Publications

2001
E DelRe, A Ciattoni, and AJ Agranat. 2001. “Anisotropic charge displacement supporting isolated photorefractive optical needles.” Optics Letters 26 (12), Pp. 908 - 910. Publisher's Version Abstract

Strong asymmetry in the charge distribution supporting a single noninteracting spatial needle soliton in a paraelectric photorefractive is directly observed by means of electroholographic readout. Whereas in trapping conditions a quasi-circular wave is supported, the underlying double-dipolar structure can be made to support two distinct propagation modes. (C) 2001 Optical Society of America

Aharon J Agranat, Lavi Secundo, Noam Golshani, and Meir Razvag. 2001. “Wavelength-selective photonic switching in paraelectric potassium lithium tantalate niobate.” Optical Materials, 18, 1, Pp. 195 - 197. Publisher's Version Abstract
A generic wavelength-selective switching method is presented. The method is based on the voltage-controlled photorefractive effect in paraelectric crystals. The switch consists of a crystal at the paraelectric phase in which a space charge grating was stored by a photorefractive process. Diffraction occurs by the application of a uniform electric field that causes the space charge grating to induce an index grating. Results of the diffraction efficiency as a function of the applied field and the time dependence of the diffracted beam are presented. The performance envelop of a switch based on this effect is briefly discussed.
Accession Number: S0925346701001665; Author: Agranat, Aharon J. (a, ∗); Author: Secundo, Lavi (a); Author: Golshani, Noam (a); Author: Razvag, Meir (b); Affiliation: Department of Applied Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel; Affiliation: Trellis Photonics Ltd., Jerusalem Technology Park, Jerusalem 96951, Israel; Number of Pages: 3; Language: English;
2000
E DelRe, S Trillo, and AJ Agranat. 2000. “Collisions and inhomogeneous forces between solitons of different dimensionality.” Optics Letters 25 (8), Pp. 560 - 562. Publisher's Version Abstract

We exploit nonlinear propagation in photorefractive crystals to observe the phenomenology associated with the collision and interaction of solitons of different tranverse dimensions: a self-trapped stripe and a round soliton. Along with evidence of particlelike behavior, our results indicate the emergence of a new phenomenology related to the hybrid-dimensional system. (C) 2000 Optical Society of America. OCIS codes: 190.5530, 190.5330.

O Levi, G Perepelitsa, D Davidov, S Shalom, I Benjamin, R Neumann, AJ Agranat, and Y Avny. 2000. “A photo-oxidation mechanism for patterning and hologram formation in conjugated polymer/glass composites.” J. of Appl. Physics 88 (3), Pp. 1236 - 1243. Publisher's Version Abstract
Improved diffraction efficiency was observed in holograms stored in disordered conjugated polymer/glass composites. The conjugated polymers used were alkoxy substituted poly(phenylenevinylne) analogs and the glass matrices were zirconia-organosilica xerogels. Investigation of the mechanism of hologram formation revealed evidence of a photochromic process consisting of light induced photo-oxidation (bleaching) of the embedded conjugated polymer resulting in the formation of an absorption grating and a phase grating. Investigation of the hologram formation revealed that the process was oxygen dependent. Oxygen removal increases hologram formation time by more than an order of magnitude and halves the total hologram efficiency. The oxygen dependence was also highly correlated with photobleaching of the samples and beam interaction of the writing beams. The chemical transformations upon photobleaching were shown by infrared and Raman spectroscopy to involve chain scission and oxidation of the polymer at the vinylic position of the conjugated polymer. Film preparation of the composites was optimized showing a tenfold improvement in the holographic properties compared to our previous results. The optimized treatment method allows for a high, > 20%, diffraction efficiency, eta, to be obtained for the 2.5-mu m-thick polymer/glass films. Light sensitivity was compared for several polymer/glass composites and was correlated to the absorption curves and holographic diffraction efficiency showing that the new composites and film preparation techniques are promising for holographic materials sensitive in the blue and ultraviolet spectral regions. A method of information fixing by preventing oxygen entry to the composite film resulted in a fourfold increase of the erasure time. These findings suggest that holograms can be fixed for a long term by nonoxygen permeable coating, applied after hologram formation. (C) 2000 American Institute of Physics. [S0021- 8979(00)07114-0].
Gabby Bitton, Yuri Feldman, and Aharon J Agranat. 2000. “Dielectric properties of K 1−x , Li x , Ta l−y , Nby 03 crystals..” Ferroelectrics, 239, 1, Pp. 213-224. Publisher's Version
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I Segal, E Dorfman, O Yoffe, I Bezrukavnikov, and AJ Agranat. 2000. “Direct ICP-OES Determination of Cu, Fe, Li, Ti and V in Potassium Lithium Tantalate Niobate Crystals.” Atomic Spectroscopy , 21, 2, Pp. 46-49.
B Pessach, G Bartal, E Refaeli, and AJ Agranat. 2000. “Free Space Optical Cross-Connect Switch by Use of Electroholography.” Applied Optics , 39, 5, Pp. 746-758. Abstract
An electrically controlled holographic switch is proposed as a building block for a free-space optical interconnection network. The switch is based on the voltage-controlled photorefractive effect in KLTN crystals at the paraelectric phase. It is built of electrically controlled Bragg gratings stored in the volume of the crystal. A compact switch that connects four high-speed fiber-optic communication channels with high efficiency is demonstrated experimentally. The switch performance is investigated and optimized. This switch is extremely attractive for cascaded switching arrays such as those found in multistage interconnect networks.
E DelRe, M Tamburrini, and AJ Agranat. 2000. “Soliton electro-optic effects in paraelectrics.” Optics Letters 25 (13), Pp. 963 - 965. Publisher's Version Abstract

The combination of charge separation induced by the formation of a single photorefractive screening soliton and an applied external bias field in a paraelectric is shown to lead to a family of useful electro-optic guiding patterns and properties. (C) 2000 Optical Society of America.

GM Tosi-Beleffi, M Presi, E DelRe, D Boschi, C Palma, and AJ Agranat. 2000. “Stable oscillating nonlinear beams in square-wave-biased photorefractives.” Optics Letters 25 (20), Pp. 1538 - 1540. Publisher's Version Abstract

We demonstrate experimentally that, in a paraelectric, nonstationary boundary conditions can dynamically halt the intrinsic instability of quasi-steady-state photorefractive self-trapping, driving beam evolution into a stable oscillating two-soliton-state configuration. (C) 2000 Optical Society of America OCIS codes: 190.5330, 230.3090.

1999
G Bitton, AJ Agranat, and VM Fridkin. 1999. “The Bulk Photovoltaic effect in Photorefractive KLTN Crystals.” Ferroelectric Letters , 25, 1-2, Pp. 1-9. Abstract
Experimental evidence of the bulk photovoltaic effect in photorefractive K1-xLixTa1-xNbyO3 (KLTN) crystals is shown. The dependence of the bulk photovoltaic effect on the pbotorefractive impurities type is presented. The current voltage characteristic is presented for different temperatures. It was found that, in Fe-doped KLTN crystals at low temperature, the bulk photovoltaic effect is the dominant transport mechanism contributing to the photorefractive process.
O Levi, S Shalom, I Benjamin, G Perepelitsa, AJ Agranat, R Neumann, Y Avny, and D Davidov. 1999. “Conjugated polymeric composites for holographic storage.” Synthetic Metals , 102, Pp. 1178-1181. Abstract
We report here on the fabrication and optimization of composites of conjugated polymer in Sol-Gel and PVA matrices. FTIR spectroscopy as well as other observations show that efficient phase and absorption holograms can be created in the material upon illumination, via the photochromic effect. The main contribution to the absorption change is chain scission and photo-oxidation mechanism. Optimized holographic composites with diffraction efficiencies as high as 26% are shown. Beam interaction between the writing beams is observed for these composites, while the diffraction efficiencies was improved by an order of magnitude.
B Crosignani, A Degasperis, E DelRe, P Di Porto, and AJ Agranat. 1999. “Nonlinear optical diffraction effects and solitons due to anisotropic charge-diffusion-based self-interaction.” Physics Review 82 (8), Pp. 1664 - 1667. Publisher's Version Abstract

We report the first observation of self-modified optical diffraction, beam ellipticity recovery and conservation, and intensity independent self-focusing in an anisotropic diffusion-type nonlinearity realized in ferroelectrics heated above the centrosymmetric transition. The interaction, a photorefractive diffusion-driven quadratic nonlinearity, constitutes the first known natural realization of a higher-order logarithmic nonlinearity and allows an analytical description of the observed phenomena and the prediction of a class of noncircular solitons with no characteristic length scale.

E DelRe, M Tamburrini, M Segev, R Della Pergola, and AJ Agranat. 1999. “Spontaneous self-trapping of optical beams in metastable paraelectric crystals.” Physics Review Letters 83 (10), Pp. 1954 - 1957. Publisher's Version Abstract

We report on the observation of a new mechanism for self-trapping of optical beams: self-trapping that stems from spontaneous creation of ferroelectric crystalline clusters, seeded by a weak photorefractive diffusion field. This is an evident observation of the highly nonlinear aspects of propagation in a thermodynamically metastable system, including optically driven crystalline ordering in a medium undergoing a phase transition.

1998
O Levi, G Perepelitsa, D Davidov, AJ Agranat, I Benjamin, S Shalom, R Neumann, and Y Avny. 1998. “Holographic Storage in Conjugated Polymers Composites.” Phys. Rev. B Rapid Comm., 57, Pp. 12647-12650. Abstract
We report here on the fabrication and optimization of composites of conjugated polymer in Sol-Gel and PVA matrices. FTIR spectroscopy as well as other observations show that efficient phase and absorption holograms can be created in the material upon illumination, via the photochromic effect. The main contribution to the absorption change is chain scission and photo-oxidation mechanism. Optimized holographic composites with diffraction efficiencies as high as 26% are shown. Beam interaction between the writing beams is observed for these composites, while the diffraction efficiencies was improved by an order of magnitude.
E DelRe, B Crosignani, M Tamburrini, M Segev, M Mitchell, E Refaeli, and AJ Agranat. 1998. “One-dimensional steady-state photorefractive spatial solitons in centrosymmetric paraelectric potassium lithium tantalate niobate.” Optics Letters 23 (6), Pp. 421 - 423. Publisher's Version Abstract

We report the first observation of spatial one-dimensional photorefractive screening solitons in centrosymmetric media and compare the experimental results with recent theoretical predictions. We find good qualitative agreement with theory. (C) 1998 Optical Society of America.

M Balberg, M Razvag, E Refaeli, and AJ Agranat. 1998. “Electric field multiplexing of volume hologram in paraelectric crystals.” Applied Optics , 37, Pp. 841-847. Abstract
Electric-field multiplexing (EFM) results from the tuning of the effective wavelength of the light beam inside a photorefractive crystal. This tuning results from the application of an external electric field to the crystal during holographic recording. We demonstrate the high Bragg selectivity of this multiplexing technique in paraelectric crystals and compare it with the selectivity obtained in the ferroelectric phase. The effects of the two major physical parameters of working in the paraelectric phase, the temperature and the external electric field applied during the writing stage, are investigated. Experimental results of the EFM of three image-bearing holograms recorded in reflection geometry are presented along with a qualitative analysis of the Bragg selectivity in paraelectric crystals.
G Bitton, M Razvag, and Aharon J Agranat. 1998. “Formation of Metastable Ferroelectric Clusters in K1-XLiXTa1-YNbYO3:Cu, V at the Paraelectric Phase.” Phys. Rev. B , 58, 9, Pp. 5282-5286.
B Pessach, Eli Refaeli, and Aharon J Agranat. 1998. “Investigation of the holographic storage capacity of paraelectric KLTN.” Optics Letters , 23, 4/15, Pp. 642-644.
Eugenio DelRe, Mario Tamburrini, Mordechai Segev, Eli Refaeli, and Aharon J Agranat. 1998. “Two-dimensional photorefractive spatial solitons in centrosymmetric paraelectric potassium–lithium–tantalate–niobate..” Applied Physics Letters, 73, 1. Publisher's Version Abstract

We report the observation of steady-state two-dimensional photorefractive self-trapping and screening spatial soliton formation in a sample of potassium–lithium–tantalate–niobate in the centrosymmetric paraelectric phase. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]Copyright of Applied Physics Letters is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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1997
Xiaolin Tong, Min Zhang, Amnon Yariv, and Aharon J Agranat. 1997. “Copper, hydrogen, and titanium incorporation in potassium lithium tantalate niobate single crystals..” Applied Physics Letters, 70, 13, Pp. 1688. Publisher's Version Abstract
Analyzes the model proposed for the diffusion of copper, hydrogen and titanium through potassium lithium tantalate niobate crystals. Occupation of potassium/lithium vacant sites by copper and hydrogen ions; Effect of titanium on the ability of hydrogen ions to stay at the sites; Reduction in the hydrogen ion concentration.
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