Publications

2012
Jacopo Parravicini, Claudio Conti, Aharon J Agranat, and Eugenio DelRe. 2012. “Programming scale-free optics in disordered ferroelectrics..” Optics Letters, 37, 12, Pp. 2355 - 2357. Publisher's Version Abstract

Using the history dependence of a dipolar glass hosted in a compositionally disordered lithium-enriched potassium tantalate niobate (KTN:Li) crystal, we demonstrate scale-free optical propagation at tunable temperatures. The operating equilibration temperature is determined by previous crystal spiralling in the temperature/cooling-rate phase space.;

Accession Number: 22739906. Language: English. Date Created: 20120628. Date Completed: 20130117. Update Code: 20141125. Publication Type: Journal Article. Journal ID: 7708433. Publication Model: Print. Cited Medium: Internet. NLM ISO Abbr: Opt Lett. Linking ISSN: 01469592. Subset: PubMed-not-MEDLINE; Date of Electronic Publication: 20120615. ; Original Imprints: Publication: New York, Optical Society of America.

J Parravicini, C Conti, AJ Agranat, and E DelRe. 2012. “Rejuvenation in scale-free optics and enhanced diffraction cancellation life-time.” Optics Express 20 (24), Pp. 27382 - 27387. Publisher's Version Abstract

We demonstrate rejuvenation in scale-free optical propagation. The phenomenon is caused by the non-ergodic relaxation of the dipolar glass that mediates the photorefractive nonlinearity in compositionally-disordered lithium-enriched potassium-tantalate-niobate (KTN:Li). We implement rejuvenation to halt aging in the dipolar glass and extend the duration of beam diffraction cancellation. (C) 2012 Optical Society of America

E Safrai, P Ben Ishai, A Caduff, A Puzenko, A Polsman, AJ Agranat, and Y Feldman. 2012. “The remote sensing of mental stress from the electromagnetic reflection coefficient of human skin in the sub-THz range.” Bioelectromagnetics 33 (5), Pp. 375 - 382. Publisher's Version Abstract
Recent work has demonstrated that the reflection coefficient of human skin in the frequency range from 95 to 110?GHz (W band) mirrors the temporal relaxation of stress induced by physical exercise. In this work, we extend these findings to show that in the event of a subtle trigger to stress, such as mental activity, a similar picture of response emerges. Furthermore, the findings are extended to cover not only the W band (75-110?GHz), but also the frequency band from 110 to 170?GHz (D band). We demonstrate that mental stress, induced by the Stroop effect and recorded by the galvanic skin response (GSR), can be correlated to the reflection coefficient in the aforementioned frequency bands. Intriguingly, a light physical stress caused by repeated hand gripping clearly showed an elevated stress level in the GSR signal, but was largely unnoted in the reflection coefficient in the D band. The implication of this observation requires further validation. Bioelectromagnetics 33:375382, 2012. (C) 2011 Wiley Periodicals, Inc.
2011
J Parravicini, F Di Mei, C Conti, AJ Agranat, and E DelRe. 2011. “Diffraction cancellation over multiple wavelengths in photorefractive dipolar glasses.” Optics Express 19 (24), Pp. 24109 - 24114. Publisher's Version Abstract

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

Heli Siman-Tov, Alexander Gumennik, Harel Ilan, Noa Mazursky, and Aharon J Agranat. 2011. “Construction of conducting and photoconducting 3D structures with submicron resolution in electrooptical substrates.” Applied Physics A - Materials Science & Processing , 102, 1, Pp. 45-48. Publisher's Version Abstract
It is shown that the implantation of protons in electrooptical substrates enables the construction of 3D structures with submicron features that are both conductive and photoconductive embedded in amorphized regions that possess reduced refractive index. The conductivity and photoconductivity are attributed to the transformation of the material into a degenerate semiconductor due to the formation of high concentration of OH.sup.- complexes that are created by the bonding of the implanted H.sup.+ ions to the O.sup.-2 ions of the lattice. It is argued that these results extend significantly the capabilities of integrated photonic circuits and devices fabricated by Refractive Index Engineering by ion implantations.
Item Citation: Applied Physics A: Materials Science & Processing. Jan 2011, Vol. 102 Issue 1, p45, 4 p.Accession Number: edsgcl.246178061; Publication Type: Academic Journal; Source: Applied Physics A: Materials Science & Processing; Language: English; Publication Date: 20110101; Rights: Copyright 2011 Gale, Cengage Learning. All rights reserved., COPYRIGHT 2011 Springer; Imprint: Springer
A Gumennik, Y Kurzweil-Segev, and AJ Agranat. 2011. “Electrooptical effects in glass forming liquids of dipolar nano-clusters embedded in a paraelectric environment.” Optical Materials Express, 1, 5, Pp. 803-815. Abstract
Studies of the electrooptic effect in potassium tantalate niobate (KTN) and Li doped KTN in the vicinity of the ferroelectric phase transition are reported. It was observed that in KTN the standard electrooptic behavior is accompanied by electrically induced depolarization of the light traversing through the crystal. This behavior is attributed to the influence of the fluctuating dipolar clusters that are formed in KTN above the ferroelectric phase transition due to the emergence of the Nb ions out of the center of inversion of the unit cell. It was shown in addition that this behavior is inhibited in Li doped KTN, which enables exploiting the large electrooptic effect in these crystals.
E DelRe, E Spinozzi, AJ Agranat, and C Conti. 2011. “Scale-free optics and diffractionless waves in nanodisordered ferroelectrics..” Nature Photonics, 5, 1, Pp. 39. Publisher's Version Abstract

Wavelength rigidly fixes the diffraction that distorts waves during propagation, and poses fundamental limits to imaging, microscopy and communication. This distortion can be avoided by using waveguides or nonlinearity to produce solitons. In both cases, however, diffraction is only compensated, so the wavelength still imposes rigid laws on wave shape, size and soliton intensity. Nonlinearity, in turn, can introduce new spatial scales. In principle, if one is able to identify a nonlinearity that introduces an intensity-independent scale that cancels the wavelength, 'scale-free' propagation can occur. In this regime, diffraction ceases, and waveforms will naturally propagate without distortion, forming solitons of any size and intensity, even arbitrarily low. Here we provide the first experimental evidence of scale-free optical propagation in supercooled copper-doped KTN:Li, a recently developed out-of-equilibrium ferroelectric. This demonstrates that diffraction can be cancelled, and not merely compensated, thus leading to a completely new paradigm for ultraresolved imaging and microscopy. [ABSTRACT FROM AUTHOR]Copyright of Nature Photonics is the property of Nature Publishing Group 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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C Conti, AJ Agranat, and E DelRe. 2011. “Subwavelength optical spatial solitons and three-dimensional localization in disordered ferroelectrics: Toward metamaterials of nonlinear origin..” Physical Review A: Atomic, Molecular & Optical Physics, 84, 4-B, Pp. 043809-1 - 043809-4. Publisher's Version Abstract

We predict the existence of a class of multidimensional light localizations in out-of-equilibrium ferroelectric crystals. In two dimensions, the nondiffracting beams form at an arbitrary low-power level and propagate even when their width is well below the optical wavelength. In three dimensions, a subwavelength light bullet is found. The effects emerge when compositionally disordered crystals are brought to their metastable glassy state, and leading to the suppression of evanescent waves, they can have a profound impact on super-resolved imaging and ultradense optical storage, resembling metamaterials in many ways. [ABSTRACT FROM AUTHOR]Copyright of Physical Review A: Atomic, Molecular & Optical Physics is the property of American Physical Society 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.)

Accession Number: 70317274; Conti, C. 1,2 Agranat, A. J. 3 DelRe, E. 4; Affiliation: 1: Department of Molecular Medicine, University Sapienza, Viale Regina Elena, 324, I-00161 Rome, Italy 2: Institute for Complex Systems - CNR, Department of Physics, University Sapienza, Piazzale Aldo Moro 2, I-00187 Rome, Italy 3: Applied Physics Department, Hebrew University of Jerusalem, IL-91904, Israel 4: Dipartimento di Ingegneria Elettrica e dell'Informazione, Universita' dell'Aquila, I-67100 L'Aquila, Italy; Source Info: Oct2011, Vol. 84 Issue 4-B, p043809-1; Subject Term: METAMATERIALS; Subject Term: FERROELECTRIC crystals; Subject Term: SOLITONS; Subject Term: WAVELENGTHS; Subject Term: OPTICAL disk drives; Subject Term: IMAGING systems; NAICS/Industry Codes: 334110 Computer and peripheral equipment manufacturing; NAICS/Industry Codes: 334112 Computer Storage Device Manufacturing; Number of Pages: 4p; Document Type: Article

2009
A Pierangelo, A Ciattoni, E Palange, AJ Agranat, and E DelRe. 2009. “Electro-activation and electro-morphing of photorefractive funnel waveguides.” Optics Express 17 (25), Pp. 22659 - 22665. Publisher's Version Abstract

We demonstrate the electro-activation of funnel waveguides through the quadratic electro-optic effect in paraelectric potassium-lithium-tantalate- niobate. This allows us to achieve electro-optic intensity modulation in a single optical beam, a 1x2 switch, and finally the electrically controlled morphing of a single waveguide into a 1x2 and a 1x4 divider. (C) 2009 Optical Society of America

Y Feldman, A Puzenko, P Ben Ishai, A Caduff, I Davidovich, F Sakran, and AJ Agranat. 2009. “The electromagnetic response of human skin in the millimetre and submillimetre wave range.” Physics in Medicine and Biology, 54, 11, Pp. 3341-3363. Publisher's Version
Accession Number: edselc.2-52.0-69249232347; (Physics in Medicine and Biology, 2009, 54(11):3341-3363) Publication Type: Academic Journal; Rights: Copyright 2010 Elsevier B.V., All rights reserved.
N Sapiens, A Weissbrod, and AJ Agranat. 2009. “Fast Electroholographic Switching.” Optics Letters , 34, 3, Pp. 353-355 . Abstract
Electroholographic switching with a rise time of 13 ns is henceforth presented. The switching was demonstrated in a potassium lithium tantalate crystal doped with copper and titanium with Tc=10 degrees C. The crystal was operated at 17 degrees C. The switching operation was done in the g11/g12 configuration, in which the Bragg condition remains fulfilled at all levels of the applied field. As electroholography is a wavelength-selective switching method, this opens the way for implementing optical packet switching and fast wavelength addressing schemes in optical fiber networks that apply wavelength division multiplexing.
A Gumennik, G Perepelitsa, A Israel, and AJ Agranat. 2009. “A tunable channel waveguide array fabricated by the implantations of Heions in an electrooptical KLTN substrate.” Optics Express, 17, 8, Pp. 5919-6251. Abstract
An electrooptical channel waveguide array was constructed in potassium lithium tantalate niobate substrate by the implantation of He+ ions at high energies. The array was fabricated by two successive implantation sessions at 1.6 MeV and 1.2 MeV through a comb-like stopping mask that limited the implanted ions to penetrate the substrate in 1 ?m wide stripes periodically distributed at 3.5 ?m intervals. This generated a grating of amorphized stripes with reduced refractive index. This was followed by a uniform implantation of He+ ions at 1.8 MeV which created a bottom cladding layer below the array. Wave propagation in the array was studied by focusing a light beam at 636 nm into the central channel, and observing the wavefront it created at the output plane of the array. It was found that applying an electric field across the array strongly affects the coupling between adjacent channels and governs the width of the wavefront at the output plane.
2008
Y Feldman, A Puzenko, P Ben Ishai, A Caduff, and AJ Agranat. 2008. “Human skin as arrays of helical antennas in the millimeter and submillimeter wave range.” Physical Review Letters, 100, 12. Publisher's Version
Accession Number: edselc.2-52.0-41549168686; (Physical Review Letters, 27 March 2008, 100(12)) Publication Type: Academic Journal; Rights: Copyright 2008 Elsevier B.V., All rights reserved.
A Pierangelo, E DelRe, E Palange, A Ciattoni, B ) Crosignani, and AJ Agranat. 2008. “Linear writing of waveguides in bulk photorefractive crystals through a two-step polarization sequence.” Journal of Optics A: Pure and Applied Optics, 10, 6. Publisher's Version

Accession Number: edselc.2-52.0-44449142523; (Journal of Optics A: Pure and Applied Optics, 1 June 2008, 10(6)) Publication Type: Academic Journal; Rights: Copyright 2013 Elsevier B.V., All rights reserved.

Harel Ilan, Alexander Gumennik, Galina Perepelitsa, Abraham Israel, and Aharon J Agranat. 2008. “Construction of an optical wire imprinted in potassium lithium tantalate niobate by He+ implantation..” Applied Physics Letters, 92, 19, Pp. 192101. Publisher's Version Abstract
A channel waveguide constructed in potassium lithium tantalate niobate (KLTN) substrate by the implantation of He+ ions at 1.65 MeV is presented. The waveguide has a trapezoidal profile with a crystalline KLTN core surrounded by amorphized KLTN created by the implantation. The implantation was done through a 2 μm thick gold stopping mask with a trapezoidal groove. During the implantation, the contour of the groove was replicated beneath the surface of the substrate forming the trapezoidal cladding of the channel waveguide. The channel waveguide is designed as the interconnecting element in electro-optical integrated circuits. [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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A D'Ercole, A Pierangelo, E Palange, A Ciattoni, AJ Agranat, and E DelRe. 2008. “Photorefractive solitons of arbitrary and controllable linear polarization determined by the local bias field.” Optics Express 16 (16), Pp. 12002 - 12007. Publisher's Version Abstract

We discuss and experimentally demonstrate a scheme to achieve photorefractive solitons of arbitrary linear polarization using the quadratic electro-optic effect and describe the observation of the self-trapping of a set of linear polarized beams in different positions of a paraelectric photorefractive crystal of potassium-lithium-tantalate-niobate (KLTN) biased by the inhomogeneous field produced by two miniaturized top electrodes. The polarization of the single solitons of the set is determined by the local electrostatic configuration and the underlying tunable anisotropy, which is detected through zero-field electro-activation. (C) 2008 Optical Society of America.

2007
E DelRe, A Pierangelo, E Palange, A Ciattoni, and AJ Agranat. 2007. “Beam shaping and effective guiding in the bulk of photorefractive crystals through linear beam dynamics..” Applied Physics Letters, 91, 8, Pp. 081105. Publisher's Version Abstract
The authors demonstrate a technique to optically imprint through linear beam propagation an index pattern in the bulk of a photorefractive crystal capable of beam reshaping and waveguiding. The procedure is based on the separation into two distinct phases of the photosensitive and refractive response, so that light is in all cases undergoing only linear propagation. When saturation in the response becomes dominant, the scheme is able to achieve both one-dimensional and two-dimensional waveguiding. The result allows the straightforward writing of multiwaveguide circuits, where traditional schemes based on spatial solitons are in practice burdened by nonlinearity. [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.)
Accession Number: 27758753; DelRe, E. 1 Pierangelo, A. 1 Palange, E. 1 Ciattoni, A. 2 Agranat, A. J. 3; Affiliation: 1: Laboratorio di Ottica e Fotonica, Dipartimento di Ingegneria Elettrica e dell’Informazione, Università dell’Aquila, 67040 L’Aquila, Italy 2: Laboratorio Regionale CASTI, INFM-CNR, Dipartimento di Fisica, Università dell’Aquila, 67010 L’Aquila, Italy 3: Department of Applied Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel; Source Info: 8/20/2007, Vol. 91 Issue 8, p081105; Subject Term: PHOTOREFRACTIVE materials; Subject Term: CRYSTALS; Subject Term: WAVEGUIDES; Subject Term: NONLINEAR optics; Subject Term: BEAM dynamics; Number of Pages: 3p; Illustrations: 1 Diagram, 2 Graphs; Document Type: Article
Alexander Gumennik, Har'el Ilan, Roei Fathei, Abraham Israel, Aharon J Agranat, Igal Shachar, and Michael Hass. 2007. “Design methodology of refractive index engineering by implantation of high-energy particles in electro-optic materials.” Applied Optics , 46, 19, Pp. 4132-7. Publisher's Version Abstract
Slab waveguides were constructed in [K.sub.1-x]-[Li.sub.x][Ta.sub.1-y] [Nb.sub.y][O.sub.3] crystals by the implantation of [sup.12][C.sup.+4] ions at 30 MeV and [sup.16][O.sup.+5] ions at 30 and 40 MeV. The waveguides were characterized by a prism coupler setup. A refractive index drop of 10.9% was observed in a layer formed by the implantation of [sup.16][O.sup.+5] ions at 30 MeV. The carbon-implanted waveguides were found to be thermally stable after annealing at 450 [degrees]C. A semiempirical formula for predicting the change in the refractive index given the parameters of the implantation process was developed. It is argued that the combination of the basic implantation process with the semiempirical formula can be developed to become a generic method for constructing complex electro-optic circuits with a wave-guided architecture. OCIS codes: 160.2260, 230.7400, 220.4000, 130.3120, 350.4600.
Item Citation: Applied Optics. July 1, 2007, Vol. 46 Issue 19, p4132, 6 p.Accession Number: edsgcl.165971006; Publication Type: Academic Journal; Source: Applied Optics; Language: English; Publication Date: 20070701; Rights: Copyright 2007 Gale, Cengage Learning. All rights reserved., COPYRIGHT 2007 Optical Society of America; Imprint: Optical Society of America
AJ Agranat, CEM de Oliveira, and G Orr. 2007. “Dielectric Electrooptic Gratings in Potassium Lithium Tantalate Niobate.” J. of Non-Cryst. Solids, 353, 47-51, Pp. 4405-4410. Abstract
Volume phase gratings have been fabricated by controlled generation of periodic striations during the growth of copper doped potassium lithium tantalate niobate crystals. Gratings with periods ranging from below 1 to 5 μm were fabricated. It is shown that the fabricated composition grating induces a refractive index grating which is a superposition of a fixed grating and an electrically controlled (electrooptic) grating. The electrooptic grating is produced due to the generation of a spatial modulation of the Curie temperature which is manifested as a correlated modulation of the static dielectric constant. It was also observed that when operated at the immediate vicinity of the phase transition temperature the diffraction efficiency from these gratings was bi-stable at a specific electric field due to an induced shift of the Curie temperature.
SE Lerner, P Ben Ishai, AJ Agranat, and Y Feldman. 2007. “Percolation of polar nanoregions: A dynamic approach to the ferroelectric phase transition.” J. of Non-Cryst. Solids 353 (47-51), Pp. 4422 - 4427. Publisher's Version Abstract
The percolative nature of the ferroelectric phase transition in a potassium tantalate niobate (KTN) crystal is studied using time domain dielectric spectroscopy. A relaxation process linked to the off-center niobium ions is observed. The dynamic nature of this relaxation shows well defined temperature regimes in which it progresses from independent (Arrhenius) to cooperative (Vogel-Fulcher-Tammann) behavior. A recursive fractal model was applied in order to interpret the data obtained from the dielectric measurements. The structural parameters, nu and mu, derived from the correlation functions, enable the investigation of the onset of the phase transition in terms of the fractal dimensions of the polarization excitation. (c) 2007 Elsevier B.V. All rights reserved.

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