper, it is shown that with relatively large sustainable bias fields, the two-beam coupling efficiency is enhanced owing to a decreased electron contribution. These results also explain the cause of dielectric breakdown experienced under large bias fields. Our conclusions are supported by self-pumped transient two-beam coupling and photocurrent measurements as a function of applied bias fields at different wavelengths.

We report on the photoelectric conversion at a non-photovoltaic photorefractive material sandwiched between transparent conductive electrodes. Its behavior is based on the light-induced Schottky effect. Its nature and performance was clearly established by wavelength-resolved photoconductivity. OCIS codes: Photoconductivity (040.5150); Photorefractive Materials (160.5320); Optoelectronics (230.0250)

Photorefractive materials are being widely investigated for applications in holographic data storage1. Inhomogeneous illumination of these materials with an optical interference pattern redistributes charge, builds up internal electric fields and so changes the refractive index. Subsequent homogeneous illumination results in light diffraction and reconstructs the information encoded in the original interference pattern. A range of inorganic and organic photorefractive materials are known2, in which thousands of holograms of high fidelity can be efficiently stored, reconstructed and erased. But there remains a problem with volatility: the read-out process usually erases the stored information and amplifies the scattered light. Several techniques for ‘fixing’ holograms have been developed3,4,5,6, but they have practical disadvantages and only laboratory demonstrators have been built7,8,9,10. Here we describe a resolution to the problem of volatility that should lead to the realization of a more practical system. We use crystals of lithium niobate — available both in large size and with excellent homogeneity — that have been doped with two different deep electron traps (iron and manganese). Illumination of the crystals with incoherent ultraviolet light during the recording process permits the storage of data (a red-light interference pattern) that can be subsequently read, in the absence of ultraviolet light, without erasure. Our crystals show up to 32 per cent diffraction efficiency, rapid optical erasure of the stored data is possible using ultraviolet light, and light scattering is effectively prevented.

We present the time-of-flight measurements of hole mobility in a photorefractive polymer composite as a function of temperature and applied electric field. The analysis shows that the temperature dependence of the low-field mobility is in apparent disagreement with the predictions of the Gaussian disorder model and also with polaron models.

Time-reversed ultrasonically encoded (TRUE) optical focusing focuses light beyond one transport mean free path by phase-conjugating the ultrasonically tagged light. However, in previous works, only a small portion of the tagged light was phase-conjugated by using a photorefractive Bi_(12)SiO_(20) crystal, due to its small active area (1x1 cm^2). In this work, we report high-efficiency TRUE focusing using a large-area photorefractive polymer (5x5 cm^2), which demonstrated ~40 times increase in focused energy. Further, we imaged absorbers embedded in a turbid sample of thickness of ~12 transport mean free paths.

We investigate experimentally and numerically a novel method of modifying photorefractive waveguides in a lithium niobate crystal by a guided beam. The guided beam with a strong optical power can change the refractive index of the photorefractive waveguide because of the photorefractive effect. The modification of waveguide structure can be utilized for optical dynamic interconnection. Changes of optical characteristics of a probe beam caused by a modification beam are investigated. Experimental results show that the transmitted power or the peak intensity of the probe beam decreases exponentially as a function of total exposure energy of the modification beam. We also numerically analyze the refractive index change caused by the modification beam in the photorefractive waveguide. The numerical results show good agreement with the experimental results.

A photorefractive system is one which is simultaneously photoconductive and electrooptic. Diffraction gratings or holograms can be produced in a photorefractive material by the photogeneration, drift or diffusion and subsequent trapping of mobile charges. The grating is produced by the internal space charge field set-up by these charges which, via the electrooptic effect, produces an index of refraction grating. Until 1990 all photorefractive systems were inorganic crystals such as LiNbO,, BaTiO,, B,,SiO,, InP:Fe, GaAs, or multiple quantum well materials. In 1990, the first observation of the photorefractive effect in an organic material, a carefully grown, doped molecular crystal was described. This was followed in short time by the discovery of photorefractive polymers. The early photorefractive systems, polymeric and crystalline, were inefficient compared to inorganic systems but in recent years the efficiency and sensitivity of photorefractive polymers have become equal to inorganic crystals. This paper describes the origins of the photorefractive effect and the design, synthesis and characterization of photorefractive polymers. In addition an orientational enhancement of the photorefractive diffraction efficiency is discussed. This orientational enhancement does not occur in crystalline systems, since it relies on the ability of the optically nonlinear chromophores to be aligned not only by an externally applied field, but also by the sinusoidally varying space charge field produced during photorefractive grating formation.

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We report on the experimental evidence of the light intensity dependence of the Debye screening length l(s) in undoped photorefractive titanosillenite crystals (Bi12TiO20) by measuring the holographic gain and diffraction efficiency in a two-wave mixing experiment under 532 nm wavelength laser light. Debye length shows saturation at high values of the light intensity. Results are in agreement with the theoretical development Aberto

PHOTOREFRACTIVE materials are of considerable interest for the development of all-optical devices1. The photoref ractive effect appears in materials that exhibit an electric-field-dependent refractive index and that are photosensitive, such that the spatial distribution of photogenerated charge carriers is modified on irradiation with light. The diffraction pattern formed by the interference of two coherent light beams within such a material generates a non-uniform internal electric field that in turn modulates the refractive index. The resulting refractive-index pattern forms a grating that can diffract light and thereby give rise to two-beam coupling, whereby one of the writing beams gains energy at the expense of the other—a property that can be exploited in photonic devices. Although the best photorefractive materials currently available are inorganic crystals such as LiNbO3, there is considerable interest in the development of photorefractive polymers2–8, owing to their structural flexibility, ease of processing and lower cost. We describe here a polymer composite with excellent photorefractive properties. We have achieved a diffraction efficiency approaching 100% and a net two-beam coupling gain of more than 200 cm–1, making these polymeric materials suitable for immediate application in areas such as dynamic holographic storage and optical information processing1.

We report the simultaneous diffraction cancellation for beams of different wavelengths in out-of-equilibrium dipolar glass. The effect is supported by the photorefractive diffusive nonlinearity and scale-free optics, and can find application in imaging and microscopy. © 2011 Optical Society of America.

Permanent photorefractive gratings with considerable refractive index modulations (~3×10–4) were written in silica optical fibers doped with very low levels of SnO2(~0.15 mol %) using ultraviolet (UV) laser radiation at 248 nm. The photoinduced refractive index change does not show any sign of saturation even for long exposure times (i.e., total fluence >20 kJ/cm2). A comparison with GeO2:SiO2 fibers shows that under similar UV intensities saturation takes place for shorter exposure time and comparable refractive index changes are obtainable for GeO2 concentrations ~10 mol %.

We model the optical properties of L3 photonic crystal nano-cavities as a function of the photonic crystal membrane refractive index n using a guided mode expansion method. Band structure calculations revealed that a TE-like full band-gap exists for materials of refractive index as low as 1.6. The Q-factor of such cavities showed a super-linear increase with refractive index. By adjusting the relative position of the cavity side holes, the Q-factor was optimised as a function of the photonic crystal membrane refractive index n over the range 1.6 to 3.4. Q-factors in the range 3000-8000 were predicted from absorption free materials in the visible range with refractive index between 2.45 and 2.8.

The investigation of the light-induced changes of refractive index in a LiNbO(3): Fe sample in case of strip-like illumination is presented in the contribution. The changes of the refractive index are visualized by interferograms of the sample obtained for various orientation of the illuminated strip and various polarization of the light used during interferogram creation. The investigation shows that character of the dependences of the refractive index on the coordinate perpendicular to the illuminated strip is different for different strip orientation. It indicates the possibility that for different orientation of gradient of the illumination the different mechanisms are responsible for changes of the refractive index.

The properties of anisotropic diffraction of light by volume holographic grating in birefringent photorefractive crystals are discussed. This diffraction takes place when the refractive index for diffracted light is different from the refractive index for incident light. It is found that in some special geometry of wavevector diagram the diffraction becomes less sensitive to the wavelength mismatch of Bragg condition. The wavelength range may extent in several times the range of ordinary isotropic diffraction on the grating of the same spacing and thickness. Theoretical explanation of this phenomena and experimental results of widerange diffraction in BaTiO3 photorefractive crystal are also presented.

International audience; By using soluble fullerene derivative [60]PCBM, we improved photorefractive efficiency in polymer-liquid crystal composites in comparison to previous works on similar materials. We show the effect of polymer network results in resolution and bandwidth improvements compared to pure liquid crystals. This is explained by the introduction of a charge trapping mechanism, providing a memory effect for the composite. Based on this effect, we propose an approach for designing composites with higher grating efficiency and resolution.

An interferometric Mach-Zehnder technique very recently developed has been applied to measure photorefractive index changes in different types of z-cut proton-exchanged planar waveguides in LiNbO(3). These measurements are complemented by determining the intensitythreshold for the onset of optical damage with a standard single-beam setup. In the intensity region just below the threshold-intensity obtained in the single-beam experiment the refractive index change is found to saturate at values around1x10(-4). Furthermore, we measure the dark conductivities of proton-exchanged waveguides by monitoring the decay of the light-induced index changes. Via the time constant of the decay we obtain dark conductivities of the order of about 5x10(-16) Omega (-1) cm (-1), that are negligible compared with the photoconductivity within the light intensity range used. The results of the measurements compare well with the predictions of a recent work, that uses a two-center model to explain the optical damage.

The photorefractive behaviour of a novel type of optical waveguides fabricated in LiNbO3 by swift heavy ion irradiation is investigated. First, the electro-optic coefficient r 33 of these guides that is crucial in the photorefractive effect is measured. Second, two complementary aspects of the photorefractive response are studied: (i) recording and light-induced and dark erasure of holographic gratings; (ii) optical beam degradation in single-beam configuration. The main photorefractive parameters, recording and erasing time constants, maximum refractive-index change and optical damage thresholds are determined. © 2009 Springer-Verlag., This work was supported by the Ministerio de Educación y Ciencia (MEC) under grants MAT2005-06359-C03 and MAT2008-06794-C03. J. Villarroel acknowledges the financial support of the MEC through his FPI fellowship.

We report the first observation of the photorefractive effect in a polymeric material, the electro-optic polymer bisphenol-A-diglycidylether 4-nitro-1,2-phenylenediamine made photoconductive by doping with the hole-transport agent diethylamino-benzaldehyde diphenylhydrazone. The gratings formed exhibit dynamic writing and erasure, strong electric-field dependence, polarization anisotropy, and estimated space-charge fields up to 26 kV/cm at an applied field of 126 kV/cm. Application of similar concepts should provide a broad new class of easily fabricated photorefractive materials.

Binary information in the form of a 256 x 256 pixel array has been stored holographically within a polymeric photorefractive composite of 130-mum thickness. Devices used consisted of 55-wt. % organic chromophore 1-(2?-ethylhexyloxy)-2, 5-dimethyl-4-(4?nitrophenylazo) benzene and up to 11.2-wt. % 2, 4, 7-trinitro-9-fluorenone (TNF) dispersed within a poly(N-vinyl carbazole) matrix. In a degenerate four-wave mixing arrangement, the refractive-index modulation and speed were 10(-3) and 200 ms, respectively. The high TNF concentration leads to short digital hologram recording times of 2 s without detriment in optical quality. Although not yet optimized, a figure of merit, M#, for holographic storage in this composite has been measured to be 0.017, and this is estimated to reach 0.18 in a revised experimental geometry.

A cw-probe Z-scan technique was employed to measure the photoinduced index change in a photorefractive SBN:60 crystal. For this experiment a three-detector data-acquisition system was used to account for temporal changes in the laser. The effects of various beam parameters such as intensity, polarization, and wavelength were studied. A theoretical simulation of the Z scan based on a band-transport model of photorefractive-index variation was also developed. This model provides reasonable agreement with the experimental results.

It is demonstrated that Er doping increases the photorefractive effect in LiTaO3. Raman and fluorescence spectra are used to establish that the upconverted green emission of Er3+ clusters acts as a gating source, significantly increasing the two-photon photorefractive effect of a monochromatic red or near-infrared pump source.

Infrared imaging materials with high speed and dynamic range are required for a variety of imaging and diagnostic techniques. We present an organic photorefractive glass that shows high diffraction efficiencies of as great as 40% with 25-mum-thick samples and fast response times of 4.3 ms under irradiation at 790 nm. Furthermore, the intensity dependence and field dependence of the grating decay are investigated.

A photorefractive incoherent-to-coherent optical converter (PICOC) is demonstrated; conversion is accomplished by anisotropic self-diffraction in BaTiO(3). The setup of the PICOC is easy, and only two writing beams are required. The diffraction efficiency reaches 50%, and the resolution is 22 line pairs (lp)/mm in a typical-size crystal. Further, the resolution reaches 40 lp/mm when a BaTiO(3):Rh crystal of thickness 1.2 mm is used, and the diffraction efficiency is as high as 51%. The resolution of the PICOC can be increased effectively by reduction of the crystal thickness with no penalty for low diffraction efficiency.

This paper reviews our recent work on the photorefractive effect of ferroelectric liquid crystals (FLCs). The photorefractive effect is defined as the optical modulation of the refractive index of a medium as a result of a variety of processes. The interference of two laser beams in a photorefractive material establishes a refractive index grating. This phenomenon enables the creation of different types of photonic applications. FLCs exhibit fast electric field response, and the orientation of the molecular axis of FLCs changes its direction according to the change in direction of the spontaneous polarization (Ps). When two laser beams interfere in a photoconductive FLC, an orientational grating is formed. The mechanism of the formation of the grating is based on the response of the Ps to the photoinduced internal electric field. The time of formation of the refractive index grating is significantly shorter in FLC materials.

Numerous interaction geometries have been developed for photorefractive materials that rely on amplification of light via the two-beam coupling effect. One of the most elegant and simple configurations is a unidirectional ring resonator, which consists of a photorefractive crystal placed in a ring cavity and pumped by an external beam. If the two-beam coupling gain is above threshold, the resonating beam will build up from the amplification of scattered light. We present results on the most crucial parameters for the effective build-up of power in the resonating beam the wavelength of the pump beam, and the type of photorefractive material. The resonating beam accumulates energy from successive amplification in a photorefractive material until saturation sets in but also loses energy from absorption and other losses such as Fresnel reflections from the crystal and imperfect mirrors. We have performed intensity-dependent modelling of the resonator's power conversion factor. The power conversion factor is defined as the ratio of the resonating beam intensity to the intensity of the external pump beam. The figure below shows the dependence of this factor on absorption coefficient for different values of coupling coefficient Gamma.

A photorefractive oscillator. mutually pumped by three wavelengths is presented in various configurations and competition effects demonstrated. The theoretical model used to simulate the behaviour of the oscillation beams is in good agreement with experimental data.

We show theoretically that the group velocity of light can be slowed down by means of phase coupling in the photorefractive two-wave mixing process. It is shown that the group velocity of light propagating in a photorefractive material could be significantly reduced because of a steep variation of the phase-coupling coefficient with respect to the angular frequency difference between two coupling beams in a two-wave mixing process. The results for the case of a photorefractive Bi12SiO20 crystal are presented and discussed in detail.

By means of a comparative study, we identify a specific physical mechanism that leads to circular-symmetric two-dimensional photorefractive solitons, and determine the conditions for their observation. For a given photorefractive crystal, this allows the control of the transition from an elliptical soliton-supporting regime to a round soliton-supporting one. This indicates a basic recipe to generate electro-optic devices in three-dimensional crystals compatible with single-mode fiber.

The photorefractive properties of Ge-doped glasses are routinely exploited for the production of Bragg gratings in optical fibres. Today, the most common fabrication procedure relies on the phase-mask technique, which allows to produce (through UV irradiation) a periodical refractive index variation in Ge-doped fibre cores. The same methodology can be applied to integrated optical components in photorefractive glass planar substrates. If rare earth ions (such as erbium and ytterbium) are included in the glass matrix, both active and photorefractive properties can be combined in the same material. This fact allows for the possibility of realizing complex integrated optical components, such as Bragg-reflection lasers and amplifiers. In this work, a numerical analysis of a waveguide Bragg reflector is presented based on a homemade modelling technique.

The decay of holograms stored in photorefractive polymer composites based on poly(N-vinyl-carbazole) with and without extrinsic deep traps is investigated. The photorefractive phase shift is identified as one of the key parameters determining the dark decay dynamics. This has important implications for all kinds of photorefractive imaging applications including holographic data storage. A trade off will be required between accepting a certain degree of hologram distortion due to two-beam coupling on the one hand and achieving high hologram stability during idle periods in the dark with the external field applied on the other.

Detailed analysis of the relationship between the experimental geometry and the holographic contrast in photorefractive polymers is important for applications, such as angle multiplexing in holographic data storage. In this paper the field dependent photogeneration efficiency is introduced into the complete reorientational model to provide a full account of the electric field and geometrical dependence of the index contrast. The interaction of a local grating and the photorefractive grating is also considered. A simplification for acute angles between writing beams is described. Experimental verification by use of four-wave mixing and transmission ellipsometry reveals an excellent agreement between theory and measurement.

The photorefractive response of several dye-doped nematic liquid crystal samples is studied experimentally. Particular attention is given to the observation and modeling of the multiexponential dynamics of the photorefractive grating, and of the photocurrent. Both involve at least two different mechanisms with largely different time constants. These phenomena occur on time scales on the order of seconds, for applied voltages about 1 V, and light intensities as low as milliwatts/cm(2). (C) 2002 American Institute of Physics. Content may be divided into these groups: --Supplementary matter on instrumentation and site setting --Continuous time series data of drip and precipitation rate, water and air temperature, and specific conductance --Discrete and composite geochemical samples

The purpose of this paper is to find the polarizations and spatial orientations of the two interacting counterpropagating coherent light waves which ensure the largest beam coupling in monoclinic photorefractive crystal. The results of calculations are presented that are verified experimentally with Sn₂P₂S₆.

This article analyzes nonlinear light propagation in semiconductors with bipolar conductivity and nonlinear transport of electrons. We show how the competition between electron and hole conductivity can influence light propagation, leading to the self-bending effect of optical beam trajectory, which depending on the value of trap compensation coefficient may be stationary or transient.

We report the observation of steady-state two-dimensional photorefractive self-trapping and screening spatial soliton formation in a sample of potassium–lithium–tantalate–niobate in the centrosymmetric paraelectric phase.

We have characterized a two-wave mixing adaptive interferometer based on dc-biased photorefractive CdTe:Ge crystal at 1.06 and 1.55 μm. Excellent performance is shown at both wavelengths by demonstration of high sensitivity for measurement of small displacements and high cutoff frequency at low intensity. We have achieved a considerable reduction of the undesired low-frequency response using controlled heating of the crystal, which ensures depopulation of corresponding traps. The experimental data are used for measurement of the real and imaginary parts of the coupling constant, as well as the dielectric relaxation time of the crystal and the mobility-lifetime product of the free charge carriers.

We study the influence of a transient dark current on the buildup dynamics of photorefractive index gratings, which are excited right after the onset of a pulsed voltage, by using low glass-transition temperature photorefractive polymers under a heat-assisted condition. We conclude that the development of photorefractive index gratings is majorly controlled by changes in the transient dark current, through the suppression of a saturated photo-induced space-charge electric field. We also show that this influence can be estimated reasonably well by a simple analysis of the measured transient current traces.