Search

Refereed/Peer-reviewed The generation of Mn4+ in α-Al2O3:Mn3+ by soft X-ray exposure is demonstrated with a large dynamic range of the X-ray generated Mn4+ luminescence signal, indicating the potential use of α-Al2O3:Mn3+ for multilevel optical data storage. Samples with a range of Mn concentrations (0.05, 0.1, 0.2, 0.4, 0.6 and 1.2 atom%) were prepared via a facile combustion method and the sample with 0.4 atom% was found to display the highest luminescence intensity. The stored information can be read out via the R-lines (2E -> 4A2) under ∼470 nm (4A2 -> 4T2), or ∼630 nm (4A2 -> 2T1) excitation with the latter being preferred since photobleaching is minimized. Interestingly, the Mn4+ valence state can be fully switched back to Mn3+ by blue light exposure (e.g., 462 nm laser diode). The stored information could be repeatedly written and erased, showing no significant deterioration over five consecutive cycles, with less than 5% uncertainty.

Transparent glass has been identified as a vital medium for three-dimensional (3D) optical information storage and multi-level encryption. However, it has remained a challenge for directly writing 3D patterning inside a transparent glass using semiconductor blue laser instead of high-cost femtosecond laser. Here, we demonstrate that rare earth ions doped transparent glass can be used as 3D optical information storage and data encryption medium based on their reversible transmittance and photoluminescence manipulation. The color of tungsten phosphate glass doped with rare earth ions change reversibly from light yellow to blue upon alternating 473 nm laser illumination and temperature stimulation, resulting in the reversible luminescence modulation. The information data could be repeatedly written and erased in arbitrary 3D space of transparent glass, not only showing the ability of the excellent reproducibility and storage capacity, but also opening opportunities in information security. The present work expands the application fields of luminescent glass, and it is conducive to develop a novel 3D data storage and information encryption media., Three-dimensional (3D) optical information can be written in transparent glass using a focused 473 nm laser beam, which will be read by photo-modulation.

Although photonics presents the fastest and most energy-efficient method of data transfer, magnetism still offers the cheapest and most natural way to store data. The ultrafast and energy-efficient optical control of magnetism is presently a missing technological link that prevents us from reaching the next evolution in information processing. The discovery of all-optical magnetization reversal in GdFeCo with the help of 100 fs laser pulses has further aroused intense interest in this compelling problem. Although the applicability of this approach to high-speed data processing depends vitally on the maximum repetition rate of the switching, the latter remains virtually unknown. Here we experimentally unveil the ultimate frequency of repetitive all-optical magnetization reversal through time-resolved studies of the dual-shot magnetization dynamics in Gd27Fe63.87Co9.13. Varying the intensities of the shots and the shot-to-shot separation, we reveal the conditions for ultrafast writing and the fastest possible restoration of magnetic bits. It is shown that although magnetic writing launched by the first shot is completed after 100 ps, a reliable rewriting of the bit by the second shot requires separating the shots by at least 300 ps. Using two shots partially overlapping in space and minimally separated by 300 ps, we demonstrate an approach for GHz magnetic writing that can be scaled down to sizes below the diffraction limit., Optical magnetization: extreme limits for magnetic data recording with light The potential for combining the speed of photonics with the advantages of magnetic data storage, using pulsed laser light to control the magnetization of alloys of gadolinium, iron and cobalt (GdFeCo), has been explored and quantified. Achieving ultrafast and energy-efficient optical control of magnetism could revolutionize information-processing technology. Researchers led by Xiangping Li at Jinan University in China and Alexey V. Kimel at Radboud University in The Netherlands have experimentally determined the fastest possible rate of the optical reversal of magnetization achieved by this promising new technology. They suggest data switching repetition rates of up to three billion cycles per second (3 GHz) are feasible. They also propose a method to achieve spatial resolution of data recording at scales below light’s ‘diffraction limit’, which is generally believed to restrict the attainable resolution.

The launch of the big data era puts forward challenges for information preservation technology, both in storage capacity and security. Herein, a brand new optical storage medium, transparent glass ceramic (TGC) embedded with photostimulated LiGa5O8: Mn2+ nanocrystals, capable of achieving bit-by-bit optical data write-in and read-out in a photon trapping/detrapping mode, is developed. The highly ordered nanostructure enables light–matter interaction with high encoding/decoding resolution and low bit error rate. Importantly, going beyond traditional 2D optical storage, the high transparency of the studied bulk medium makes 3D volumetric optical data storage (ODS) possible, which brings about the merits of expanded storage capacity and improved information security. Demonstration application confirmed the erasable–rewritable 3D storage of binary data and display items in TGC with intensity/wavelength multiplexing. The present work highlights a great leap in photostimulated material for ODS application and hopefully stimulates the development of new multi-dimensional ODS media., Optics: Next generation of optical data storage systems An optical data storage (ODS) system that is cost-effective to make and easily scalable could lay the foundations for data storage technologies with higher capacity and improved security. The era of big data is driving the need for data storage systems with larger capacity, better security and improved performance. However, even the latest two-dimensional optical disk technologies cannot store more than one terabyte of data, leading scientists to explore alternative technologies. Now, a team of Chinese researchers, led by Yuansheng Wang from the Chinese Academy of Sciences, has developed a three-dimensional ODS system that uses light-emitting nanocrystals (NCs) to store and retrieve information. Made from a transparent glass ceramic embedded with photostimulated luminescent rare-earth-doped metallic NCs, the new ODS system can store 3D optical data with increased capacity and improved security compared with current technologies.

Optical contrast formation by Ga+ ion implantation has been made use of for focused ion beam (FIB) writing of nano-scale optical patterns in tetrahedral amorphous carbon (ta-C). Initial UV-VIS optical spectroscopy results with Ga+ broad-beam ion implantation have shown well expressed ion beam induced photo-darkening effect in thin ta-C films. It is manifested by a significant shift of the optical absorption edge to lower photon energies as obtained from optical transmission measurements of ta-C samples, implanted with Ga+ at ion energy E = 20 keV and ion fluences D = 3e14 and 3e15 cm-2. This shift is accompanied by a considerable increase of the absorption coefficient (photo-darkening effect) in the measured photon energy range (0.5÷3.0 eV). The obtained optical contrast (between implanted and unimplanted film material) could be made use of in the area of high-density optical data storage using focused Ga+ ion beams. The underlying structural modifications, induced by the Ga+ ion bombardment, have been investigated by x-ray photo-electron spectroscopy (XPS), transmission (TEM) and scanning (SEM) electron microscopy measurements. Focused ion beam (FIB) implanted patterns in ta-C samples, obtained with a fluence of 5e15 cm-2, are also presented.

In this paper, we study the wear resistance of multi-layered composites of Cu/SiC + Gr hybrid composites prepared by layer compaction and pressure sintering. The tribological behavior and wear resistance of the composites were evaluated at a range of sliding speeds (5, 10, 30 and 35m/s) in a laboratory scale inertia brake dynamometer for brake friction material applications. The wear surface morphology and mechanisms were studied using scanning electron microscopy (SEM), XRD, and stereoscopy. The microstructure of the composites was also characterized using SEM and optical microscopy and the mechanical response in compression and flexure was evaluated. The results of these tests indicate that the density, wear resistance, braking behavior and mechanical response can be significantly improved by the presence of a layer of copper away from the sliding surface. The presence of the layer also improved friction and wear resistance significantly. The formation of mechanically mixed tribolayer and oxides (Fe3O4) reduced the wear rate and stabilized the friction coefficient at 30 and 35m/s. Finally, crack deflection and branching at the interface between the composite and Cu layers improved the flexural strength of the layered composites. The fractography analysis indicates a quasi-cleavage intergranular fracture in the composite layer and a purely ductile fracture in the Cu layer. � 2014 Elsevier B.V.

The effect of nucleation and plasticization on the stereocomplex formation between poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) was investigated in blends where PDLA is added as a minor phase in a major phase of PLLA. The use of small amounts of PDLA is aimed at creating a high melting point stereocomplex phase that in turn can serve as nucleating agent for the major phase of PLLA. Blends containing 5% PDLA with talc or organic phosphonate as nucleants and polyethylene glycol as plasticizer were prepared via melt-blending. Their crystallization behavior was investigated through Differential Scanning Calorimetry (DSC) using various thermal histories. Two peculiar stereocomplex melting endotherms were found. The peak temperature and enthalpy of these two endotherms were correlated to prior isothermal crystallization temperature. The different endotherms were also associated with two different crystalline morphologies observed by optical microscopy and referred to as Network and Spherulitic morphologies. The influence of plasticization and of heterogeneous nucleation on these morphologies was investigated through optical microscopy and calorimetric observations. © 2013 Elsevier Ltd. All rights reserved.

Measurements of the internal geometry of a carbon fiber non-crimp 3D orthogonal woven composite are presented, including: waviness of the yarns, cross sections of the yarns, dimensions of the yarn cross sections, and local fiber volume fraction. The measured waviness of warp and fill yarns are well below 0.1%, which shows that the fabric termed here “non-crimp” has nearly straight in-plane fibers as-produced, and this feature is maintained after going through all steps of fabric handling and composite manufacturing. The variability of dimensions of the yarns is in the range of 4–8% for warp and fill directions, while the variability of the yarn spacing is in the range of 3–4%. These variability parameters are lower than respective ranges of variability of the yarn waviness and the cross-sectional dimensions in typical carbon 2D weave and 3D interlock weave composites, which are also illustrated in this work for comparison.

In this paper, we have investigated a remote encoding/decoding method of micrometer-sized multibit magnetic tags and demonstrated the operation of magnetic digital tags to discuss the practical issues which arise. The tags are formed from micron scale patterned ferromagnetic Co thin films, which are engineered to have different switching fields by tailoring the geometric shape of the elements. This enables the tags to be encoded and read by a sequence of globally applied magnetic fields. Full-field magneto-optical microscopy was used to achieve the remote writing and reading for magnetic digital tags. Our results demonstrate that the elements in the multibit tags are well separated in switching field and can be encoded/decoded independently by using globally applied magnetic fields and magneto-optical microscopy. We will discuss practical issues for high-information multibit magnetic tags including switching field distribution and repeatability with implications for the field of bioassays. © 2009 IEEE. 45 6 2878 2881 Cited By :2

International audience; Optical data storage was performed with various thin polymer films containing coumarin-based derivatives and by using femtosecond laser pulses as well as two-photon absorption processes. Exploring the photodimerization attribute of coumarin derivatives and using appropriate irradiation wavelengths, recording/erasing processes could be carried out in the same area. Second harmonic generation microscopy was used to read the stored information.

Photopolymers present appealing optical properties for holographic and diffractive applications. They enable modulation of the electrical permittivity and thickness and are self-processing, and layers with a wide range of thicknesses and properties can be fabricated on demand. In order to obtain a complete characterization of the material, low spatial frequency analysis has become a fundamental tool because the motion of the components inside of the material can be measured. We propose to use an index matching component to carry out a complete characterization and to differentiate the “apparent” and the real monomer diffusion. We also have quantified the minimum thickness to obtain the phase modulation of 2𝜋 required for the fabrication of many diffractive elements such as lenses, axicons, or blazed gratings. Finally, we have studied the influence of the thermal effects in the thickness variations. The work was supported by the “Ministerio de Economía y Competitividad” of Spain under projects FIS2011-29803-C02-01 and FIS2011-29803-C02-02 and by the “Generalitat Valenciana” of Spain under projects PROMETEO/2011/021 and ISIC/2012/013.

Thin films (d∼200 nm) of hydrogenated amorphous silicon carbide (a-SiC:H), deposited by RF reactive magnetron sputtering, have been ion implanted with high doses (D=1016–1017 cm−2) of Ga+ as the implant species. The increased disorder and additional structural modification of a-SiC:H, induced by the implantation of Ga+, results in a considerable change of the optical properties, best manifested by a significant shift of the optical absorption edge to lower photon energies in the results obtained by optical transmission and reflection measurements and as derived from photo-thermal-deflection spectroscopy results. This shift may be attributed both to additional defect introduction and to accompanying structural modification effects, as confirmed by optical absorption measurements in the infra-red region and by Raman spectroscopy results.

We report on the highly efficient generation of stable Sm²⁺ in nanocrystalline BaFCl:Sm³⁺ by exposure in the deep UV (UV-C) below 250 nm. The generated Sm²⁺ can be read out via its distinct fluorescence signature which is efficiently excited around 425 nm by the relatively strong f-d transitions with ε ≈400 (l mol-1 cm-1). The generation of Sm²⁺ can also be reversed, erasing the fluorescence signal via two-photon ionization by increasing the power at 425 nm from ≤ 1 mW/cm2 to ~100 mW/cm2. It follows that the switching mechanism is based on oxygen impurities that are in close proximity to the Sm³⁺ ions. The photoionization kinetics indicate that the average Sm³+- oxide impurity separation is a few interionic spacings. The level of Sm³⁺- Sm²⁺ conversion in BaFCl is shown to be tunable over a large dynamic range, and therefore could serve as a platform for rewritable ultra-high density multi-level optical data storage. The present study also sheds light on BaFCl:Sm³⁺ as a photoluminescent X-ray storage phosphor. Refereed/Peer-reviewed

Spots of second harmonic generation (SHG) are produced from nanopatterned sub-micrometer areas of nonlinear polymer media. Information is written by using a biased-AFM tip, a highly nonlinear polymer (poly(methyl metha-acrylate)-co-Disperse Red 1), and a novel "floating-tip nanolithography" (FTN) technique. Dipoles are oriented and aligned at the nanoscale under the biased-AFM tip, resulting in SHG production. The information is storable over weeks.

International audience; We show both numerically and experimentally that intense, narrow, and low-divergence beams of light are produced at the apex of dielectric pyramid-shaped microtips. These beams exhibit a Bessel transverse profile but are narrower than the usual Bessel beam, allowing for a significant enhancement of the light intensity inside the beam. They are generated by axicon-like structures with submicrometric height imprinted in glass by combining optical lithography and chemical etching. The resulting beams are experimentally imaged using fluorescence microscopy, in remarkable agreement with numerical computations.

The comparison between four different photopolymers is presented. The direct parameters determination as optical recording media is carried out using the zero spatial frequency limit. The bahavior of coverplated and uncoverplated material layers is analyzed. We have substituted Acrylamide monomer, carcinogenic compound, by sodium acrylate with good optical results at zero spatial frequency limit. Furthermore we have compared our PEA photopolymer (with and without crystal liquid molecules) with one commercial layer optimized for data storage applications. We have shown the potentiality of PEA to fabricate dynamic diffractive elements. Este trabajo está financiado por el "Ministerio de Ciencia e Innovación" (España) mediante los proyectos FIS2008-05856-C02-01 y FIS2008-05856-C02-02 y por la “Generalitat Valenciana” bajo el proyecto PROMETEO/2011/021.

Phase-only spatial light modulators (SLMs) are widely used in holographic display applications, including holographic image projection (HIP). Most phase computer generated hologram (CGH) calculation algorithms have an iterative structure with a high computational load, and also are prone to speckle noise, as a result of the random phase terms applied on the desired images to mitigate the encoding noise. In this paper, we present a non-iterative algorithm, where simple Discrete Fourier Transform (DFT) relations are exploited to compute phase CGHs that exactly control half of the desired image samples (those on even - or odd - indexed rows - or columns) via a single Fast Fourier Transform (FFT) and trivial arithmetic operations. The encoding noise appearing on the uncontrolled half of the image samples is reduced by the application of structured, non-random initial phase terms so that speckle noise is also kept low. High quality reconstructions are obtained under temporal averaging of several SLM frames. Interlaced video within half of the addressable image area is readily deliverable without frame rate division. Our algorithm provides about 6X and 20X reduction in computational cost compared to IFTA and FIDOC algorithms, respectively. Simulations and experiments verify that the algorithm constitutes a promising option for real-time computation of phase CGHs., European Research Council (ERC); European Union; Wear3D; Wearable Augmented Reality 3D Displays; FP7-IDEAS-ERC

We show an accurate procedure to obtain a Fourier transform (FT) with no dc term using a commercial twisted-nematic liquid-crystal display. We focus on the application to holographic storage of binary data pages, where a drastic decrease of the dc term in the FT is highly desirable. Two different codification schemes are considered: binary π radians phase modulation and hybrid ternary modulation. Any deviation in the values of the amplitude and phase shift generates the appearance of a strong dc term. Experimental results confirm that the calculated configurations provide a FT with no dc term, thus showing the effectiveness of the proposal. This work was supported by the “Ministerio de Educación y Ciencia (Spain)” under projects FIS2005-05881-C02-01 and FIS2005-05881-C02-02, and by the “Generalitat Valenciana” under Project GV06/007.

We report on near-field optical writing and topographic reading of spin-coated azo-polymethacrylate films with subwavelength resolution. The sample is functionalized with photosensitive side chain azobenzene groups. These photochromes are locally illuminated at 325 and 488 nm through the aperture of a metalized tapered optical fiber. The printing on subwavelength scale is due to optically induced cooperative rearranging of the polymeric chain. It is read in situ in the surface topography imaged by shear-force microscopy. The stability of the optically produced pattern and the cycling characteristics of the photoisomerization of the azobenzene molecules make these samples suitable for optical nanolithography and high density optical data storage.

Polarization modulated scanning near-field optical microscopy (PM-SNOM) is effective in detecting circular and linear dichroism with sub-wavelength resolution. PM-SNOM investigation of the chiroptical properties of single ribbon-like nanosized J-aggregates formed by acid induced aggregation of tris-(4-sulfonatophenyl)phenylporphyrin is reported. Linear dichroism maps give evidence of well-organized chromophores packed in linear arrays within the structure of the nanoribbons. Circular dichroism maps indicate that the molecules forming the nanoribbon have an inherently chiral structure at the local scale.

Under appropriate laser exposure, a thin film of InSb exhibits a sub-wavelength thermally modified area that can be used to focus light beyond the diffraction limit. This technique, called Super-Resolution Near-Field Structure, is a potential candidate for ultrahigh density optical data storage and many other high-resolution applications. We combined near field microscopy, confocal microscopy and time resolved pump-probe technique to directly measure the induced sub-diffraction limited spot in the near-field regime. The measured spot size was found to be dependent on the laser power and a decrease of 25% (100 nm) was observed. Experimental evidences that support a threshold-like simulation model to describe the effect are also provided. The experimental data are in excellent agreement with rigorous simulations obtained with a three dimensional Finite Element Method code.

Cataloged from PDF version of article. Abstract: Surface-enhanced Raman Scattering (SERS) of rhodamine 6G (R6G) adsorbed on biharmonic metallic grating structures was studied. Biharmonic metallic gratings include two different grating components, one acting as a coupler to excite surface plasmon polaritons (SPP), and the other forming a plasmonic band gap for the propagating SPPs. In the vicinity of the band edges, localized surface plasmons are formed. These localized plasmons strongly enhance the scattering efficiency of the Raman signal emitted on the metallic grating surfaces. It was shown that reproducible Raman scattering enhancement factors of over 105 can be achieved by fabricating biharmonic SERS templates using soft nano-imprint technique. We have shown that the SERS activities from these templates are tunable as a function of plasmonic resonance conditions. Similar enhancement factors were also measured for directional emission of photoluminescence. At the wavelengths of the plasmonic absorption peak, directional enhancement by a factor of 30 was deduced for photoluminescence measurements. ©2008 Optical Society of America

Tungsten oxide thin films have been deposited by pulsed dc magnetron sputtering of tungsten in argon and oxygen atmosphere. The as-deposited WO3 film is amorphous, highly transparent, and shows a layered structure along the edges. In addition, the optical properties of the as-deposited film show a steplike behavior of extinction coefficient. However, the electron beam irradiation (3.0 keV) of the as-deposited films results in crystallization, coloration (deep blue), and luminescence (intense red emission). The above changes in physical properties are attributed to the extraction of oxygen atoms from the sample and the structural modifications induced by electron bombardment. The present method of coloration and luminescence has a potential for fabricating high-density optical data storage device. � 2007 American Institute of Physics.

The finite-element method is applied to model phase-change recording in a grooved recording stack. A rigorous model for the scattering of a three-dimensional focused spot by a one-dimensional periodic grating is used to determine the absorbed light in a three-dimensional region inside the phase-change layer. The optical model is combined with a three-dimensional thermal model to compute the temperature distribution. Land and groove recording and polarization dependence are studied, and the model is applied to the Blu-ray Disc.

Magnetooptic (MO) effects in magnetic multilayers with periodically stratified regions are analyzed for the case of normal light wave incidence and polar magnetization (Faraday and polar Kerr effects). From the universal 4 x 4-matrix formalism simplified analytical representations restricted to terms linear in the off-diagonal permittivity tensor elements are obtained with no loss in accuracy. The MO effects are expressed as weighted sums of contributions from individual layers. Approximate expressions useful for the evaluation of trends in MO effects are given for periodic multilayers consisting of blocks with ultrathin magnetic films. The procedure is illustrated on periodic systems built of symmetric units. Limits on the ultrathin approximation are discussed.

Liquid-crystalline side chain polymers may open interesting application possibilities in the area of display and optical data storage if the response times of these materials can be made sufficiently fast. Thin, well aligned films of nematic homopolymers and copolymers, containing covalently bonded dyes, have been prepared and the optical switching times for the Freedericksz deformation depending on relevant polymer material and cell properties have been measured. It turns out that the switching times can be essentially shortened by raising the clearing temperature T sub IN. This is due to the exponential dependence of the rotational viscosity y sub 1 from the absolute temperature. We succeeded in lowering the switching time by nearly three orders of magnitude only by enhancement of T sub IN by 50 degree C, achieving the fast response of 2 ms with a nematic polymer.

Lippmann interference architectures are alternatives to holographic memories for high capacity data storage. In these systems, the image beam carrying the information data interferes with its reflection onto a mirror. The resulting interference pattern thus records a grating in the light sensitive material. Several images can be wavelength multiplexed at the same location. On the one side, and just as in holography, the number of images multiplexed in the same location is given by the wavelength Bragg selectivity of the thick gratings and is thus inversely proportional to the material thickness. On the other side, the page resolution is just diffraction limited and does not depend on this thickness. Each page can thus have a very large data content. Conversely to holography, no additional reference beam is required for recording. This absence of any reference beam simplifies the recording architecture at the expense on stringent requirements on the set-up adjustments. However, the potential numerous advantages of the Lippmann architectures seem to justify these constraints. One of these advantages is the possibility to easily implement an homodyne detection that greatly enhances the detected signals. Such homodyne detection of data pages is presented and discussed here for the first time.