bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Order Diffraction in Photorefractive Quantum Well Structures
Authors: Wang Q. N. , Nolte D.D. , Melloch M.R.
Published: February 2023

Recently, the high speed of semiconductor materials was combined with the large optical nonlinearity of the Franz-Kelydish effect near the quantum confined exciton absorption within semi-insulating multiple quantum well structures (SIMQW)[1]. The diffraction efficiency of four wave mixing obtained in the SIMQW with an optical interaction length of 1.05 µm is comparable with the diffraction efficiency for a semiconductor bulk sample with an optical interaction length of several mm operating under similar conditions. Thus, SIMQW become a ideal candidate to study the diffraction process in the Raman-Nath regime[2]. Here, we report two effects of the second order diffraction in a SIMQW sample under applied field: 1) the direct observation of a strong second order diffraction signal; 2) the intensity of the degenerate four wave mixing signal depends on the direction of applied field when the fringe spacing becomes large.
Beam Fanning in Coupled-Wave Theory of 2-Beam Coupling
Authors: Ewbank M. D. , Vachss F. R. , Vazquez R. A.
Published: February 2023

Simple coupled-wave theory1,2 accounts for depletion of the pump beam due to energy transfer (i.e., amplification) to the probe beam. Ignoring absorption, the probe gain g can be expressed as1 where I1(0) is the incident probe intensity, Γ is the two-beam-coupling coefficient and rpp is the incident pump-to-probe beam ratio given by (2) with I2(0) being the incident pump intensity.
Instabilities in photorefractive bidirectional ring oscillators
Authors: He Q. Byron , Campbell Scott , Gu Claire , Yel Pochi
Published: February 2023

Photorefractive bidirectional ring oscillation was demonstrated experimentally some time ago [1]. Recently, a theory for the bidirectional oscillation in photorefractive ring resonators was proposed [2]. Interesting properties, such as intensity thresholding effect, may find applications in the fields of optical computing and optical neural networks [3]. Although, the steady stade oscillations are undstood, the stability of those oscillations has not been addressed. In this paper we present the linear stability analysis of photorefractive bidirectional ring oscillation under mean-field approximation and experimental confirmation of unstable oscillations.
Spatial Structure of Scattered Radiation in a Self-Pumped Photorefractive Passive Ring Mirror
Authors: Korol’kov S. A. , Kuz’minov Yu. S. , Mamaev A. V. , Shkunov V. V. , Zozulya A. A.
Published: February 2023

We present detailed experimental investigation of scattered radiation spatial structure in the geometry of a transmission grating photorefractive passive ring mirror (Fig. 1) and compare our results with the predictions of Ref.[1]. According to the theory, behaviour of a ring mirror in the limit of large Fresnel numbers is determined by two scale variation coefficients: α// and α⊥. Scale variation coefficient α// is the ratio of the width of the pumping beam 4 in the plane of intersection to that of the pumping beam 2 (see Fig. 1). For | α// | <1 beam 4 is narrower and for | α// | >1 wider, than beam 2. The same with the scale variation coefficient α⊥, but for the direction, perpendicular to the intersection plane.
Image-degradation in a two-wave mixing spatial-light modulator
Authors: Notni G. , Kowarschik R.
Published: February 2023

Optical real-time image processing by spatial light modulators (SLM’s) that utilize photorefractive crystals has attracted much attention /1/. The two-wave mixing SLM is based on the selective spatial erasure of the uniform phase volume hologram created by the two plane coherent beams using an incoherent image bearing beam
Iinc(r→) resulting in an additional spatial modulation of the refractive index distribution
I1(r→) (commonly with a greater spatial period then the grating period of the hologram). The parameters of these Bragg-type SLM’s are strongly determined by the diffraction properties of the nonuniform volume gratings and are analyzed here by means of the two-wave mixing coupled-wave formalism in it’s two-dimensional description /2/.
Detection of Low Intensity Optical Wavefronts Using Noise Reduction Techniques in Photorefractive Amplifiers
Authors: Rajbenbach H. , Delboulbé A. , Huignard J.P.
Published: February 2023

Noise reduction techniques in photorefractive amplifiers are centrally important for numerous applications in image processing, pattern recognition and detection of ultra-low optical wavefronts. Recently original techniques for reducing the optical noise were proposed and experimentally demonstrated(1-3). Rotating the crystal is a very general method which successfully removes the amplified scattered noise and the multiple interface parasite reflections. In this paper, we propose an alternative for which no mechanical movement is required. As will detailed in the following, this new noise reduction method is mostly suited to photorefractive materials which exhibit a strong resonance of the two-wave mixing gain around the optimum angle between the injected signal and the pump beam.
High Resolution Volume Holography using Orthogonal Data Storage
Authors: Yariv Amnon , Rakuljic George , Leyva Victor
Published: February 2023

Holographic volume data storage has long been an intriguing subject of research interest. The main reason for this interest is the promise of enormous data storage capacities. In a long volume, storage of 1012 bits or more is possible using visible light (1). However, to date, all attempts at attaining and demonstrating a volume holographic data storage system of this density have fallen far short of this theoretical limit (2-6). Although materials limitations contributed to this shortcoming, of more fundamental importance, however, were the problems associated with the angular multiplexing schemes used to holographically access the volume of the storage medium (7-9).
Angular Selectivity of Holographic Gratings in BSO
Authors: Tao S. , Selviah D.R. , Mobasher B. , Poon P. , Midwinter J.E.
Published: February 2023

Optics offers the promise of large number of weighted parallel interconnects for use in optical neural networks. However, to date the maximum number of holographic interconnects stored in any photorefractive crystal was 500 in Fe:LiNbO3. It has not yet been established what are the fundamental limits to the maximum number of angularly multiplexed gratings. One relevant parameter is the angular selectivity of a holographic grating. In this paper we compare the theoretical angular selectivity calculated by coupled wave theory with our experimental measurement of the same quantity for a crystal of BSO. BSO has the advantage for optical interconnects that it has a higher sensitivity than Fe:LiNbO3, so lower power laser can be used for recording.
An Imaging Method for Non Linear Medium Characteristic Measurements
Authors: Boudebs G. , Phu X. Nguyen , Lecoq J.P. , Sylla M. , Rivoire G.
Published: February 2023

A non linear medium is placed in the focal plane of a 4f set up (fig.1). The Fourier spectrum S(u) induces phase and amplitude changes inside the material [1].
Photogalvanic Holographic Gratings in the Stroncium Barium Niobate Crystals (SBN: Ce).
Authors: Gnatovskii A. , Kukhtarev N. , Pigida A. , Verbitskii V. , Bogodaev N. , Polozkov N.
Published: February 2023

Photogalvanic holographic gratings were recorded in the photorefractive crystal Sr0.39Ba0.61Nb2O6 : Ce (0.05 weight %) by HeNe laser (λ=0.633m). When holographic grating vector was prpendicular to the
c→ axis hologram writing with orthogonally polarized waves were realized with diffraction efficiency of 6% (for thickness 1.0 mm). Intermode scattering [11 was observed in accordance to calculations and photoinduced holographic electric field was estimated to be about 600 V/cm. Photogalvanic holographic grating, recorded with orthogonally polarized waves may be used for phase conjugation with polarization restoration [2,3], and for processing of laser beams.
Homogeneity of the photorefractive effect in reduced and unreduced KNbO3 crystals
Authors: Amrhein P. , Günter P.
Published: February 2023

It is obvious that the homogeneity of the photorefractive sensitivity has strong influence on devices such as optically driven spatial light modulators (SLM) 1-3. These applications involve two-dimensional image information and need position-independent transfer functions. The photorefractive homogeneity is based on the distribution of the photorefractive donor centers and traps in the crystal. Therefore it is affected by the crystal growth conditions and subsequent crystal treatments such as poling and electro-chemical reduction 4, 5.
Phase conjugate techniques for diode laser brightness enhancement
Authors: MacCormack Stuart , Eason Robert W.
Published: February 2023

Diode laser arrays provide a compact, high power, high efficiency source of monochromatic light and are finding many applications in all solid-state mini and micro-laser systems. Unfortunately, the preferred modes of operation of free-running, conventional gain-guided laser arrays involve the simultaneous oscillation of many array transverse modes1. This results in an undesirable broadened twin-lobe output in the far field which is generally several times the diffraction limit of the emitting region. This leads to poor focussability which in turn severely limits the efficiency of launching into optical fibers, coupling into planar waveguides and longitudinal pumping of solid-state micro-lasers.
Power stabilization in photorefractive two wave mixing by frequency tuning of laser diode
Authors: Shimura Tsutomu , Miao Hai Yan , Itoh Masahide , Okamura Hideki , Kuroda Kazuo , Ogura Iwao
Published: February 2023

In photorefractive two wave mixing (TWM) using a BaTiO3, output power of amplified signal beam is often fluctuating. The amplification factor is very sensitive to disturbances such as mechanical vibration and fluctuation of the wavelength of the laser. It becomes a serious problem when we use TWM in optical information processing systems. We tried to stabilize the output power of the probe beam using a laser diode (LD) and feedback loop.
Influence of Piezoelectric and Photoelastic Effects on Pulse Holotgram Recording in Photorefractive Crystals
Authors: Litvinov R. , Shandarov S.
Published: February 2023

In paper1 the effective recording of hologram gratings in photorefractive cryctals by short light pulses was studied experimentally. The self-diffracthion theory of light pulses for the time of Maxwell’s relaxation τm which was negligible compared with the pulse duration τu was investigated by Kuchtarev and Semenetz2. Here we did not take into account the influence of piezoelectric and photoelastic effects that might have a strong influence on hologram recording and restoration3. The results of the analysis of hologram grating pulse recording in photorefractive crystals accounting for piesoelectric and photoelastic effects for τu«τm.
Simultaneous Diffraction of Two Light Waves in Cubic Optically Active Photorefractive Piezocrystals
Authors: Shepelevich V.V. , Egorov N.N.
Published: February 2023

The influence of optical activity on two-beam coupling in a (110)-cut cubic photorefractive Bi12SiO20 crystal has been investigated in a number of papers (e.g., [1,2]) for the case of two typical configurations
K→‖[001] and
K→‖[001], where
K→ is the grating vector. The simultaneous diffraction of two light beams has been considered in [3] for arbitrary orientation of the vector
K→ from the point of view of the electrooptic grating model. However, the results of [4] testify to the necessity of taking into account the piezoelectric and photoelastic properties of the crystal during the process of refractive index grating formation.
Investigation of photorefractive self pumped phase conjugators in the presence of loss and high modulation depth
Authors: Millerd James E. , Koehler Steffen D. , Garmire Elsa M. , Klein Marvin B.
Published: February 2023

We have recently demonstrated large two beam coupling gains in lnP:Fe by combining the band-edge resonance technique with a second resonant enhancement involving temperature stabilization.1 While loss increases near the band-edge, the gain increases much more dramatically. Net gain coefficients larger than 20 cm−1 have been measured making semiconductor gains comparable to those in ferroelectric materials. We present here an investigation of this material as a self pumped phase conjugator.
Perturbative Analysis of Higher Order Photorefractive Effect
Authors: Saxena R. , Chang T. Y.
Published: February 2023

Analytic expressions are derived for second- and third-order photorefractive effect. The dependence on spatial frequency, applied field, and velocity of moving grating is examined.
The Effect of Large Signals in Photorefractive Media
Authors: Powell A. K. , Fish D. , Barrett G. R. , Hall T. J.
Published: February 2023

Photorefractive materials remain of interest as optically nonlinear elements, because of the large saturated nonlinear effects that they exhibit at low continuous wave optical power levels. They can be used to give large optical amplification to image bearing beams by utilising the nonlinear process of two-wave mixing. Four-wave mixing can also be achieved, and phase conjugate reflectivities of signal beams can be substantially greater than unity. Self-pumped phase conjugation is also possible in those photorefractive materials with nonlinearities that are suitably large.
Dynamic Solutions and Instabilities of the Four-wave Mixing Interaction Utilising the Underlying SU(2) Group Symmetry
Authors: Barrett G. R. , Powell A. K. , Hall T. J.
Published: February 2023

Optical phase conjugation is an important nonlinear process, with many applications in the areas of optical communications and optical processing. This is as a result of the wave-front correction properties that phase conjugation offers and this has generated much interest in the area. A common method of producing phase conjugated wavefronts is the four-wave mixing interaction and many publications on the steady state solution to this problem have appeared over the last decade. More recently, however, interest has been focussed upon the temporal behaviour of four-wave mixing systems, with instabilities and chaos being both demonstrated by Gauthier et al [1] and predicted by Królikowski et al [2].

To date, the analysis for the temporal behaviour of anisotropic four wave mixing, in the transmission grating regime, has involved the direct numerical integration of the equations describing four wave mixing. This analysis however, does not utilise the symmetries of the four wave mixing process, and thus results in a more complex problem. Through exploitation of these symmetries the complexity of the problem has been reduced from one containing four complex variables, to one containing three real variables. This has been accomplished through the use of the Special Unitary Group 2, a group providing a two dimensional matrix, whose elements are functions of three real variables. The multiplication of this matrix, together with one containing the boundary conditions for the problem, thus enables the four complex beam amplitudes to be reexpressed in terms of three real quantities. Using this technique, the temporal nature of anisotropic four wave mixing has been studied, and shown under certain conditions, to exhibit chaotic behaviour when an electric field is present. The effect of any material absorption on the chaotic nature is also demonstrated.
Single Crystal Growth of Photorefractive Sillenites
Authors: Volkov V.V. , Kargin Yu.F. , Skorikov V.M.
Published: February 2023

The compounds, crystallized in the cubic form similar to sillenite structure, occur in a number of isomorphs [1]. The well-known representatives of this family are bismuth germanium (BGO) and bismuth sillicon oxides (BSO), both of which can be grown from their stoichiometric melts using Czochralsky technique. The optical examination and utilization of the iso­morphs are difficult because of their incongruent melting or decomposition in solid state.
Temperature dependence of the two beam coupling gain coefficient of photorefractive GaP
Authors: Kuroda K. , Okazaki Y. , Shimura T. , Itoh M.
Published: February 2023

Undoped semi-insulating GaP is photorefractive material which is sensitive to the laser light of the wavelength between 0.6 μm and 0.9 μm1). He-Ne lasers and GaAlAs laser diodes belong to this spectral region. This material is important for constructing compact systems with laser diodes.
Electronics, Optics, and the Photorefractive Effect
Authors: Williamson Richard C.
Published: February 2023

Summary not available.
Optics, Electronics, and the Photorefractive Effect
Authors: Psaltis Demetri
Published: February 2023

Summary not available.
Crystal noise limited holographic interferometry in BSO
Authors: Troth R. C. , Dainty J. C. , Sochava S. L. , Stepanov S. I.
Published: February 2023

There are two geometries that are generally used for real-time interferometry, the four wave mixing (FWM)1,2 and two beam coupling (TBC)3,4 geometries. There is, however, a geometry which incorporates features of both FWM and TBC proposed by Petrov et.al.5 and it is this geometry which is easiest to implement and gives good results. In this geometry the anisotropic self diffraction properties of sillenite crystals such as Bi12(Ge, Si, Ti)O20 are used to produce a polarization rotation between the incident and diffracted beams. Thus if one of the above crystals is placed in the standard FWM orientation, with the [110] crystalographic direction in the plane of the incident beams, such that the axes of charge induced birefringence are at ±45° to the [001] direction (Fig.1), then the transmitted object (signal) beam can be cancelled by using two orthogonal polarizers placed in front of and behind the crystal. This enables the diffracted image to be isolated from the signal so reducing the effective noise in the output hologram. Rather good time-average and double exposure interferograms can be produced6,7, (Fig.2), with, however, a restriction on the size of the object that can be investigated, when the object is diffusely reflecting. In the case of the time-average interferogram shown in (Fig.2) the object was only 40 mm in diameter. The restriction on object size is partly due to geometrical considerations but is also strongly dependent on the noise and sensitivity characteristics of the crystal used. For this reason we present here an analysis of two samples of Bi12SiO20 (BSO) crystals grown in different laboratories, based on a simple theory for the determination of maximum viewable object size, from material considerations.
Frequency Shift in a Mutually Pumped Phase Conjugator of BaTiO3
Authors: Wang Dadi , Zhang Zhiguo , Ye Peixian
Published: February 2023

Since the observation of self-frequncy scaning with a passive phase-conjugate mirror coupled to a dye-laser cavity in 1984, much attention has been paid to frequency detuning in photorefractive (PR) wave mixing. Such a phenomenon has been widely studied in various photorefractive oscillators.(1) In this paper, we present the experimental results of frequency shift (f-shift) in our mutually pumed phase conjugator (Bridge conjugator)(2) and demonstrated to be dramatically dependent upon the power density of pumping beams.
Anisotropic Diffraction in Photorefractive Volume Hologram
Authors: Sun Ching-Cherng , Chang Ming-Wen
Published: February 2023

Recently, there are extensive studies on applying the photorefractive effect for optical data storage and processing[1][2]. One of the most important applications is for the volume holographic storage. In this paper we report theoretical derivations and experimental results on the important properties of the anisotropic diffraction in a photorefractive volume hologram in a BaTiO3. As we shall see, the diffraction efficiency, the angular sensitivity, and the optimal reconstructing angle for obtaining the maximum diffraction efficiency depend very much on the grating vector and crystal orientations. The crystal orientation and the light beam directions are shown in Fig.1. In order to avoid the beam coupling phenomena[3], we use S-polarized light for writing holograms and P-polarized light for reconstruction.
Photorefractive Deamplification for Artifact Noise Reduction
Authors: Khoury Jehad , Cronin-Golomb Mark , Woods Charles L.
Published: February 2023

Many optical image processing operations such as edge enhancement may be performed by suitable linear spatial filters. A broader class of operations is made available by extending this technique to nonlinear filters. An example of this is the use of a logarithmic nonlinearity for conversion of multiplicative to additive noise [1]. In this work, we demonstrate that phase preserving thresholding in the Fourier plane which linearly transmits signals above a certain intensity, reduces additive signal dependent noise, such as noise from coherent artifacts, image defects and uniformity noise.
Stability of Information Readout by Self-pumped Phase Conjugation in Barium Titanate
Authors: Lin F. C. , Sun D. , Leu G. , Fiddy M. A. , Yang T. , Teng Y. Y.
Published: February 2023

For real-time optical image storage and processing, we have systematically studied self-pumped phase conjugation (SPPC) [1] in barium titanate (BaTiO3) crystals (from Sanders Associates Inc., Merrimack, NH) in terms of the incident angle θ, the impact position l on the crystal surface, the distance L between the imaging lens and the impact point on the crystal face [Figure 1], the argon-ion laser power P (p-wave with various wavelengths), and the ambient temperature T. We found that the stability of the temporal SPPC intensity IPC (t) strongly depends on these geometrical parameters, θ, l, and L. The objective in this paper is to identify optimal conditions in order to stablize and maximize the temporal evolution of the SPPC reflectivity R(t) which is defined as the ratio of IPC (t) to the intensity IM retro-reflected by a mirror at the position of the crystal to the detector. We have defined the optimal (or stable) condition for the SPPC as |Rmax-R(t)|/Rmax ≤ 0.1, where Rmax is the maximum value of R(t) (recorded within 10 minutes to 1 hour) and also the maximum value in terms of the above geometrical and physical parameters.
Effects of Grating Erasure on Beam Fanning and Self-Pumped Phase Conjugation
Authors: Wood Gary L. , Clark William W. , sharp Edward J. , Salamo Gregory J.
Published: February 2023

The photorefractive phenomena of beam fanning and phase conjugation have been used to demonstrate such operations as optical limiting, interconnecting, tracking, and a wide variety of applications utilizing phase conjugate mirrors. Many other applications can be realized when two laser beams interact in a photorefractive crystal since one of the beams can be used to control the other. For example, it is possible to amplify, deplete, direct, switch, or modulate one of the beams with the other. The photorefractive effect provides the underlying mechanism for these demonstrations of all-optical light by light control. These applications depend upon the formation of particular photorefractive gratings and the perturbation of those gratings. Only recently has attention been given to the importance of the physical location of the gratings within the crystal.1,2,3
Extraordinary polarised light does not always yield the highest reflectivity from Self-Pumped BaTiO3
Authors: James Stephen W. , Eason Robert W.
Published: February 2023

The ’Cat-Mirror’ Self Pumped Phase Conjugator, SPPC, has continued to stimulate research since its discovery in 19821. Surgical erasure of photorefractive gratings has been used in attempts to locate principle interaction regions in the conjugator2,3, and also to control the magnitude and temporal behaviour of the phase conjugate output4.
Self-Pumped Phase Conjugation in BaTiO3:Ce
Authors: Guruswamy Chitra , Temple Doyle A.
Published: February 2023

Barium titanate is important as a nonlinear optical material primarily because of its large photorefractive gain. This gain is large enough to give rise to self-pumped phase conjugation at low optical power 1 Several studies have been conducted on enhancing the gain of the crystal through controlled doping2-5 and annealing.3,6,7 These dopants have, till now, been confined to transition metals such as iron,2,3 chromium,4 iron + nickel,5 and cobalt.5 In this talk, we report preliminary results of the self-pumped phase conjugate reflectivity in cerium doped barium titanate.
Multiple Grating Optical Processing in Barium Titanate
Authors: Boothroyd S.A. , Beckwith P.H. , Chan L. , Chrostowski J.
Published: February 2023

Nonlinear optical image subtraction and Boolean XOR operations have been demonstrated in Michelson interferometers with phase conjugate mirrors [1-3], The two interferometer arms each contain a light modulating transmission or reflection element which must be carefully registered and imaged at the interferometer output. Destructive interference between the output images of the two arms arises because one image undergoes a extra π phase change on reflection from a dielectric interface. Image subtraction has also been achieved in photorefractives via double exposure holography [4] where two gratings are formed by displacing the reference beam in phase by π. A π phase shift on one of the writing beams in four wave mixing has also been used to selectively erase volume holograms in photoreffactive media [5-7].
Phase Conjugation with Saturable Gain and Saturable Absorption
Authors: Belić Milivoj , Timotijević Dejan , Boyd Robert W.
Published: February 2023

We have investigated 2WM and 4WM processes in photorefractive crystals in the nonsaturated regime, i.e. when the coupling between beams and the absorption depend on the light intensity. Different models of saturable absorption in 2WM via reflection grating are considered, and the corresponding wave equations are solved exactly. The solutions are written in terms of hypergeometric functions or in quadratures. From the solutions it was found that the energy transfer between the waves is less effective in the nonsaturated stage of the process.
Instabilities in Coupled Photorefractive Ring Cavities and Self-Pumped Phase Conjugators
Authors: Dai Li-Kuo , Gou Yih-Shun , Gu Claire , Yeh Pochi
Published: February 2023

Photorefractive mode coupling between resonators provides a simple model for self-pumped phase conjugators [1] where instabilities may occur due to energy transfer between different oscillation modes inside the crystal. In this paper, we consider the dynamical behaviors of mode coupling between two unidirectional ring resonators [2]. The first resonator is driven by an external laser beam via photorefractive two-wave mixing. The internal oscillating beam is then employed to drive the second ring resonator via the same mechanism (see Fig.1).
Investigation of Photorefractive Waveguides Fabricated by Excimer Laser Ablation and Ion-Implantation
Authors: Youden K.E. , Eason R.W. , Gower M.C.
Published: February 2023

The fabrication of thin films optical waveguides of photorefractive materials is particularly desirable for applications in integrated optics. It is also of interest because the guided-wave intensity-length product can be considerably larger than in bulk media because of the optical confinement within the waveguide. The increased intensity-length product may therefore allow much faster response times than in the bulk (typically by a factor of ≈103-l04). Thin crystalline films can be fabricated by a variety of techniques such as RF sputtering, flash evaporation, molecular beam epitaxy and liquid phase epitaxy. However, the films grown are often of the incorrect (or variable) composition and phase and are rarely of good optical quality. We discuss here two methods that we have investigated for producing optical waveguides in several different photorefractive materials.
Nanosecond Photorefractive Effects in KNbO3
Authors: Biaggio I. , Zgonik M. , Günter P.
Published: February 2023

Two laser beams interfering in a photorefractive crystal ionize light absorbing impurities and produce two initially overlapping concentration gratings. These two gratings consist of ionized donors that are immobile and of free charges that can move due to diffusion in a concentration gradient and drift in an external or internal electric field. Spatial separation between the two gratings produces a space-charge field which modulates the refractive indices of the crystal via the linear electro-optic effect. The photorefractive effect can be efficiently employed for two-wave and four-wave mixing already at the low light-intensities obtained with CW lasers [1]. The trade-off connected with low power optical beams is a decrease in response time. The photorefractive index change depends on the optical energy absorbed and not on the instantaneous optical intensity. In order to increase the speed of response beyond the limit given by the photogeneration rate one must use high intensity laser pulses. Photorefractive diffraction gratings with sub-microsecond response-times were already measured in LiNbO3[2], BaTiO3[3,4], KNbO3[5,6,15], and Bi12SiO20[7,8]. KNbO3 is known for its large linear electro-optic (EO) and second-order nonlinear optical coefficients. When chemically reduced the photorefractive response time decreases [9-11].
Feature extraction by a self-organizing photorefractive system
Authors: Benkert Claus , Hehler Verena , Jang Ju-Seog , Rehman Shakil , Saffman Mark , Anderson Dana Z.
Published: February 2023

An important feature of neural network processing lies in a network’s ability to adapt to a given problem. The adaptation is accomplished by modifying its internal structure through some learning procedure. Neural network models may be classified in one of two types: The learning may be supervised by someone or something that indicates to the network what is expected of it, or the network may be governed by a self-organizing process in which it automatically develops an internal state that reflects the properties of its input environment. Self-organizing systems need no a priori knowledge supplied by a supervisor, and are particularly valuable when the task of the system depends only upon some property of the input data itself.
All-Optical Associative Memory based on a Nonresonant Cavity with Image Bearing Beams
Authors: Ingold M. , Duelli M. , Günter P. , Schadt M.
Published: February 2023

A new configuration of an all-optical, nonlinear holographic associative memory [1] is investigated. A multistable, content-addressable cavity is used, that performs image comparison, discrimination and read-out in one step. The required nonlinear processes are obtained by using a combination of a photorefractive KNbO3 crystal and a nematic liquid crystal (NLC) in a feedback configuration with several beams.
Detection of the transient motion of a scattering surface by two-wave mixing in a photorefractive crystal
Authors: Ing R. K. , Monchalin J.-P.
Published: February 2023

Optical detection of the transient surface motion of objects is an area of far reaching practical importance. Applications include the vibration monitoring of many engineering structures (power plants, aircrafts, engines of various kinds...) and more recently the detection of ultrasound produced by pulse laser excitation. This technique, now in active development in our laboratory and elsewhere, extends ultrasonic inspection of materials to conditions otherwise difficult or impossible (complex geometries, hot products on a production line...). Various optical systems have been devised for detecting surface motion and have been recently reviewed1. We are reporting here the novel use of two wave mixing in a photorefractive crystal for detecting such a motion and in particular ultrasonic displacement produced by pulsed laser excitation. This approach has the merit of being applicable to a rough surface by integrating over many speckles and of having a very broad frequency detection bandwidth. The use of two-wave mixing for coherent homodyne detection of arbitrary wavefronts was previously reported and applied to the detection and amplification of an intensity modulated wave2. In the case of interest here of the detection of surface motion, the signal wave which has been scattered off the surface is instead phase modulated, and the scheme previously reported cannot be directly used since the transmitted signal wave and the diffracted pump wave, which acts as local oscillator, are in phase. Linear and sensitive detection of phase shifts requires instead the interfering light fields to be in quadrature. Before describing an optical configuration which satisfies this requirement, we analyze the effect of a small phase shift applied to the signal wave in a two-wave mixing configuration.
Grating Formation in Strontium Barium Niobate using Picosecond Laser Pulses
Authors: Holmstrom Scott A. , Taheri Bahman , Reeves Roger J.
Published: February 2023

Photoinduced gatings were established in nominally undoped and iron-doped strontium barium niobate, SrxBa1-xNb2O6, x=0.60 (SBN:60), using a single, frequency doubled pulse from a Q-switched and mode locked Nd:YAG laser.
Photorefractive Effect in InP:Fe Under High Electric Field
Authors: Turki K. , Picoli G. , Wolffer N. , Gravey Ph.
Published: February 2023

Fe-doped InP is a promising photorefractive material offering the possibility of implementing optical processing functions at IR wavelengths compatible with semiconductor lasers and optical communication applications.
Combined Effects of Thermal Fixing and Beam Coupling in Photorefractive Materials
Authors: Jeganathan Muthu , Hesselink Lambertus
Published: February 2023

To avoid erasure of holograms, recorded in photorefactive materials, during readout several fixing techniques have been used.
Anisotropic Four-Wave Mixing in Optical Waveguides
Authors: Kip D. , Krätzig E.
Published: February 2023

Photorefractive crystals like LiNbO3, KNbO3 or BaTiO3 are suitable media for frequency degenerate two- and four-wave mixing allowing for amplification and phase conjugation of coherent light beams [1, 2].
Photorefractive Gratings in Planar Waveguides in Electro-Optic Cubic Crystals
Authors: Salikaev Y. , Shandarov S.
Published: February 2023

The photorefractive gratings formation in planar waveguides has been described in Refs. 1-3. LiNb03 single crystal doped of the impurities Fe or Cu was used as substrate of photorefractive waveguides [4]. Photorefractive gratings formation in that waveguides is due to the photovoltaic effect.
Electron-hole competition in dynamic hologram recording in cadmium telluride
Authors: Odoulov S. G. , Shcherbin K. V. , Shumelyuk A. N. , Fochuk P. M. , Panchuk O. E.
Published: February 2023

It is well known that noncentrosymmetric cubic semiconductor crystals offer the possibility of the recording of shifted dynamic gratings due to diffusion charge transport which in turn leads to intensity coupling of two recording waves [1,2].
Photorefractivity in CdSe
Authors: Korneev N. A. , Stepanov S. I.
Published: February 2023

CdSe is a well-known photoconductive material with high sensitivity in visible and near IR [1,2].
Photostimulated Pyro— and Piezoelctric Local Fields in LiNbO3
Authors: Kanaev I.F. , Malinovsky V. K. , Pugachev A. M. , Surovtsev N. V.
Published: February 2023

It was reported /1,2/ on a new electric response in LiNbO3 which was not distinguished previously, under a short-time (τp = 50 ns) high-power ruby laser pulse.
Pyroelectrically-Induced Charge Redistribution in BaTiO3 and KNbO3
Authors: Buse K. , Krätzig E.
Published: February 2023

We demonstrate experimentally the influence of a pyroelectric charge driving force on photorefractive currents for the first time.
Rings and Lines of Scattered Light in Photorefractive Crystals
Authors: Sturman B.I.
Published: February 2023

The proposed theory is the result of generalization of the experience in description of different kinds of the conical scattering in photorefractive crystals for optical configuration with two pump beams. The numerous experimental data (see f.i. [1]) and the theoretical paper [2] served as prerequisites.
Non-steady-state Photocurrent in GaAs in the Presence of an External Magnetic Field
Authors: Sochava. S. L. , Stepanov S. I
Published: February 2023

Excitation of an alternating through current inside a photoconductive crystal illuminated by an. oscillating interference patυβrn was first- observed in 1986 [1). It is caused by a time-dependent phase shift between the free carrier and space charge field distributions.. Investiga tions of this current give information about such important parameters of the light-induced charge transfer as the sign of ths charge carriei3, diffusion length, M-xwell relaxation time, free charge carrier lifetime, etc. Originally this so-called "non-steady-state photocurrent technique was proposed to characterize the sillenite type crystals (BSO). Later it was used for investigation of semiconductor GaAs [2] and ferroelectric EaTiOj [3] crystals. In this contribution we report the first, to our knowledge, results of the study of the non-steady-state photocurrent ir the presence of an external magnetic field.
Laser-stimulated variation of refractive index in superficial region of semiconductor CdS crystals.
Authors: Oleksenko P.Ph. , Kamuz A.M. , Ovsyannikov Y.U.
Published: February 2023

Considerable recent attention has been focused on laser- stimulated processes in semiconductors, due to prospects of their use in microelectronics.
Two- And Four- Wave Mixing in Ba2NaNb5O15 Crystal in an External Detecting Field
Authors: Novikov A. D. , Nestiorkin O. P. , Shershakov Ye. P. , Zel’dovich B. Ya.
Published: February 2023

A static hologram recorded by different frequency beams in a photorefractive Bi12TiO20 crystal in the external ac field, which was called as phase-locked detection mechanism, has been suggested and realized experimentally [1-3].
Anomalous Properties of Recording and Replay of x(2) Gratings in Glasses.
Authors: Bolshtyansky M. A. , Churikov V. M. , Savchenko A. Yu. , Zel’dovich B. Ya.
Published: February 2023

Despite a lot of publications the physical mechanism of photoinduced second harmonic generation in optical fibers [1] is not understood yet.
Photorefractive Effects in Langmuir-Blodgett Films
Authors: Gaididei Yu. B. , Trofimov A. S.
Published: February 2023

The structural transitions in Langmuir-Blodgett films irradiated by light are discussed.
Phase conjugation and amplification due to two wave interaction in photorefractive ВаТiOз
Authors: Rauch T. , Balzer G. , Sedlatschek M. , Schäfer T. , Tschudi T.
Published: February 2023

We present the characteristics and applications of a system providing phase conjugation and amplification of optical signals by two wave interaction in photorefractive BaTiO3.
Polarization State of Diffracted Beams from Anisotropic Gratings Formed in Photorefractive Material
Authors: Han Chien-Wei , Campbell Eugene W.
Published: February 2023

A method of determining the state of polarization of diffracted beams caused by a volume grating formed in photorefractive material is presented by using the rigorous coupled-wave model developed by Glytsis and Gaylord1.
Amplitude and Phase Measurement in Photorefractive Time- Average Interferometry: A Comparison with Electronic Speckle Pattern Interferometry
Authors: Rohleder H. , Petersen P. M. , Marrakehi A.
Published: February 2023

Time-average interferometry of vibrating diffusely scattering structures was introduced by Powell and Stetson in 1967.1
Photovoltaic and Photorefractive Ferroelectric Polymers
Authors: Verkhovskaya K.A. , Fridkin V.M. , Legrand J.F. , Bune A.V.
Published: February 2023

The Bulk Photovoltaic Effect (BPE) in the materials without center of symmetry is one of the fundamental properties of ferro- and piezoelectrics based on the violation in the principle of detailed balancing in nonequilibrium kinetics.
The electrooptic effect of pure and Fe doped BaTiO3 single crystals - comparison with the dielectric constants
Authors: Juliien P. , Abid Y. , Jannot B.
Published: February 2023

Perovskite oxide crystals are well known materials with large electrooptic (EO) coefficients.
Photoelectric Properties of Bi2TeO5 Single Crystals
Authors: Sadovskaya L. Ja. , Sokolianskii G.X. , Avramenko V.P.
Published: February 2023

Bismuth tellurite Bi2TeO5 is one of the most stable form of the Bi2O3-TeO2 system and has many interesting properties.
The INFLUENCE of METAL DOPINGS on the OPTICAL and ELECTROOPTICAL PROPERTIES in LiNbO3
Authors: Ped'ke B.B. , Rudyak V.M. , Shabalin A.L.
Published: February 2023

Investigations of the optical and electrooptical properties of LiNbO3 monecrystals doped by Mn,Cr,Ni,Ti,Ce,Fe, Cu and etc. metallic dopings were carried on during the years.
Transient Photovoltaic Current and Photorefraction in the Crystals with Secondary Centers
Authors: Volk T.R. , Astaf’ev S.B.
Published: February 2023

Secondary centers in photorefractive crystals (e.g.1,2) were recently shown to modify the steady bulk photovoltaic current3.
Photo- and Electrochromic Effects in Undoped and Doped Bi12SiO20 Single Crystals
Authors: Panchenko T.V. , Truseyeva N.A. , Osetsky Yu. G.
Published: February 2023

Investigation of the photochromic (PE) and electroohromic (EE) effects in Bi12SiO20 (BSO) single crystals is of great interest for optimization of PRQM-parameters and volume hologram memory devices.
Influence of Photoelasticity on Light Self Diffraction in Photorefractive Crystal of Bi12SiO20
Authors: Borshch A. , Brodin M. , Volkov V. , Kukhtarev N. , Semenets T.
Published: February 2023

An essential role of photoelasticity in light, diffraction by volume gratings in photorefractive crystals was pointed out in [1] for CW lasers.
Optimization of the Energy Transfer in Cubic Photorefractive Piezocrystals
Authors: Shepelevich V. V.
Published: February 2023

Influence of piezoelectric effect on light diffraction in photorefractive crystals was studied for the first time in [1,2] oh example of LiNbO3.
Traps recharge wave in asymmetric electric field
Authors: Dooghin A. V. , Zel’dovich B. Ya
Published: February 2023

Effect of generation of traps recharge wave (TRCW) in de electric field is employed for resonant hologram recording in photorefractive crystal [1].
A Temporal Whole Beam Propagation Method for Four Wave Mixing in Photorefractive Media
Authors: Parshall-Gujral Elaine R. , Cronin-Golomb Mark
Published: February 2023

Four wave mixing in photorefractive media is modelled using a whole beam method for wave propagation and a relaxation technique for temporal grating formation.
Two-Wave Photorefractive Coupling of Counterpropagating Beams In Multiple Quantum Well Structures
Authors: Shkunov V. V. , Zolotarev M. V.
Published: February 2023

Expectation of greatly enhanced nonlinearities in semiconductor multiple quantum well (MQW) structures has motivated extension of the study of their photorefractive properties [1-3].
Spatio-temporal resonance in generation of subharmonics, sum and difference frequencies in photorefractive crystals
Authors: Liberman V. S. , Zol’dovich B. Ya.
Published: February 2023

We consider the photorefractive crystal illuminated by light containing two interference patterns.(generally running)
Photobleaching of broadband absorptions associated with the formation of single-pulse fiber Bragg gratings
Authors: Askins C. G. , Putnam M. A. , Friebele E. J.
Published: February 2023

Broad spectral losses near 800 nm have been identified which arise concurrently with the formation of type 1 single-pulse fiber Bragg gratings. The losses can be reduced 7-fold with 640 nm light while minimally affecting Bragg reflectivity.
Mechanisms of Photo-bleaching of 5eV Absorption Band in Hydrogen Loaded Ge-doped Si O2
Authors: Awazu Koichi , Onuki Hideo , Muta Ken-ichi
Published: February 2023

It has been well known that the optical absorption band at 5eV exists in Ge doped a-SiO2. Some origins of photosensitivity are proposed [1] and undoubtedly one of them is related to the origin of 5eV band [2]. Two kinds of different defects have responsibility on the absorption band at 5eV, one is a neutral oxygen vacancy (NOV) peaking at 5.06eV and the other is a Ge lone pair center (GLPC) at 5.14eV [3]. Hosono et al. reported that the NOV was photochemically converted into Ge E' center [2]. Recently, a maximum refractive-index change A of 1% has been reported in hydrogen-loaded germsnosilicate fibers. In this article, photochemical reactions in H2 loaded Ge-doped a-SiO2 were examined [4].
Fiber Optic Bragg Grating Sensor Systems for Multi-point Distributed Strain Monitoring
Authors: Kersey Alan D.
Published: February 2023

Fiber Bragg grating (FBG) based sensors represent one of the most exciting developments in the area of fiber sensor technology in recent years. A wide range of sensor types and interrogation techniques is possible, and methods for addressing multiple FBG elements along a fiber have been developed. This presentation will review this rapidly emerging area of fiber sensing and describe some of the potential applications of the technology.
Photo-induced birefringence and applications in sensing
Authors: Handerek V. A. , Kanellopoulos S. E.
Published: February 2023

In the last few years optical fibre photosensitivity has been noticed to be anisotropic; that is the photoinduced index change is birefringent.[1] The photoinduced anisotropy of germanium doped silica fibres has allowed the fabrication of polarisation converting gratings analogous to mechanically produced periodic birefringent fibre structures made in the past.[2-8] Such gratings are known as polarisation couplers or rocking filters when they couple forward-travelling fibre modes and as Bragg exchange gratings when backward travelling light is produced.
Photosensitive processes in silica glass using 193 nm light
Authors: Albert Jacques
Published: February 2023

The name "Photosensitivity" is associated with the process by which the refractive index of certain types of silica glasses is permanently modified by exposure to short wavelength optical radiation [1]. The process was discovered in germano-silicate optical fibers exposed to intense blue light (λ=488 nm) from an Argon ion laser [2] but further experiments revealed that the photoinduced index change grows as the square of the laser intensity, indicating a two-photon process[3]. It was eventually found that the photosensitivity was due to an absorption band with a maximum near 242 nm [4], similar to the absorption observed in oxygen deficient germania (i.e. GeO sites in GeO2 )[5]. With direct excitation from intense UV light in the absorption band, the refractive index change in standard optical fibers reaches 10-4 and the process becomes sufficiently efficient for writing Bragg gratings in fibers by side exposure [4],[6]. These advances have led to the developement of several important applications [7]. Finally, apart from using special fibers with enhanced photosensitivity (from higher germanium concentration, co-dopants, or processing in reducing atmospheres), two methods have been proposed to increase the photosensitivity of standard fibers: flame brushing [8] and low temperature hydrogen (H2) loading [9]. With these techniques, refractive index changes in the 10-3 -10-2 range have been reached, extending the variety of useful fiber devices and allowing other applications to become practical [10-12].