bluuebunny/crossref_metadata_2025 huggingface dataset:
Holographic Implementation Of 2-D Perfect Shuffles Based on a One-Copy Algorithm
Authors: Wang J.M. , Cheng L. , Sawchuk A.A.
Published: February 2023

There are several ways of performing optical perfect shuffles. One method is to use classical optical components such as lens arrays [1][2], a combination of lenses and prisms [3] and Fresnel mirrors [4], etc.. The shift operations required by the perfect shuffle can be realized by proper spatial arrangement of these components. Another method is to use Fourier optics: by placing an optical spatial filter with a cosine transmittance function in the Fourier transform (F.T.) plane, an optical 4-f system can accomplish the perfect shuffle permutation [5]. In this paper, we propose an alternative method which uses a hologram to perform the 2-D perfect shuffles. It is based on a light efficient one-copy algorithm.
Recent advances in communication network theory
Authors: Leighton F. T.
Published: February 2023

In this survey of recent advances in communication network design and algorithms for message routing, emphasis is placed on a novel class of randomly-connected networks known as multibutterflies.
Low threshold optical bistability in bulk GaAs etalons
Authors: Acklin B. , Bagnoud C. , Dupertuis M.A.
Published: February 2023

A promising device for parallel optical computing is the nonlinear Fabry-Perot (NLFP), where a nonlinear refractive index change related to optical carrier excitation in a semiconductor layer is amplified inside a Fabry-Perot (FP) cavity. Research activity in this field [1,2,3] has evolved towards all-epitaxially grown structures; the use of alloy and multiple quantum well material; thermally stable operation; and recently, towards biased and array operation.
An Optical Time Slot Interchanger
Authors: Erkkila Tracy H.
Published: February 2023

This paper describes the implementation of an optical time slot interchanger using LiNBO3 directional couplers. A time slot interchanger (TSI) is a time-domain switch which arranges time slots, or packets of digital information which have been serially multiplexed onto a common carrier. By rearranging the order of these slots in time, packets can be routed to their desired destination. TSI's have applications in telecommunication networks, and an optical implementation provides a good match to existing and future hardware in this field. An optical TSI can also be used as a non-blocking, high speed interconnection network in a multiprocessor environment, or in a local area network (LAN).
All Optical, High Contrast Switching in an Asymmetric Fabry-Perot Etalon
Authors: Heffernan J.F. , Moloney M.H. , Hegarty J. , Roberts J.S. , Whitehead M.
Published: February 2023

The concept of an absorption modulated Asymmetric Fabry-Perot(AFP) etalon has been reported and demonstrated by several authors1–3, all based on electro-optic modulation. These devices show promise as suitable candidates for optical switches and optical processing elements required for optical computing. They exhibit the high contrast ratios necessary but have a rather high insertion loss and contacting these devices in large scale arrays may prove to be a difficult problem. We report switching in an Asymmetric Fabry-Perot etalon which relies on optical modulation only. The device exhibits a high contrast ratio with low input power and at higher powers has almost no associated insertion loss.
The Growth of BaTiO3 Crystals and The Research on Crystal Defects of Them by Electro-microscope Technique
Authors: Xing Wu , Yong Zhu , Daofang Zhang , Cuiying Yang
Published: February 2023

BaTiO3 crystals are very useful as an excellent photorefractive materials. But the growth of BaTiO3 crystals is very difficult due to some special chemical and physical properties of them. The BaTiO3 crystals in good optical quality have been grown successfully by Top Seed Solution Growth (TSSG) technique but the crystal defects happened easyly due to the unsuitable in the crystal growth conditions even just a little. The temperature distribution near the crystal growth front, the suitable seeding temperature, stabilyty of the growth interface and so on are very important to keep the crystal growth well and in good optical quality. All of these main conditions for growing of crystals were researched detailly in our experiments and discussed detailly in this paper.
Electron Irradiation Damage to KNbO3
Authors: Hodgson E.R. , Zaldo C. , López F. Agulló
Published: February 2023

The optical absorption induced by electron irradiation in KNbO3 has been investigated with a Van de Graaf accelerator. A well defined threshold energy of 0.35 MeV has been found to induce colouring. A broad band roughly peaked at 450 nm is formed above threshold. The observed coloration has been related to the displacement of oxygen atoms.
Absorption Modulation Under Hologram Formation in Photorefractive Materials
Authors: Knyazkov A.V. , Lobanov M.N.
Published: February 2023

It has been found, that some photorefractive materials, such as GaAs and BaTiO3, exhibit an intensity dependence in the absorption coefficient and the presense of absorption component of hologram grating [1,2]. We have shown in our previous paper [3], that hologram formation in photorefractive media has an amplitude - - phase character due to spatial redistribution of absorptive centres. For analysis we have used a band model with one type of photoactive centres.
Photochromic Effect in Bi12SiO20 Crystals
Authors: Panchenko T.V. , Kudzin A.Yu.
Published: February 2023

The study of photochromic effect in pure and doped Bi12SiO20 (BSO) crystals is useful both as for science and so for application. In articles [1-3] the photochromic effect in BSO doped with Cr and Mn has been studied. However the mechanism of the light induced charge transfer and nature of impurities are not clear. In this study the results of optical spectra investigation for BSO crystals doped with Al,Ga, Cr,Mn and Fe ions and crystals with compositions slightly deviated from ideal stoichiometric proportion are presented.
Examination of Electric Fields in Ferroelectrics by Impact Ionization
Authors: Rost Timothy A. , Rabson Thomas A.
Published: February 2023

The space charge fields present in ferroelectric thin films are examined with impact ionization. The possibility of using this technique as a probe to aid in the understanding of the bulk photovoltaic effect is discussed.
Optical Memory Effect based on Deep Level Filling and Depletion in Semi-Insulating Materials
Authors: Pugnet M. , Collet J. , Sirvin R. , Nardo L.
Published: February 2023

The absorption of a radiation pulse propagating through a semiconductor is described by non-linear time dependent photon transport equations, which account for the effect of the radiation on the deep level electron population and conversely (photon energy is lower than the band gap). We consider optical pulse widths shorter than the propagation time in the sample. In such a case, the pulse trailing edge interacts with an electron population which has been modified by its leading part. Equations are solved in closed form for an arbitrary input pulse and an arbitrary initial electron distribution on deep levels. The solution is discussed for lorentzian pulses. The energy transmission ratio T = Etrans/Einc is calculated versus the optical capture cross-sections and the initial electron distribution; the case of two delayed pulses at different wavelengths is especially discussed. In optical data processing the first pulse is the writing pulse and the second is the reading one. The optical storage time dependence versus the semiconductor parameters is discussed. This model is used to analyze the transmission of picosecond pulses through GaAs:Cr-O samples at room temperature.
Net Gain in Photorefractive InP:Fe at λ = 1.32 µm Without an Applied Field
Authors: Strait J. , Reed J. D.
Published: February 2023

Gain is one of the most attractive aspects of the photorefractive effect. Phase conjugators and other applications become possible when photorefractive gain exceeds absorption losses. Semiconductors, such as InP and GaAs, have small electro-optic coefficients, so it has been necessary to apply electric fields of several kV/cm to realize large gains. In InP:Fe, a gain of 3 cm-1 first was reported with a 10 kV/cm AC applied field1 and later a gain of 4 cm-1 was obtained with an 8 kV/cm DC field.2 Recently gains as large as 6 cm-1 have been reported for an 8 kV/cm DC field.3 While it is not possible to have such large gains in InP:Fe without an applied field, the high voltages required are not practical for device applications.
Non linear absorption in BSO, BGO crystals induced by picosecond pulses
Authors: Sylla M. , Rouède D. , Chevallier R. , Xuan N. P. , Rivoire G.
Published: February 2023

High value of non linear absorption is observed in BSO crystals excited by 25 picosecond pulses. The time evolution suggests the existence of a large free carrier absorption and an absorbing level near the conduction band.
Dynamic Photorefractive Interconnects With Analog Weights
Authors: Marrakchi A. , Hubbard W. M. , Patel J. S.
Published: February 2023

Multiplexing of holographic gratings has potential application in the implementation of optical interconnects betweeen individual processing elements (or neurons) of two distinct planes in a neural network. Therefore, the capability of continuously modifying a given strength (or weight) without affecting the others is a critical issue. In this paper, we analyze grating erasure in photorefractive materials for the realization of interconnects with analog weights. The effects of both intensity and phase modulation of the writing beams on the diffraction efficiency and on the response time are considered. The phase modulation analysis includes the double-exposure and time-average techniques. Some insight on the limiting factors to the storage capacity which ultimately determines the number of possible interconnections are also given. Finally, preliminary results of an interconnect system that utilizes fast liquid crystal modulators are described.
Photorefraction Without the Electrooptic Effect
Authors: Pierce R.M. , Cudney R.S. , Bacher G.D. , Feinberg Jack
Published: February 2023

Photorefractive crystals can couple optical beams in more than one way. In the usual photorefractive effect, light redistributes charge between empty and full trapping sites in the crystal. The electric field of the charge then alters the refractive index of the crystal by the electrooptic effect. However, the trapping sites themselves produce a variation in the local polarizability of the crystal. If the incident intensity pattern is periodic in space, then the resulting periodic redistribution of trapping sites will form a grating that can scatter light, even if the electrooptic effect is zero in the crystal. This "trap" grating is always 90° out of phase with the electrooptic grating, due to the spatial derivative in Gauss's law.
Self-pulsating and moving fringe-patterns in the outputs of a mutually-pumped BaTiO3
Authors: Ye Peixian , Wang Dadi , Zhang Zhiguo
Published: February 2023

Recently, much attention has been paid on a new type of phase conjugation in BaTiO3 in which two mutually incoherent beams pump each other to generate the respective phase-conjugate reflections. Since the double phase-conjugate mirror was discovered1, several mutually-pumped phase-conjugators have been proposed and demonstrated.2-4 We report here on a configuration for mutually-pumping in which both the PC reflections are seen to undergo regular self-pulsating and moving fringes appear both on the far-field patterns of the reflected outputs.
Sequential power transfer between stripes of a laser diode array via photorefractive two beam coupling in BaTiO3
Authors: MacCormack S. , Eason R.W.
Published: February 2023

The combination of the output of a semiconductor laser array into a high power, diffraction limited output is currently the subject of great interest, but is technically difficult since any system considered must exhibit a dynamic response to the phase variations of the individual stripes of the laser array. Photorefractive materials, because of their ability to cope with rapid phase variations, and in addition, display large nonlinear effects at the milli-Watt power levels associated with individual stripes of a diode laser array, provide an ideal medium in which to perform coupling techniques.
High-Resolution Optical Novelty Filter Using Photorefractive GaAs And High-Speed Nematic Liquid Crystal Phase Modulator
Authors: Liu Duncan T. H. , Cheng Li-Jen , Wu Shin-Tson
Published: February 2023

Recently, optical novelty filters [1] have attracted much attention because of their potential applications in motion detection and optical tracking. Most optical novelty filters reported to date use BaTiO3 crystal as the needed nonlinear medium. In a previous report [2], we have shown that, owing to the shorter response time of GaAs, the output resolution of a GaAs based optical novelty filter is potentially much higher than that of a BaTiO3 based optical novelty filter. However, a relatively high-speed spatial phase modulator is needed for such an implementation. As a result, the usual nematic liquid crystal (NLC) modulators used in other implementations of optical novelty filter would respond too slow for the current implementation. Nevertheless, recently, the speed of NLC modulator has been greatly improved by various methods. For example, using the transient nematic effect, a frame time of less than 50 μs have been demonstrated [3]. Such a frame time is more than adequate for the current implementation. In this paper, we report the result of an investigation on the potential of building a high-resolution optical novelty filter using photorefractive GaAs and high-speed nematic liquid crystal phase modulator.
The Multiplexed Storage of Permanent and Real-Time Holograms in Photorefractive BSO for Use in Image Processing and Spatial Light Modulation
Authors: Clapham S.L. , Eason R.W. , Vainos N.A.
Published: February 2023

In this paper we present a technique for storing holograms in crystals of bismuth silicon oxide (BSO) that combines reversible photochromic effects with the more usual real-time photorefractive characteristics. Photochromic effects have been observed before in these sillenite crystals [1] but have generally been considered as a problem rather than as a possible mechanism for holographic storage. As the normal photorefractive (PR) behaviour is unaffected, however, simultaneous spatial multiplexing of both photorefractive (real-time) and photochromic (permanent) holograms is possible in the same crystal volume.
Self Pumped Phase Conjugation and Optical Light Oscillation in Fe Doped KNbO3
Authors: Medrano C. , Ingold M , Günter P.
Published: February 2023

In recent years, self-pumped phase conjugation and self-induced photorefractive light oscillation have been reported, using different photorefractive materials. The main photorefractive materials used in these experiments are BaTiO3 and Bi12SiO20. In ferroelectric BaTiO3 the high electro-optic coefficients give rise to large reflectivities. In photoconductive and paraelectric Bi12SiO20 phase shifting techniques lead to enhanced self-diffracted intensities and phase conjugate reflectivities. KNbO3 is such a material which in addition to its high photorefractive sensitivity3 and large beam coupling gain4, has been shown to become highly photoconductive if prepared properly, leading to optimized response speed5 down to 100 μs. In a degenerate four wave mixing configuration, maximum phase conjugate reflectivities up to 25% with an applied electric field have been observed several years ago6. In a previous paper7 and for the first time, the possibility of using KNbO3 crystals for self-induced optical resonators has been reported. Both an unidirectional ring and a linear resonator configurations were realized and coherent light oscillations observed. Build up time constants of milliseconds were reported when an undoped reduced KNbO3 crystal was employed. However the measured phase conjugate reflectivity for these configurations were very small. Later on self-pumped phase conjugation in KNbO3 has been reported at 124°C8. In this paper we report on self-pumped phase conjugation experiments, performed with an iron doped KNbO3 crystal at room temperature in both a linear and a passive ring resonator configuration. We also report on self-pumped phase conjugation in a configuration requiring no external optical elements. Results deriving from degenerate four-wave mixing are also presented.
On the Buildup and Decay of Photorefractive Wave Mixing Processes
Authors: Horowitz Moshe , Fischer Baruch
Published: February 2023

Photorefractive media have been used for many novel applications in image processing. One interesting use is the novelty filter which is an all optical processor based on the response of two wave mixing (2-WM) or four wave mixing (4-WM) [1,2]. It is obvious that the temporal dymnamics of the wave mixing process is essential to understand such processes. However, since the overall photorefractive dynamics, including the wave mixing part, is described by complicated nonlinear partial differential equations, it is hard to obtain a general solution. The study has been largely limited to steady state behavior and the response of the photorefractive material only, without taking into account the dynamics of the wave coupling effects.
Spatial Solitons in Photorefractive Media
Authors: Segev Mordechai , Saa'r Amir , Yariv Amnon
Published: February 2023

Light solitons in space (spatial solitons) have been under an intensive theoretical and experimental research in the last three decades. The solitons evolve from nonlinear changes in the refractive index of the material, due to the light intensity distribution. When the modulation of the index confines the light beam in such a way that diffraction is compensated for exactly, the beam becomes self-trapped, and is called a spatial soliton. The nonlinear effects, which are responsible to soliton formation, are in general Kerr-like effects, causing local index changes proportional to the local light power. The index changes needed for spatial solitons require high power densities, and often exceed 1MWatt/cm2 (see ref.[1]).
Resolution limit of photorefractive spatial light modulators
Authors: Amrhein P. , Günter P.
Published: February 2023

The experimental set-up of our photorefractive incoherent to coherent converter 1 is shown in figure 1. With two interfering Ar-ion-laser beams (λ=514.5 nm) we write a phase hologram into a photorefractive KNbO3 crystal. Using anisotropic Bragg diffraction 2 we choose the direction of the diffracted beam (λ=632.8 nm) perpendicular to the crystal surface. The input image is projected into the crystal plate anti-parallel to the diffracted beam. A short wavelength transmitting dichroitic beam splitter is used to separate the incoherent light from the diffracted beam. This set-up shows highest resolution 3.
Phase-coded hologram multiplexing for high capacity optical data storage
Authors: Denz C. , Pauliat G. , Roosen G. , Tschudi T.
Published: February 2023

Reconfigurable volume holograms are important for a wide range of multiple data storage applications, including optical interconnection systems, image processing and neural network models. Therefore, there has been much previous work on multiplexing techniques to obtain a large number of stored images which can be recalled independently. But even the most promising of these multiplexing techniques, angular multiplexing using the selectivity of the Bragg-condition, revealed to be limited primarily because of cross-correlation noise. Moreover, mechanically changing the incident angle of the reference beam1,2 requires a high reliability in the positioning and is therefore inherently slow. To overcome these problems, an intensity spatial light modulator can be used to define the various angular multiplexed incident directions3.
Applied Electric Field Effect on Photorefractive GaAs
Authors: Liu Duncan T. H. , Cheng Li-Jen , Kim Jae-Hoon
Published: February 2023

Compound semiconductors such as GaAs are known to be very fast photorefractive materials. However, due to their relatively small electro-optic coefficient, their diffraction efficiency is much smaller than that of most oxide materials such as BaTiO3. Even so, easily detectable signal with fairly good signal to noise ratio can be usually achieved in a GaAs based application without the aid of an external electric field due to the cross-polarization coupling1 capability of GaAs and the high sensitivity of modern video cameras. For example, in a recently demonstrated real-time optical image correlator2, the correlation output was normally strong enough to saturate the vidicon camera used. On the other hand, in some applications such as the ring oscillator, the double phase conjugate mirror, and the self-pumped phase conjugator, a sufficiently large net two-beam coupling gain is needed. In compound semiconductors, net gain had been achieved by applied electric field techniques. However, in general, these techniques have two side effects, namely the Schottky-barrier effect3 and the low-frequency current oscillation effect4. Depending on the particular requirement of an application, these effects may or may not be a problem. But, they are not desired in general. In this paper, we report the results of a study on the electrode material dependence of the Schottky-barrier effect in the undoped GaAs crystal. In particular, the widely-used silver-paste electrodes are compared with thermally-evaporated alloy electrodes.
Photorefractive properties and alternating electric field gain enhancement of vanadium-doped cadmium telluride and related compounds
Authors: Ziari Mehrdad , Steier William H. , Klein Marvin B. , Trivedi Sudhir
Published: February 2023

Recent studies of the photorefractive response of CdTe have demonstrated it to be a highly sensitive material with a broad near infrared sensitivity extending to beyond 1.5 μm[1,2]. Desirable parameters, such as large electrooptic coefficient, small dielectric constant, large carrier mobility and availability in semi-insulating form, makes CdTe a potential material of choice for many applications[3]. This study focuses on photorefractive characterization of Bridgeman grown crystals with the goal of providing the information that can lead to the optimization of key photorefractive parameters. We have observed gain and broad sensitivity (1-1.5 μm) in vanadium doped CdTe and Cd0.96Zn0.4Te samples. Mixed alloys such as CdZnTe and CdMnTe allow band gap engineering such that the sensitivity range could be tuned toward the visible and be matched to the wavelength of interest. An applied alternating (AC) field gain enhancement technique is used to demonstrate net gain which is a prerequisite for coherent amplification and self-pumped phase conjugation.
Syncnrotron X-ray Diffraction Imaging of Photorefractive Crystals
Authors: Fogarty Gerard , Cronin-Golomb Mark
Published: February 2023

Signal processing in photorefractive crystals is complicated by photore­fractive amplified scattering (fanning). The scattering centers responsible for seeding the fanning noise may be presumed to be traceable to crystal lattice irregularities. These defects have not yet been examined in any great detail, and the relative importance of various specific imperfections and the role they play in the crystal optics are not known. An understanding of these defects should lead to improvement in signal processing through growth of more satisfactory photorefractive crystals. We have set out to address these problems through direct, in situ observation of photorefractive crystals and their gratings in barium titanate by high resolution monochromatic synchrotron x-ray diffraction imaging. The results that we report here indicate the nature of the principal limiting imperfections and demonstrate the feasability of direct observation of photorefractive gratings and scattering centers.
New Thresholding Device using a Double Phase Conjugate Mirror with Phase Conjugate Feedback
Authors: Tayebati Parviz , Dornash Lawrence H.
Published: February 2023

We present a new thresholding device consisting of a double phase conjugate mirror (DPCM) combined with a phase conjugate mirror resulting in superior thresholding characteristics compared to that of a DPCM alone.
Breaking of the electrooptic and dielectric tensor symmetries by space charge electric fields
Authors: Pauliat G. , Mathey P. , Roosen G.
Published: February 2023

The space charge electric field associated with a photorefractive grating generates deformations (through piezoelectricity) which in turn, modify both the electrooptic and dielectric constants. These modifications are of importance and must be taken into account1. For instance, in BaTiO3 samples the dielectric constant ϵ11, determined using spatially uniform applied electric fields, varies by a factor of two between clamped and unclamped crystals. Hereafter, we demonstrate that these differences are even more important for space charge electric fields because these non uniform fields induce strain components which are not produced by uniform fields. Therefore, the effective electrooptic coefficient can be different from zero in a configuration in which both the clamped and unclamped coefficients for uniform fields vanish.
Photoinduced Charge Transport in Optical Damage Resistant LiNbO3:Me (Me = Mg, Zn)
Authors: Volk T.R. , Ivanov M.A. , Shchapov F. Ya. , Rubinina N.M.
Published: February 2023

Photoinduced charge transport in LiNbO3 is defined by presence of a Fe-like impurity, Fe2+ being the donor, Fe3+-the acceptor of electrons1. Two level scheme gives the linear dependence of photoconductivity (that is of inverse response 2 times of photorefraction) on the light intensity2.
Hologram Recording in GaAs through EL2 Intracentre Absorption
Authors: Khromov Andrei L. , Petrov Michael P.
Published: February 2023

Deep donor centre, referred to as EL2, is the dominant deep level in melt-grown GaAs crystals. Photoionization of EL2, the subsequent space charge redistribution, and refractive index modulation through the electrooptic effect are responsible for what we call below the photorefractive (PR) gratings observed in GaAs semi-insulating crystals, see e.g. [1]. EL2 centre is also distinguished by a number of specific features including the existence of the excited metastable state EL2* of the same charge. EL2 ⇒ EL2* transitions take place tinder light excitation with photon energy hν between 1.0 and 1.3 eV. At low temperatures T≈100 K the corresponding cross section σ* and lifetime τ* are sufficiently large (σ* ≈ 10−17sm2, τ* ≈ 10 s according to [2]) and hence the metastable state EL2 strongly affects the absorption and photocurrent spectrums, some photoelectrical properties of the material, etc. [3,4]. Nevertheless, the probable influence of EL2 ⇒ EL2* transitions on the properties of GaAs crystals as a reversible holographic medium is still in question.
Charge Transport in High-Resistivity Photorefractive Crystals (Bi12SiO20, ZnSe, GaAs)
Authors: Ilinskii A. V.
Published: February 2023

The paper reviews our studies[1−7] concerned of photoinduced charge dynamics and electric field evolution in the case of external field screening. The experimental methods providing possibility of electric field distribution direct measurements are considered. It is found that there are two different regimes of electric field screening which depend on experimental conditions (kind of crystal, temperature): narrowing of major cariers depletion region and stratification effect (numerous space charge layers of alternating sign) with increasing charge density - regime 1 and the slow broadening of single layer with constant charge density may occur in bulk of a sample - regime 2.These regimes were experimentally investigated in Bi12SiO20, ZnSe and GaAs crystals. A theoretical description is given of a sufficiently general charge transfer model involving the photogeneration of free carriers, their drift and trapping throughout the depth of the material.
Application of Beam Fanning in a Photorefractive BaTiO3 Crystal: Measurement of Light Scattering at Zero Degrees by a Single Glass Fiber
Authors: Padmabandu G. G. , Oh Choonghoon , Fry Edward S.
Published: February 2023

The photorefractive effect in BaTiO3 has been the subject of extensive research in recent years. Because of very large electro-optic coefficients, BaTiO3 has become a unique candidate for a variety of nonlinear optical devices which operate at very low light intensities. Most of these devices use energy transfer between coherent optical beams that interfere inside the crystal while some devices use the extinction of a single beam through beam fanning1-3.
Low-Frequency Noise and Photoinduced Scattering in Photorefractive Crystals
Authors: Sturman B.I.
Published: February 2023

Photoinduced scattering (PS) is inherent in a varying degree in any photorefractive crystal. The origin of the PS is quite clear: this is an amplification of the weak seed scattering. A number of papers, for example [1-3], deal with a description of the effect. The pump and scattered waves supposed usually to have the same frequency. In the framework of that approach, a steady-state PS may only be caused by the nonlocal photorefractive response (i.e. by shifted gratings). However, in many cases experiments show the steady-state PS to be abnormaly large and this can not be accounted for by the nonlocal response. LiNbO3:Pe crystals, where the local response (i.e. unshifted gratings) exceed in value the nonlocal one by 101-102 times, can be pointed out as an example.
Spectroscopy of Light Sensitive Defect/Impurity Centers in Photorefractive BaTiO3
Authors: Schwartz Robert N. , Wechsler Barry A. , McFarlane Ross A.
Published: February 2023

Control and optimization of the behavior of photorefractive crystals requires first, a thorough understanding of the nature (charge state, local symmetry, and electronic structure) of the defects/impurities present in these materials, and of their interaction with light.1,2,3 Toward this end, we have carried out electron paramagnetic resonance (EPR), photo-EPR, and optical absorption measurements on a variety of BaTiO3 samples doped with transition metal ions. These crystals were grown by top-seeded solution growth from a melt with an excess of TiO2.
Determination of the Effective Trap Density of Ta:KNbO3 and BaTiO3 at 823 nm
Authors: Clement A.E. , Gilbreath G.C. , Fugera S.N.
Published: February 2023

There is considerable interest in finding a viable photorefractive coupler which operates in the near-infrared regime for use with laser diodes and laser diode arrays. A potential application for such a combination may be in laser spacecraft communications where a photorefractive coupler may serve as both an energy coupler and an adaptive optical component.[1] The III-V materials are undesirable components for a spacecraft environment due to the requirement to place large fields across the crystals and because the net gains in these materials remain quite low. Therefore, the study and potential development of existing diffusion-driven media toward increased infrared response may be useful. Two such materials of interest are BaTiO3 and poled KNbO3. The diffusion-driven response of the latter is of specific interest in this work.
Picosecond Nonlinear Optical Responses in Photorefractive Crystals
Authors: Liu H. , Reeves R.J. , Powell R.C.
Published: February 2023

Picosecond-pulse laser excitation was used to establish and probe refractive index gratings in KNbO3, KTaO3, and mixed crystals of KTa1-xNbxO3. The purpose of this work was first to identify the physical processes contributing to fast nonlinear optical responses in these samples, and second to determine how these processes evolve with time into the space-charge field photorefractive effect observed with continuous wave excitation. The techniques of pulse-probe degenerate four-wave mixing and nondegenerate four-wave mixing with a continuous wave probe laser were both employed to obtain information about the photorefractive processes that take place after fast pulse excitation. The measurements were made as a function of laser fluence, crossing angle of the write beams, sample orientation with respect to the grating wavevector, polarization directions of the write and probe beams, and write beam wavelength. Mixed crystals with the niobium concentration parameter x varying from 0 to 1.0 were investigated along with KNbO3 samples containing a variety of dopant ions.
Analytic and Numeric Results on Subharmonics in BSO
Authors: Bledowski A. , Sturman B. , Otten J. , Ringhofer K. H.
Published: February 2023

Recently, experiments with Bi12SiO20 (BSO) initiated by Mallick et al.[1] and continued by the Oxford group[2, 3, 4, 5, 6] have shown that, under certain conditions, one or more spatially subharmonic beams may arise between two pump beams (see Fig. 1).
Spatial Subharmonic Generation in BaTiO3
Authors: Novikov A. , Odoulov S. , Jungen R. , Tschudi T.
Published: February 2023

Generation of spatial subharmonics is considered as a consequence of convective instability in parametric nonlinear mixing of tree copropagating coherent waves of the same frequency: two incident pump waves and the scattered wave, propagating at the bisector of pump waves.
Photorefractive Effect in LEC Grown Heavily Doped n-GaAs at Picosecond DFWM
Authors: Jarasiunas K. , Roosen G.
Published: February 2023

Recently a light diffraction with photorefractive feature on transient picosecond grating in non-photorefractive geometry was observed in LEC grown semi-insulating GaAs /1/.
Space Charge Transfer and Electric Field Screening in p-i-n Structures
Authors: Ilinskii A. V. , Kutsenko A. B. , Melnikov M. B.
Published: February 2023

I. Introduction. Studying of charge transfer processes and field evolution in GaAs p-i-n structures is of interest because of applications in different electronic devices. It is considered [1] that in reversed based structures after finishing all transient processes the field distribution in bulk of i-layer has maximum strongly shifted to p- or n-layer. the shift direction depends on the impurity prevailing in i- layer; the impurity is considered to be ionized. Very often sucn assumptions are not enough valid. It is connected with complications of the method to obtain experimental information about spacial field distribution in a structure especially made of high-resistivity crystals with low impurity concentra- 15 -3 . tion (<10 cm ). Recent investigations of high - resistivity semiconductor crystals uses electrooptic effect in determination of spacial distribution of the field and its dynamics. They enable to give up the assumptions above and to provide more accurate modeling of charge transfer and field screening processes in GaAs p-i-n structures. In resent work field dynamics was studied in reverse biased bulk p-i-n structures made of lightly doped GaAs. Field evolution in different layers of the structure after voltage application and stationary field distribution were observed at voltage range (U=IO-I4OV). Theo retical modeling of the fenomena was provided taking into account only drift transport of generated free carriers.
Thermo- and Stress-Induced Electrooptical Inhomogenuities on Lithium Tantalate Crystal Y-Cut Faces
Authors: Otko A. I. , Poplavko Yu. M. , Chizhikov S. I. , Shuvalov L. A.
Published: February 2023

Lithium tantalate LiTaO3 (LT), as well as the isostructural LiNbO3, belongs to a family of uniaxial ferroelectrics of 3m symmetry class, having unique polar axis Z||3 and three equivalent polar Y- axes, which are pyroelectrically non-active in stress free crystals.
Parametric generation of a spatial subharmonic photorefractive grating in an external dc field with a small electron drift length
Authors: Nestiorkin O. P. , Shershakov Ye. P.
Published: February 2023

Relaxation of a photorefractive grating with spatial frequency q in external dc field eo is described by well known Kukhtarev equation [1]
Dynamics of Selfdiffraction in Photorefractive Media
Authors: Semenets T.I.
Published: February 2023

The dynamics of holographic gratings recording and Bragg-matched optical erasure in nonlinear materials have been studied by several authors. This question still attracts much attention even now as we can judge from programs of several conferences and recent publications/2,3/. In this paper we study how the temporal evolution of the signal wave is changing when this wave is amplified holographically due to the beam coupling in photorefractive crystals. The solution of the well-known equations for single-trap band transport model /1/ is in the basis of our calculations. The same approach was used earlier to calculate the dynamics of self-diffraction for local-response medium and step-like onset of the pump beam intensity /4/ and gave rather good description of the experimentally observed dependences /5/. We generalize the technique to treat the mixed local/nonlocal response and consider the bell-shaped temporal envelope of the input signal and pump.
Photorefractive oscillators based on phase-locked detection mechanism
Authors: Glukhov O. P. , Nestiorkin O. P. , Zel'dovich B. Ya.
Published: February 2023

Photorefractive ring and linear oscillator with different quasi-static recording mechanisms of grating have been investigated previously.
Magnetic Circular Dichroism Study of Intrinsic and Impurity Centers in Bi12MO20 (M=GE,Ti,Si) : an Overview
Authors: Briat B.
Published: February 2023

What are the defects or impurities responsible for the photorefractive effect in Bii2MO2o (BMO 6:1)? What happens during illumination at various wavelengths? What are the microscopic centers, either diamagnetic or paramagnetic, responsible for ±e intrinsic or light / impurity induced absorption bands? One must obviously try to answer such questions if one wants to understand the observed effects and to optimize the materials for improved performances. Since 1990 *, we have conducted a systematic spectroscopic study of photochromic effects in a large variety of undoped and doped BMO 6:1 crystals of two origins As already briefly demonstrated in previous communications χ3.4, magnetic circular dichroism (MCD) offers an elegant and powerful means for a microscopic study of charge transfer processes and the identification of donnor/acceptor levels. The technique has also long been established 5 as an invaluable tool (i) to characterize the charge state and local environment of a doping rm nation metal ion; (ii> to discriminate among paramagnetic and diamagnetic centers. MCD can be defined as the differential absorption Δα (cm4) for left and right circularly polarized light when the sample is subπüted to a longitudinal magnetic field B. In zero field, BMO crystals present also a natural CD which contains interesting information. My goal here is to present an overview of our most significant results since the Aussois Topical Meeting. Quite naturally, MCD.and CD spectra have been complemented by low temperature absorption experiments in the visible and near IR regions. Note that previous CD 6,7 and MCD 8 work on BMO materials, although scarce, has all been conducted in Eastern Europe.
A New Threshold Effects in LiNbO3 :Mg.
Authors: Zaritskii I. M. , Rakitina L. G. , Konchits A. A. , Corradi G. , Polgar K.
Published: February 2023

Qualitative and quantitative change of intrinsic paramagnetic radiation defects composition is found in g-irradiated at 77 K crystals of LiNbO3:Mg, if the concentration of Mg was above a threshold Mg concentration (4 - 7 mol.%). A new effect is observed in these crystals, co-doped with Cr or Fe - an appearance of HTSC like non-resonant microwave absorption signal in near zero magnetic field at ≤ 280 K.
Tensor and Phase Properties of Second Order Polarizability Gratings in Glasses
Authors: Bolshtyansky M. A. , Churikov V. M. , Savchenko A. Yu. , Zpl’dovich B. Ya.
Published: February 2023

Photoinduced Second Harmonic Generation (PISHG) in optical fibers was widely studied last five years [1].
Low noise two wave mixing deflector
Authors: Mathey P. , Pauliat G. , Roosen G.
Published: February 2023

Our deflector scheme is derived from the two wave mixing beam steering system first proposed by D. Rak et al. [1].
Bistability in Four-Wave Mixing Reflectivity of Photorefractive InP:Fe
Authors: Ding Y. , Smandek B. , Eichlier H.J.
Published: February 2023

Degenerate Four-Wave Mixing (DFWM) in photorefractive materials has been shown to be an effective method to generate a phase conjugate beam and has been intensively studied both theoretically and experimentally [1-5].
Photorefractive Crystals in Holographic Endoscopic Metrology
Authors: von Bally G. , Dirksen D. , Matthes F.
Published: February 2023

Modern optical instrumentation increasingly requires miniaturization of the used devices as it is the case e.g. in the field of endoscopy.
Real-time holographic interferometer using the technique of phase-conjugation in BTO
Authors: Kiessling A. , Kowarschik R. , Wenke L.
Published: February 2023

1 Introduction Recently, applications of phase-conjugation[1][23][4 in photorefractive crystals to interfer-ometrv have found considerable attention. In our experiments a stable self-referencing interferometer using the phase-conjugation was built with a BTO crystal in a four-wave mixing geometry. The second pump wave which works as reconstruction wave of the interferometer has been realized by a self-pumped phase-ronjugation process in BaTiO 3 crystal. The advantages of such arrangements are *distortion-free reconstruction wave aself-alignment of the reconstruction wave * real-time process * interferometric measurements of dynamic changes of the incident wave front In the following the realization of a real-time double-exposure interferometer based on a BTO crystal for storing the holograms and using a BaTiO 3 crystal to create the reconstruction wave is discussed.
Photorefractive Properties of Bisphenol-A-4,4'-Nitroaminostilbene Mixed with Diethylaminobenzaldehyde-Diphenyl Hydrazone
Authors: Ducharme Stephen , Jones Brian , Liphardt Martin , Ervin Richard , Takacs James M. , Zhang Lei , Athalye Rajan
Published: February 2023

We report the photorefractive properties of a new polymer mixture composed of 40 wt. % benzaldehyde-diphenyl hydrazone dissolved in Bisphenol A 4,4'-nitroaminostilbene. The polymer has a response time of 0.11±0.02 sec at 1 W/cm2, an overall photorefractive sensitivity (index change per unit absorbed energy density) of 1.8±0.5 × 10−6 cm3/J.
Lithium Niobate Single Crystals; Growing and Investigating Optical Quality
Authors: Sugack D.Y. , Solskii I.M. , Gabc V.M. , Matkovskii A.O. , Mikhalevic A.T. , Kuharuck S.B.
Published: February 2023

Obtaining the lithium niobate single crystals of 80-85 mm in diameter and up to 110 mm in length of boule cylindrical part having an optical homogeneity to be used in quantum electronics and non-linear optics was the aim of present work.
Indium Doping Influence on LINBO3 Properties
Authors: Volk T.R. , Rubinina N.M. , Ivleva L.I. , Kondrat’ev V.A.
Published: February 2023

The commonness of influence of damage resistant Mg1,2 and Zn3,4 impurities on LiNbO3 properties impelled us to search for other "members" of this family.
Optical Inhomogenuities in Lithium Niobate (Ln) Crystals Concerned with Ferroelectric Collinear Domains
Authors: Otko A.I. , Nosenko A.E. , Moiseenko V.N. , Shuvalov L.A.
Published: February 2023

The method [1] of the domain structure (DS) in uniaxial ferro­electric LlNbO3 (LN) spatial visualization with conventional polarizing microscope,based, on pyroelectrooptical effect (PEOE) (arising of the refractive anomalies, induced by fields of un­screened pyro-charges on domain interfaces emerging due to sui­table thermotreating), is distinguished by high resolution and informativity of observable DS images.
Crystal growth and quality of Czochralski-grown iron-doped lithium niobate single crystals
Authors: Latore J. R. , Samuelson S. , Uhrin R. , Nitanda F.
Published: February 2023

Lithium niobate doped with iron is an attractive material for use in holographic memory systems due to the combination of its photorefractive properties and relative ease of growth.
Bi12SiO20 and Bi12TiO20 Photorefractive Single Crystals
Authors: Prokofiev Victor V. , Heraldo Gallo N. J. , Carvalho Jesiel F. , Hernandes Antonio C.
Published: February 2023

Photorefractive crystals Bi12SiO20 (BSO) and Bi12TiO20 (BTO) have unique electrooptic, acoustooptic and piezoelectric properties.
Photorefractive Response in Sillenite Crystals by Applying AC Electric Fields
Authors: Litvinov R. , Shandarov S. , Yakimov D.
Published: February 2023

Photorefractive response in electro-optic materials by applying ac electric field is a topic of continuing theoretical and experimental interest [1-4].
Phase Defects in a Phase-Conjugate Photorefractive-Gain Oscillator
Authors: Balzer G. , Matamontero S. , Vasnetsov M. , Tschudi T.
Published: February 2023

The ongoing interest in transverse effects in nonlinear optics has recently led to studies of two-dimensional phase defects, particularly optical vortices.
Four-Wave Mixing Phase Conjugation Reflectivity and Fidelity for Signal Wave with "Boiling" Speckle-Structure
Authors: Ivleva I.L. , Korol'kov S.A. , Lyubomudrov J.V. , Mamaev A.V. , Polozkov N.M. , Shkunov V.V.
Published: February 2023

The response of photorefractive four-wave mixing phase-conjugate mirror on time-varying speckle-signal is discussed both experimentally and theoretically. More rapid drop of reflectivity with respect to fidelity explained by shallow traps model.
Growth of Single Crystal Photo refractive Fibers of Bi12SiO20 and Bi12TiO20
Authors: Prokofiev Victor V. , de Lima Claudio J. , Andreeta Marcelio R.B. , Hernandes Antonio C. , Carvalho Jesiel F. , Kamshilin Alexei A. , Jääskeläinen Timo
Published: February 2023

Photoretractive materials have been extensively studied since they have many attractive characteristics for data storage, optical interconnections, associative memory, phase conjugation mirrors, holographic interferometry[1].
Instability of photoinduced gratings against space-charge waves in photorefractive crystals
Authors: Sturman B. I. , Ringbofer K. H.
Published: February 2023

The investigation of different instabilities of photorefractive gratings was motivated by experiments showing the generation of subharmonics in photorefractive BSO crystals [1, 2, 3].
Novel technique for writing long superstructured fiber Bragg gratings
Authors: Stubbe Raoul , Sahlgren Bengt , Sandgren Simon , Asseh Adel
Published: February 2023

We have developed and demonstrated a novel technique to manufacture very long and superstructured gratings based on writing a set of consecutive subgratings with interferometric control of the relative position between the subgratings.
Second-harmonic measurements in UV-assisted electrically-poled glasses
Authors: Liu A. C. , Digonnet M. J. F. , Kino G. S.
Published: February 2023

We report measurements of the nonlinearity induced in different glasses by UV-assisted electrical poling. Nonlinearities are found to be at best comparable to that of thermally-poled silica.
Directly UV-written Erbium Doped Waveguides
Authors: Hübner Jörg , Feuchter Thomas , Poulsen Christian V. , Kristensen Martin
Published: February 2023

We have produced UV-written, erbium-doped glass waveguides. A planar, three-layer structure (buffer/erbium-doped core/cladding) is exposed to 193 nm excimer laser light through an aluminum mask.