High Recording Sensitivity Research Articles

Optical Electrophysiology: Toward the Goal of Label-Free Voltage Imaging.

Measuring and monitoring the electrical signals transmitted between neurons is key to understanding the communication between neurons that underlies human perception, information processing, and decision-making. While electrode-based electrophysiology has been the gold standard, optical electrophysiology has opened up a new area in the past decade. Voltage-dependent fluorescent reporters enable voltage imaging with high spatial resolution and flexibility to choose recording locations. However, they exhibit photobleaching as well as phototoxicity and may perturb the physiology of the cell. Label-free optical electrophysiology seeks to overcome these hurdles by detecting electrical activities optically, without the incorporation of exogenous fluorophores in cells. For example, electrochromic optical recording detects neuroelectrical signals via a voltage-dependent color change of extracellular materials, and interferometric optical recording monitors membrane deformations that accompany electrical activities. Label-free optical electrophysiology, however, is in an early stage, and often has limited sensitivity and temporal resolution. In this Perspective, we review the recent progress to overcome these hurdles. We hope this Perspective will inspire developments of label-free optical electrophysiology techniques with high recording sensitivity and temporal resolution in the near future.

First-principles study on the electronic structures and the absorption spectra of In: Mn: LiNbO3 crystals

The electronic structures and the absorption spectra of the indium and manganese codoped LiNbO3 crystals and their comparative groups are investigated by first-principles based on the density functional theory. The supercell crystal structures are established with 60 atoms, including four models:the near-stoichiometric pure LiNbO3 crystal (LN), the manganese doped LiNbO3 crystal (Mn:LN, charge compensation model as MnLi+-VLi+), the indium and manganese codoped LiNbO3 crystal (In:Mn:LN, charge compensation model as InLi2+-MnLi+-3VLi+), and the other indium and manganese codoped LiNbO3 crystal (In(E):Mn:LN, charge compensation model as InLi2+-InNb2--MnLi+-VLi+). The results show that the extrinsic defect levels within the forbidden band of Mn:LN crystal are mainly contributed by Mn 3d orbital electrons, which also affect the top of the valence band. The band gap of Mn:LN about 3.18 eV is narrower than that of LN; the band gaps of In:Mn:LN and In(E):Mn:LN sample are 2.82 and 2.93 eV respectively. The electron density of state (DOS) of manganese codoped LiNbO3 crystal shows that the orbits of Mn 3d, Nb 4d and O 2p superpose each other, i.e., forming covalent bonds, which result in conduction and valence bands shifting toward low energy. The indium ion does not contribute the extrinsic energy level within forbidden band, it affects the band gap through changing O2- electron cloud shape. The band gap narrows down if the indium ions occupy lithium ion positions, and becomes broad if the indium ions occupy niobium ion positions. It is found that the Mn:LN, In:Mn:LN and In(E):Mn:LN samples display the absorption peaks at 3.25, 3.11, 2.97, 2.85, 2.13 and 1.66 eV. The last absorption peak is contributed by the electron transferring from the Mn2+ energy level to conduction band, and the doping of indium ions leads to attenuation of this peak. The peak at 2.13 eV relates to the Mn3+, it is enhanced by the doped indium ions. The indium ions in crystal would influence the absorption, which relates to manganese ions, by transforming manganese ion valence via the formula as m Mn2++In3+→Mn3++In2+, that is, with the doping of the indium ions, the photorefractive center Mn2+ concentration decreases, which is responsible for the absorption peak at 1.66 eV. It must be mentioned that the Mn2+ possesses not only the shallow levels as mentioned previously, but also the deep ones which are responsible for the absorptions at 2.85 eV and other high energies. For the indium and manganese codoped LiNbO3 crystals, if the recording light is chosen at near 1.66 eV (748 nm), the relatively low concentration of indium ions is proposed to be chosen to achieve the high recording sensitivity.

OH− absorption and one-color holographic recording in Ru:Fe:LiNbO3 crystals varied co-doped with HfO2

A series of Ru:Fe:LiNbO3 crystals with various doping concentrations of HfO2 were grown by the Czochralski technique. Their defect structures were analyzed by the infrared absorption spectra and the Lorentzian fitting. The one-color holographic storage characteristics of these crystals were investigated by means of two-wavelength technology. The experimental results showed that fast response time of 12.7s and high one-color holographic recording sensitivity of 0.53cm/J were obtained in Hf(5mol%):Ru:Fe:LiNbO3 crystal, meanwhile the fixed diffraction efficiency was as high as 44.3%. These results indicated Hf, Ru and Fe co-doped LiNbO3 crystals were outstanding media for holographic storage applications.

Permanent data recording in transparent materials by using a nanojoule-class pulse laser

We investigated data recording for permanent data storage using an ultrafast pulse laser with nanojoule-class pulse energy and megahertz-class repetition rate in transparent materials, and driveless reading based on a simple imaging system. A transparent ceramics called Lumicera®, manufactured by Murata Mfg. Co., Ltd., was used as the recording medium. Lumicera® has a lower modification threshold and a higher recording sensitivity than those of silica glass, namely, the medium previously studied. Structural modification in Lumicera® occurs by light exposure for 10 μs, suggesting that Lumicera® has potential for a recording speed of over 100 kbps. Data recorded in Lumicera® resists heating for 2 h at 1000 °C and is expected to have a lifetime of over 300 million years. Moreover, the data recorded in Lumicera® was successfully read with a reading system based on a smart phone.

Comparison of two-color holography among different doped LiNbO3 crystals at low intensities

The effects of material and experimental parameters on the nonvolatile two-color holographic recording space charge field and sensitivity for different doped LiNbO3:Fe crystals have been studied theoretically based on a two-center model. When the direct electron transfer between the deep-trap centers and the shallow-trap centers was considered, the near-stoichiometric LiNbO3:Fe is confirmed theoretically to be of bigger space charge field and higher recording sensitivity than the LiNbO3:Fe:Mn and LiNbO3:Cu:Ce in the low intensity region. A further improvement of the recording sensitivity can be achieved by doping concentration, thermal reduction treatment of Fe, appropriate gating and recording wavelengths with large photo-excitation cross sections.

Improved nonvolatile holographic storage properties in Zr:Ru:Fe:LiNbO 3 crystal by blue light recording

Lithium niobate crystal triply doped with zirconium, ruthenium and iron was grown by conventional Czochralski method and its nonvolatile storage characteristics were investigated by means of two-wavelength technology, where blue and red beam were used as recording and readout light, respectively. In oxidized Zr:Ru:Fe:liNbO 3 crystal, short response time of 9.1 s and high recording sensitivity of 0.92 cm/J were demonstrated, together with high fixed diffraction efficiency of 44.9% maintained. These excellent properties were attributed to the elimination of intrinsic defects by ZrO 2 doping and effective excitation of electrons by blue light. Our experimental results indicated this doped LiNbO 3 crystal was an outstanding medium for holographic storage applications.

High-Speed Flexible Optical Disk for Broadcast Archival Storage

We developed a prototype of a flexible optical disk (FOD) drive with a mechanical stabilizer. We prepared the FOD that had a high recording sensitivity of a recording layer and had low byte error rates below 2 ×10-4 at speeds from 36 to 252 Mbps, and examined the recording of video data on the FOD and the drive. We could record and play a high-definition television (HDTV) video (MPEG-2, 422P@HL) seamlessly at 144 Mbps over the entire area of the FOD and the FOD drive with broadcast video systems. We confirmed that the FOD and the FOD drive can record and play HDTV signals for professional broadcast use.

A 252-Mb/s Recording Experiment Using Flexible Optical Disks for Broadcast Use

Flexible optical disks (FOD) have a feasibility of their high data-transfer rate and large capacity for archival storage. We have been developing the FOD in order to replace as the media with a current professional video cassette recorder (VCR) of HD-D5 format which have a data-transfer rate of more than 250 Mb/s. Here, we developed the FOD with the high recording sensitivity for high-speed recording, and succeeded to record the 252 Mb/s data with the high-speed tracking control method and optimized write strategy. We also employed the partial response maximum likelihood (PRML) read channel for playback data. We could get and achieve the low byte-error rate (BER) below 2 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> at the recording speed of 252 Mb/s, enough to record the video signals of HD-D5 VTR for professional broadcast use.

Properties of New Fluorinated Holographic Recording Material for Collinear Holography

A new fluorinated holographic recording material is applied with a view to realizing holographic information system (HIS) media that offer high multiplexing numbers and high recording sensitivity. We report here, for the first time, the successful recording and reconstruction of 750 multiplexed holograms on a 50 ×50 mm2 photopolymer coupon sample based on a novel fluorinated holographic recording material for collinear holography. The proposed material yields bit error rates (BERs) less than 10-2 in the X–Y plane of the coupon sample and thus is suitable for 532 nm optical data storage. It's fundamental properties, such as the relationship between BER and number of holograms, are determined. This new fluorinated material offers improved error maps as evidenced by the 0.4-mm-thick, 120-mm-diameter photopolymer disc. The average error rate is 1.61% for the disc sample. This new material successfully stored and reproduced a short segment of animated video data.

Crystallization and Melting Kinetics of Zn-Doped Fast-Growth Sb70Te30 Phase-Change Recording Films

Doping Zn into the fast-growth Sb70Te30 recording film can improve the archival stability and recording sensitivity, but the initialization and erasing processes will become more difficult. In order to obtain sufficiently high recording sensitivity and archival stability, while maintain adequate initialization and erasing abilities for the rewritable optical memories, the optimal doping concentration of Zn in the Sb70Te30 recording film should locate between 5.3 and 17.9 at. %.

A new class of holographic recording constructed by hyperbranched polymers dispersed in photopolymer film

We demonstrate a new class of holographic recording constructed by hyperbranched polystyrene (HPS) or poly(ethyl methacrylate) (HPEM) dispersed in methacrylate photopolymers. Hyperbranched polymers behave as hard spheres in monomer and diffuse easily into gel networks without any aggregation. Holographic gratings are constructed by anisotropic distributions of polymer and hyperbranched nanoparticle layers formed by photo-polymerization of methacrylate monomers following phase separation of hyperbranched nanoparticles in the form of interference patterns by irradiation of two laser beams of different phase. High-contrast refractive index changes (Δn) with high recording sensitivity and dimensional stability are achieved for the system of HPEM-[2-methylacrylic acid 2-4-[2-(2-methylacryloyloxy)-ethylsulfanylmethyl]-benzylsulfanyl ethyl ester] (UV3000) as methacrylate monomer.

The role of FA:K+ and FA:Na+ defects in laser light generation and color image formation at the (100) and (110) surface sites of AgCl and AgBr.

FA:K+ and FA:Na+ color centers at the low coordination (100) and (110) surface sites of AgCl and AgBr thin films play important roles in providing tunable laser oscillation and color image sensitization. Double-well potentials at these sites are investigated using ab initio molecular electronic structure calculations. Quantum clusters were embedded in simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces, and ions that are the nearest neighbors to the FA defect site were allowed to relax to equilibrium. The calculated Stokes shifted optical transition bands suggest that laser light generation is sensitive to (i) the lattice anion, (ii) the coordination number of surface ions, (iii) the dopant cation, (iv) the vibrational coupling mode, and (v) the choice of the basis set centered on the anion vacancy. An attempt has been made to explain these results in terms of Madelung potentials, electron affinities and optical–optical conversion efficiencies. All relaxed excited states of the defect-containing surfaces were deep below the lower edges of the conduction bands of the ground state defect-free surfaces, suggesting that FA:K+ and FA:Na+ are suitable laser defects. The probability of orientational destruction of the two centers, attributed to the assumed saddle point ion configurations along the 〈110〉 axis, was found to be dependent on the lattice anion, the coordination number of surface ions, and the dopant cation. For optical memories, a high recording sensitivity was assigned to FA:Na+ relative to FA:K+, to the (110) surface relative to the (100) surface, and to AgCl relative to AgBr. The dependence of exciton (energy) transfer on the lattice anion, the coordination number of surface ions, and the dopant cation was clarified. The Glasner–Tompkins empirical rule was generalized to include the surface coordination number and the dopant cation in addition to the lattice anion. As far as color image formation is concerned, the examined supersensitizer was found to increase the sensitizing capabilities of two primary dyes in the excited states by increasing the relative yield of quantum efficiency. The (110) surfaces of AgBr and AgCl were more sensitive than the corresponding (100) surfaces, and the AgBr thin film was found to be more sensitive than that of AgCl. Based on quasi Fermi levels, the difference in the sensitizing capabilities between the examined dyes in the excited states was determined.

The role of FA(I):Tl+ and FA(II):Ga+ defects in laser light generation and photographic sensitization at the low-coordination surface sites of AgBr first principles calculations

Abstract FA(I):Tl+ and FA(II):Ga+ color centers at low coordination surface sites of AgBr thin films play important roles in providing tunable laser oscillation and photographic sensitization. Double-well potentials at these sites are investigated using ab initio molecular electronic structure calculations. Clusters of variable sizes were embedded in simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces, and ions that are the nearest neighbors to the FA defect site were allowed to relax to equilibrium in each case. The calculated Stokes shifted optical transition bands suggest that laser generation is too sensitive to the simultaneous effects of (i) the dopant cations size (ii) the coordination number of the surface ions, and (iii) the choice of the basis set centered on the Br vacancy. An attempt has been made to explain these results in terms of Madelung potentials, electron affinities and optical–optical conversion efficiencies. All relaxed excited states of the defect containing surfaces were deep below the lower edges of the conduction bands of the ground-state defect-free surfaces, indicating that FA(I):Tl+ and FA(II):Ga+ are suitable laser defects. The probability of orientational destruction of the two centers, attributed to the assumed saddle point ion configurations along the 〈1 1 0〉 axis, was found to be directly proportional to the size of the dopant cation, and inversely proportional to the surface coordination number. For optical memories, a high recording sensitivity was assigned to FA(II):Ga+ relative to FA(I):Tl+ and to the flat surface relative to the edge and corner surfaces. The possibility of exciton (energy) transfer between sites of different coordination numbers was clarified. The relaxation and defect formation energies were calculated. The Glasner–Tompkins empirical relation was generalized to include the dopant cations and surface coordination. As far as photographic sensitization is concerned, the highest occupied molecular orbital of only one out of three acyclic developers was found to be high enough for electron transfer to the Fermi level of the silver bromide thin film. The FA defect formation and rotational diffusion of the central silver cluster broaden the energy gaps between the highest occupied molecular orbitals of the developer molecules and the lowest unoccupied molecular orbitals of the defect containing surfaces and make the process of electron injection less facile. About 59% of the reduction of silver ions at the flat surface of silver bromide is attributed to the host anions and FA defect formation, leaving about 41% for the reduction of photoelectrons and developer molecules. The unrelaxed rotational diffusions of the central silver clusters by 30° decrease the latter percentage to about 10%, but are severely hindered by activation energy barriers.

Holographic recording in TiO2 nanoparticle-dispersed methacrylate photopolymer films

We demonstrate permanent holographic storage in the green with high diffraction efficiency and recording sensitivity in TiO2 nanoparticle-dispersed methacrylate photopolymer films. It is shown that the diffraction efficiency as well as the recording sensitivity significantly increase with an increase of nanoparticle concentration. It is also found that volumetric shrinkage during holographic exposure is noticeably suppressed by inclusion of the nanoparticles.

Bleaching effect and nonvolatile holographic storage in doubly doped LiNbO3:Fe:Cu crystals

The bleaching effect, i.e. the crystal shows that decoloration after it is illuminated by ultraviolet light, has been observed in congruent LiNbO3:Fe:Cu crystals. Based on this bleaching effect, a new technique including the recording phase by two interfering red beams and fixing phase by both UV light and a coherent red beam has been experimentally investigated to realize nonvolatile holographic storage in LiNbO3:Fe:Cu. The results of proof-of-concept experiments confirm that bleaching effect becomes an alternative physical mechanism for nonvolatile holographic stor age with high recording sensitivity and weak light-induced scattering noise.

外部磁界耐性を有する単磁極ヘッド

A new head design for a single-pole head is proposed. The head is driven with pancake-structure dual coils, which sandwich a main pole and excite a main-pole tip effectively. High recording sensitivity was achieved in comparison with a conventional single-pole head. Furthermore, since the main pole is sandwiched between two return-path yokes, which act as a magnetic shields, a high robustness with regard to external stray fields was confirmed, up to at least an external field of 20 Oe.

High writing-sensitivity single-pole head with cusp-field coils

A new design for a high writing-sensitivity single-pole head is proposed. The head is driven with regular pancake structure dual coils, which sandwiches the main-pole. The outer parts of both coils are exposed to the air bearing surface. These coils can generate a cusp field with bifilar connection. A high recording sensitivity of this new head has been clarified by the fact that a small magnetomotive force of less than 0.1 AT/sub 0-P/ can saturate a medium with a high-coercivity of 3.5 kOe.

Rewritable Dual-Layer Phase-Change Optical Disk

This paper describes the development of a rewritable phase-change optical disk with a dual-layer structure. To obtain equivalent signal amplitude and recording sensitivity from the medium located on the beam incident side (the first medium) and the medium beneath (the second medium), we developed a high transmittance first medium featuring a very thin recording film (7 nm) and no reflection layer, and a high recording sensitivity and high reflectivity second medium with a semi-transparent front layer and a reflection layer. We confirmed a jitter of approximately 10% for both media at a recording density corresponding to 8.5 GB on a 120 mm disk. The laser power required to record on the first medium was 12 mW, and the second medium, 13 mW. It was also confirmed that the new rewritable dual-layer phase-change optical disk possesses the potential for operation with a blue laser.

Fabrication and Recording Characteristics of a Single-Pole Flying Head

We fabricated a novel single-pole head on a flying slider for perpendicular magnetic recording. By using three film-conductors to energize a main pole at its end, a high recording sensitivity of 0.03 ATP-P and a very low inductance around 10 nH were obtained. A D50 value of 135 kFRPI was confirmed, almost the same at that of a bulk coil songle-pole head in sliding contact recording. This head provides an idea of a practical single-pole head for a double-layered perpendicular medium for high-frequency applications.

High density recording with a visible laser diode in direct overwrite MO disk

To achieve a higher storage density on an overwritable exchange-coupled quadrilayer magnetooptic (MO) disk, the overwrite recording characteristics using the optical head with 680-nm laser diode were investigated. High recording sensitivity was obtained and the write power was estimated to be about 10 mW at 22-m/s linear velocity. Carrier-to-noise ratio (CNR) of more than 46 dB was obtained at the 0.66- mu m mark length, and 0.5- mu m/b recording with a bit error rate less than 1*10/sup -5/ was obtained at 1.2- mu m track pitch. The authors conclude that 130-mm double-sided direct overwrite MO disk could have 2.5 Gbyte storage capacity. If 1.0- mu m track pitch disk can be used, a storage capacity of 3.5 Gbyte might be expected. >