Optical Information Storage Research Articles

Time-Dependent Density Functional Theory Studies of the Photoswitching of the Two-Photon Absorption Spectra in Stilbene, Metacyclophenadiene, and Diarylethene Chromophores

Photochromophores such as cis-stilbene (1a), metacyclophenadiene (2a), and the diarylethene 3a undergo photoinduced conrotatory opening and closing of a central bond and are currently being sought out as potential candidates for media within 3D optical information storage devices. Strong molecular two-photon absorption (inducing the reversible photoisomerization) is a necessary feature for this application due to the need for high 3D spatial resolution. Here, the one- and two-photon absorption (OPA and TPA) characteristics of the open- and closed-ring isomers of 1-3 have been investigated using time-dependent density functional theory. It was determined that the excited states populated by two-photon absorption were nearly 1 eV higher in energy than the lowest energy excited state populated by one-photon absorption. The electronic structures of the TPA and OPA accessed states were then compared utilizing natural transition orbital analysis. There, it was found that states excited by OPA had pipi* character about the C-C framework associated with the bond formation/scission of the central C-C bond. In contrast, the states populated by TPA have pipi* character along the C-C skeletal periphery, including phenyl excitations. It is postulated that these differences in excited state electronic structure may lead to reaction pathways alternative to photoisomerization about the central C-C bond, impacting the utility of these compounds as 3D information storage media.

On the Time Dependent Features of the Two-Colour Light Pulses Propagation in the Sodium Vapour

The development of the electromagnetically induced transparency (EIT) technique, reviewed by Harris [1], resulted in the slowing down of the light [2–4] and the storage of optical information [5–7]. Both these effects, slow light and light storage, showed a good relation to the quantum interference effect [8 and references therein]. The group velocity reduction has been considered in different connections. A method based on the steady state solution showed the mechanism for the loss of the probe field [9]. The slow light propagation in an open three level system has been analyzed numerically in [10]. Kasapi et al. [11] have described the group velocity reduction associated with the propagation dynamics for EIT pulses in Pb vapour. Furthermore, Greentree et al. [12] have demonstrated the influence of turn-on and turn-off transients on the EIT in Rb magneto-optical trap. Roberts et al. [13] have calculated the ground state collisional decay rate that limits delay and storage times in EIT experiments with condensates. The nonlinear process associated with the group velocity reduction, such as pulse compression, has been demonstrated by Harris and Hau [14]. The soliton behaviour in three-level system has been discussed in [15, 16 and reference therein]. It has been

Optical storage of high-density information beyond the diffraction limit: A quantum study

We propose an optical readout scheme allowing a proof of principle of information extraction below the diffraction limit. This technique, which could lead to improvement in data readout density onto optical disks, is independent from the wavelength and numerical aperture of the reading apparatus, and involves a multipixel array detector. Furthermore, we show how to use nonclassical light in order to perform a bit discrimination beyond the quantum noise limit.

High‐Density Data Recording in an Optoelectrical Dual‐Responsive Thin Film

High-density data storage has been receiving much attention with the ever-increasing amount of stored data and the continuous miniaturization of optoelectronic devices. To increase the storage density, various recording schemes have been explored; these include scanning tunneling microscopy (STM) for achieving maximal area density and two-photon excitation (TPE) for recording information in multiple layers ; these techniques are considered as two of the most attractive. Meanwhile, the development of novel recording media is also a critical factor to achieve high-density storage. Organic materials, due to their good stimuli-responsive properties, versatility in molecular design, and low cost, have been proved to be promising candidates. In past decades, great progress has been made using different organic media both in nanoscale electrical data recording and in high-density optical information storage, which utilize their electrical bistability and light characteristics such as refractive index, fluorescence properties, and absorption spectrum. However, most of these achievements were based on the single-mode (photon or charge) modulation of the recording materials. For practical application in high-density data storage and also to enhance the multifunctionality of optoelectronic devices, media that would permit the manipulation of optical and electrical signals with alternative operating modes such as multimode are more desirable. Although it has been proposed that multiple physical channels, such as optical, electrical, and magnetic schemes, could be utilized for recording and transmitting information using a multifunctional material, so far there have been few reports on simultaneously achieving optical and electrical recordings in a stable material. The main problems may be the difficulty in finding a suitable multiresponse medium, and amplifying the effects of molecular multiresponse in the solid state.

Storage and Erasure of Optical Information in Pt-PZT-SnO2 Thin Film Structures

We have studied the effect of optical radiation on the conductivity of a thin film field effect transistor based on a Si-SiO 2 -Pt-PZT-SnO 2− x -Pt multilayer structure. Within an admissible radiation dose, the conducting channel possesses a persistent photoconductivity, with an optical data storage time of at least 10 5 s. Effective channel impedance control by an electric field applied to the thin-film ferroelectric-semiconductor structures is demonstrated. The persistent photoconductivity in the studied multilayer structure may be quenched by only an increase of temperature, for example, using heating by an alternating switching electrical field.

Erbium photoluminescence in opal matrix and porous anodic alumina nanocomposites

“Self-organizing” design methods of nanocomposites based on cubic packing SiO 2 nanospheres (opal matrices) and porous anodic alumina (PAA) are considered. The photoluminescence of nanocomposites doped with erbium and other rare earth elements is studied versus the element structure, concentration of rare earth ions, matrix composition, optical properties, and technology. Possible application of 3D-(space) and 2D-(planar) nanocomposites in systems of optical information transfer, storage, and processing are discussed.

Grating Decay in Reduced Barium Titanate Crystals

Under inhomogeneous illumination, a refractive index grating will form in a barium titanate crystal through the photorefractive effect. Due to its large electro-optic coefficients and self-pumped phase conjugation, a photorefractive barium titanate crystal is of a special interest for many applications such as optical signal processing, optical phase conjugation and optical information storage. In general, the grating stored in a barium titanate crystal will fade in the dark soon. That is a barrier for the applications of optical information storage. Here we made a series of reduced BaTiO3 crystals and investigated the optical absorption, the dark decay and the light-induced decay. We found that the decay time of the grating can be lengthened by the reduction treatment. The grating can be kept in the crystal reduced around compensation point for more than a month. At high intensity, the speed of writing/erasing a grating can be determined by the optical absorption.

Novel Polymer Nanocomposites with Giant Dynamical Optical Nonlinearity

The giant optical nonlinearity of a novel organic nanocomposite based on a conducting polymer, namely, poly(9-vinylcarbazole), and quinone derivatives as a charge photogenerator is investigated. The change in the refractive index of a thin polymer film (60 μm thick) is determined to be Δn = −7.3 × 10−3. The inference is made that the origin of the optical nonlinearity is associated with the difference between the polarizabilities of the quinone molecule and the quinone radical anion formed under exposure to laser radiation. The optical nonlinearity is examined using two methods: (i) the self-action of a Gaussian beam in a layer of the material and (ii) Z-scan measurements of a thin film at a wavelength of 633 nm. These nanocomposite materials can serve as active media in diverse applications, including image processing, high-density optical information storage, and phase conjugation.

Exploitation of Localized Surface Plasmon Resonance

AbstractRecent advances in the exploitation of localized surface plasmons (charge density oscillations confined to metallic nanoparticles and nanostructures) in nanoscale optics and photonics, as well as in the construction of sensors and biosensors, are reviewed here. In particular, subsequent to brief surveys of the most‐commonly used methods of preparation and arraying of materials with localized surface plasmon resonance (LSPR), and of the optical manifestations of LSPR, attention will be focused on the exploitation of metallic nanostructures as waveguides; as optical transmission, information storage, and nanophotonic devices; as switches; as resonant light scatterers (employed in the different near‐field scanning optical microscopies); and finally as sensors and biosensors.

A quantitative measurement for the photorefractive index modulation of reflection gratings in LiNbO 3

Photorefractive crystals, in particular LiNbO 3, can be used for the storage of optical information. The storage capacity is related to the photorefractive index modulation of grating, Δ n. This article is the first to report the use of wavelength detuning to measure the Δ n for the reflection type of grating. The method involves extracting the half-width Δ λ 1/2 from the wavelength scan of the diffraction efficiency for a reflection grating and using an experimental correlation between Δ λ 1/2 and Δ n derived in this article to calculate the photorefractive index modulation, Δ n. The half-width Δ λ 1/2 of 0.14 Å is the narrowest selectivity reported thus far (attained by using a narrow band laser source), and allows us to deduce the Δ n of this reflection grating as 3.7 × 10 −5 using the above correlation.

LAYERED MATERIAL HOLDS MORE DATA

CLEVER GEOMETRY IS THE basis of a new material that is said to be ideal for secure data encryption and dense optical information storage { Adv. Mater. , 16 , 516 (2004)}. material consists of a lattice of onionlike spheres in which the particle core and its layers each contain a different dye. material can hold four or more pieces of information in one spot—not just two as in binary optical data storage. And it opens a door to high-density three-dimensional optical data storage. The approach is really simple, says lead researcher Eugenia Kumacheva, associate professor of chemistry at the University of Toronto, who worked with postdocs Ilya Gourevich and Hung H. Pham and microscopist James E. N. Jonkman. They start with colored colloids—polymeric nanospheres labeled with a dye—for example, an ultraviolet dye. Then they envelop the nanosphere, what Kumacheva calls the core, with a shell of another polymer labeled ...

New polyamides with azo-chromophore groups

A series of four novel polyamides with semiflexible main chains were prepared from two azo-chromophore diamines: 2,4-diamino-4′-nitroazobenzene and 2,4-diamino-4-azo-(4′-nitroazobenzene)benzene. Polymers were obtained from diacid chlorides by the polycondensation reaction in DMA solution. The polymers were identified by infrared, 1H NMR spectroscopy and elemental analysis. The thermal properties of these polymers were investigated using differential scanning calorimetry (DSC) method and thermogravimetric analysis. The presence of photoisomerisable azobenzene groups makes them interesting for the optical information storage and processing. We have checked that thin films casted on glass plates from these polymers are suitable substrates for holographic polarization grating recording realized by laser light of 514.5-nm wavelength. The kinetics of grating recording observed within the studied group of polymers is discussed in relation to structural properties of the polymers. Such type of materials could find potential applications in photonics.

UV-laser-light-produced defects and reversible blue–white photoluminescence change in silica

The photoluminescence (PL) color of silica glass changes from weak blue to intense white under irradiation with 325nm laser light at room temperature in vacuum. Irradiation at room temperature with the same laser light under oxygen gas atmosphere erases the white PL state. Through many successive experiments, it is found that the spectral change is a reversible phenomenon. Such intense white PL state is stored for a long time at room temperature in air under room light after removal of the laser light, in spite of any changes of atmosphere. The observed phenomenon may relate to the photo-induced defect formation at the silica glass surface. Such observed reversible phenomenon may well yield materials for erasable optical information storage, oxygen sensors and white-light emitting devices.

Syntheses and properties of polyurethanes containing side‐chain azobenzene groups

AbstractPolymers containing azobenzene groups have the characteristic reaction of photo‐induced cis–trans isomerism. The study of new materials for optical information storage has prompted making use of these photo‐isomerizations. In this study, we report the syntheses and properties of four different polyurethanes (DR‐PUns) containing azobenzene groups in the side‐chains. The structurally similar polyurethanes (DR‐PUns) were synthesized by the polycondensation reaction of Disperse Red 19 (DR 19) and four different diisocyanates in dimethylformamide. By introducing of DR 19 into the polymer, we obtained polymers containing a photochromic group in the side‐chain. The weight‐average molecular weights of the DR‐PUns were in the range 5500–12 900. The Tgs of the DR‐PUns range from 119.5 °C to 157.0 °C, depending on the structure of the diisocyanate. Optical properties and solubilities of the polyurethanes were compared. The diffraction efficiencies of films were measured as a function of the reaction time. Typically, the diffraction efficiencies of the DR‐PU1 film prepared from toluene 2,4‐diisocyanate were observed up to a level of 0.25%. For the DR‐PU1 film, the effect of the intensity of the induced laser beam on the diffraction efficiency is also discussed.© 2003 Society of Chemical Industry

Photoswitchable molecular receptors

The review describes photoswitchable molecular receptors based on crown-ether systems. The important feature of the systems is reversible change in the capacity of a photochromic host molecule for association with guests upon irradiation. From the other side, the exploration of the complex formation process in crown-ether systems leads to a novel approach to the modification of photochromic behavior. The results obtained show that the introduction of crown-ether moieties into dye molecules affords compounds that can change their spectral and photochromic properties upon complex formation. The researchers believe that the novel photochromic systems can now be regarded as being promising for traditional applications (photochromic ophthalmic lenses or camera filters, reversible holographic systems and cosmetics) and molecular electronics, biomimetic chemistry, and optical information storage.

Improvement of the diffraction properties in holographic polymer dispersed liquid crystal bragg gratings

Holographic polymer dispersed liquid crystal (HPDLC) is a new kind of holographic material. It can be fabricated by the photo-initiated polymerization-induced phase separation. HPDLC Bragg grating is composed of parallel, periodic polymer-rich and liquid crystal-rich lamellae. The diffraction efficiency (DE) can be switched by the application of electric field. HPDLC devices are potentially useful for optical communication, information storage and display. How to increase the diffraction efficiency is the key to application. We investigated the dependence of DE on different monomers, liquid crystal content, exposure intensity and time, and exposure temperature. The best conditions were founded to make the diffraction properties improved. Now the highest DE was 80.2%. The HPDLC grating morphologies were also observed and analyzed by scanning electron microscope (SEM).

Optimization of diffraction properties for holographic polymer dispersed liquid crystal

Holographic polymer-dispersed liquid crystal (HPDLC) is a kind of switchable volume holography. It can be manufactured according to the photo-initiated polymerization-induced phase separation. HPDLC is composed of parallel, periodic polymer-rich and liquid crystal-rich planes. The diffraction efficiency can be modulated by the application of electric field. HPDLC devices are potentially useful for optical communication, information storage and display. How to increase the diffraction efficiency is the key to application. We investigated the dependence of diffraction efficiency on the refractive index of the polymer, exposure intensity, liquid crystal loading and temperature. The best conditions were found to make the diffraction properties optimized. Now the highest diffraction efficiency was 802%. The HPDLC morphologies were also observed and analyzed by scanning electron microscope (SEM).

Photoresponsive self-assembled monolayer∕photopolymer film for optical information storage using liquid crystals

Ultrathin films of alkoxy alkyl amino silanes functionalised with photochromophore moieties have been grown on glass and quartz substrates by self-assembly (SA) techniques. The films have been selectively photodimerised with polarised UV light using photomasking to produce anistropic ordered structures locally. These ordered structures produce uniform planar orientation of nematic liquid crystals. Liquid crystals being birefringent (Δn=≈0.10–0.25), a high optical contrast is produced between uniformly aligned and non-aligned regions when viewed between crossed polarisers. This has given rise to the possibility of creating a new type of optical storage liquid crystal display. It has been possible to store line patterns with a line resolution of ≈20 μm by this technique. Such films can be used to record holographic gratings using UV polarised light.

Photostimulated luminescence from CaS:Eu,Sm clusters embedded in organic dye

The optical properties of rare-earth ions in an organic dye matrix have been studied because of their possible application for optical information storage. Strong IR photostimulated luminescence of CaS:Eu,Sm doped organic dye films was revealed in the sample prepared by the sol–gel method. It was found that the efficiencies of photostimulated luminescence in the CaS:Eu,Sm doped pyrazoline dye films are higher than that in the inorganic CaS:Eu,Sm materials. The grain size of the nanocrystallites, determined by X-ray diffraction, is approximately 50 nm. It was shown that the absorption spectra for organic dye films exhibit a remarkable anisotropy near a wavelength of 310 nm.

Nanophotonics: a new multidisciplinary frontier

Nanophotonics, defined as nanoscale optical science and technology, is a new multidisciplinary frontier. This article presents our studies on nanoscale matter–radiation interactions utilizing nanoscale confinement of radiation as well as on nanoscale photochemical transformations, particularly nanoscale nonlinear optical interactions. The selected examples of our studies include nanoscopic optical harmonic generation, multiphoton fluorescence, transient absorption dynamics, surface-plasmon-enhanced two-photon fluorescence, and nonlinear optical information storage.