Silicon planar-apertured probe array for high-density near-field optical storage

We propose a novel, to our knowledge, silicon planar-apertured probe array as an optical head for high-density near-field optical storage. In comparison with a conventional fiber probe employed for near-field optical storage the apertured probe array has a higher readout data-transmission rate and better mechanical durability. A probe array with an aperture size of 100 nm was fabricated by use of photolithography and wet etching of a silicon wafer. Subwavelength-readout capability was demonstrated by use of one aperture of the probe array. Furthermore, we achieved a 16 times increase in the light-transmission efficiency of the probe array by installing glass-sphere microlenses on each aperture. The increase was confirmed by measurement of the near-field optical intensity.     

Theoretical study of signal-to-noise ratio on near-field photochromic memory with fluorescence readout

The signal-to-noise ratio (SNR) on the fluorescence readout of a near-field photochromic memory was theoretically studied. Under various conditions the shot-noise-limited SNR was analyzed. SNR by bright spot recording (BSR) that was better than that by dark spot recording (DSR) was obtained under the condition of low writing power or wide bandwidth. Under the condition of bandwidth W = 1 MHz and P(write) = 10(-8) W only BSR can attain sufficiently high SNR, and the SNR was greater by as much as 30 dB than that of DSR. It was concluded that BSR is a promising method for high-density near-field photochromic memory with a fluorescence readout.     

Fluorescence readout of near-field photochromic memory

The fluorescence- and transmittance-detection readout methods of a near-field photochromic optical memory by a scanning-probe technique were studied theoretically. Shot noise, as the principal noise, was taken into account in an analysis of the signal-to-noise ratio (SNR). Under most conditions, fluorescence-detection readout yielded a better SNR than did transmittance-detection readout. For a transmittance change of 0.9-1.0 as a result of recording, a readout light power of approximately 100 nW, and a system bandwidth of 1 MHz, only the fluorescence-detection readout method, under the condition that the fluorescent layer of the medium have a fluorescence quantum yield greater than 0.4, can produce a sufficiently large SNR.     

Evanescent coupling in magneto-optical and phase-change disk systems based on the solid immersion lens

Results of numerical computations pertaining to evanescent wave coupling for near-field magneto-optical and phase-change disks based on the concept of the solid immersion lens are presented. We investigated the relation between the coupling efficiency and the width of the air gap in terms of the throughput of the recording process and the resolution of the readout signal. The simulations show a drastic decrease with a widening air gap of the coupling efficiency by means of evanescent waves into the recording medium. In magneto-optical readout, loss of the signal may be attributed to the reduction of magneto-optical interaction, the rise of reflectance, and the variation of the relative phase between the two components of polarization. In the phase-change readout the reduced reflectivity contrast between crystalline and amorphous marks is the cause of signal reduction.     

Superresolution Near-field Readout in Phase-Change Optical Disk Data Storage

Readout of a phase-change optical disk with a superresolution (SR) near-field structure (Super-RENS) is theoretically examined on the basis of three-dimensional, full-wave vector diffraction theory. Calculations have demonstrated that Super-RENS has a high spatial resolution beyond the diffraction limit in readout. The read signal is dependent on the nature of SR, the layer structure of the disk, and the state of polarization of the incident laser beam. For the Super-RENS in which antimony is used for SR readout, the readout signal is quite small, and the estimated carrier-to-noise ratio (CNR) is only ~30 dB for marks of 300 nm. For the Super-RENS in which a metallic region is formed during readout, the read signal is large, and the CNR can be as high as 50 dB in reading 300-nm marks.     

Optothermal property and decomposition characteristics of PtO(x) ultrathin film sandwiched between ZnS-SiO2 for super-resolution near-field recording

We have investigated the optothermal property and decomposition characteristics of PtO(x) ultrathin film protected by ZnS-SiO2 layers and effects of the constituent phases of PtO(x) on super-resolution capability and read stability of the super-RENS disk. All the ZnS-SiO2/PtO(x)/ZnS-SiO2 multilayers exhibited a steep reflectivity drop at the temperature range between 265 and 350 degrees C, corresponding to the decomposition of PtO(x). The decomposition temperature of the 4-nm-thick PtO(x) ultrathin film protected by ZnS-SiO2 layers was much lower than those obtained in thick PtO(x) films without protection. The activation energy for thermal decomposition was approximately 1.3 eV. Both the decomposition temperature and activation energy for thermal decomposition were unaffected by the constituent phases of PtO(x). Carrier to noise ratios (CNR) of over 40 dB for mark size of 150 nm were achieved in all super-resolution near-field structure (super-RENS) disks, while the super-resolution readout was limited to 2.5 x 10(3) approximately 4.5 x 10(4) cycles. The effect of constituent phases of PtO(x) on the super-resolution capability of super-RENS disk with a PtO(x) mask layer was minimal. However, as the constituent phases of PtO(x) mask layer transformed from a mixture of Pt and PtO, to pure PtO, and then to a mixture of PtO and PtO2, the readout stability of super-RENS disk increased dramatically since less heat was absorbed by the PtO(x) mask layer composed of PtO and PtO2 during the readout process, prohibiting the diffusion of materials inside the bubble to the GeSbTe phase change layer.     

Measurement of MKID Performance with High-Speed and Wide-Band Readout System

Microwave kinetic inductance detectors (MKIDs) are being developed at the National Astronomical Observatory of Japan to enable precise measurements of the cosmic microwave background. One of the features of MKIDs is scalability using a frequency-division multiplexing (FDMUX) readout scheme. A digital fast fourier transform spectrometer (FFTS) is a good way to read out a number of resonance frequencies simultaneously and fully utilize the advantage of FDMUX of MKIDs. We have developed FFTS readout electronics using an ADC/DAC with 1 Gsps (sample per second) sampling rate and 270 MHz bandwidth. We measured the noise characteristics of a single MKID in the frequency range of 60 Hz–30 kHz with this readout system, and found the noise was almost equivalent to the noise measured by ordinary analog IQ down-converter readout. This indicates our FFTS electronics do not add any additional noise to the MKID readout system over the frequency range.     

X-Ray Detection Using a Two-Transistor Active Pixel Sensor Array Coupled to an a-Se X-Ray Photoconductor

A direct-conversion X-ray sensor array using amorphous silicon (a-Si) thin-film transistor (TFT) based active pixel sensor (APS) readout circuit coupled with a stabilized amorphous selenium (a-Se) photoconductor for large-area digital imaging applications is presented. The pixel readout circuit employs a novel two-transistor (2T) active/passive pixel architecture that enables a compact pixel circuit for high-resolution sensor arrays with high large-area fabrication reliability. The X-ray detector consists of an in-house fabricated 150 $mu$m pixel pitch 2-TFT pixel coated with an 80 $mu$m thick a-Se photoconductor. A detector dark current of 110 pA/cm$^{2}$ at 10 V/$mu$ m electric field, and a controllable pixel conversion gain up to 8.4 nA/mR with a quantum efficiency of 60% was measured. Capabilities such as voltage programmable gain and dynamic range control, as well as nondestructive readout during X-ray exposure are demonstrated. The detector in this work represents a highly promising technology for high-resolution X-ray digital imaging, adaptable to a wide range of applications owing to its gain and dynamic range programmability.      

Reaction-mapped quantitative multiplexed polymerase chain reaction on a microfluidic device

We have applied multiple-time-point reaction mapping to generate high-dynamic-range quantitative data from PCR multiplexes. The approach measures, then compensates, numerous PCR slope nonidealities across the multiplex without prejudice. A multilane microelectophoresis device with a novel scanning detector that reports redundantly over more than six decades in signal strength was used to collect data with multiple readings for each amplification point and with double internal calibration (lane standards and gene standards). We investigated scaling properties and sensitivity for readout of 12plex PCR reactions. The sensitive detection, stemming from confocal optics, allowed reduction of the PCR cycle number by approximately five cycles compared to commercial fluorometric readout. This increased sensitivity appears to allow quantitative PCR over a dynamic range of >9 log2 abundance ratio in multiplex reactions exceeding 20plexes. We argue that the combination of mapping, multiplexing, and an internal standard, improves the per-well efficiency of quantitative expression analysis by a factor of 50-100 relative to fluorometric qPCR readout. Therefore, the approach is attractive for analysis of large gene networks at reduced cost.     

Recent Results of a New Microwave SQUID Multiplexer

We present recent results of a prototype microwave SQUID multiplexer containing four SQUIDs coupled to GHz frequency resonant circuits and fed with a single microwave readout line. The system is operating at a readout frequency range of 8–10 GHz. All four SQUIDs share a common DC bias and modulation lines. A new modulation scheme is tested to eliminate the need for individual flux biasing of the SQUIDs, which extends the dynamic range of the readout. In this scheme a common modulation signal is imposed on each SQUID and the received signal is demodulated at one and two times the modulation frequency to maintain sensitivity at any flux state. We also demonstrated a microwave RF bias scheme eliminating the necessity of the DC current bias to the SQUID. Our preliminary performance tests at 4.2 K show that the input noise of the device is ∼5 pA/ .      

Near-field optical recording with nanocomposite cover-layer for numerical aperture of 1.85

Near-field optical recording media with a nanocomposite cover-layer were prepared and tested using a gap servo, near-field recording system with an effective numerical aperture of 1.85. The refractive index of the nanocomposite cover-layer, which has a smooth surface, is 1.86, yielding a successful gap servo operation. However, the recording density cannot be maximized due to the refractive index of the cover-layer being lower than the required value for the effective numerical aperture. A recording density of 95?GB per disc can be achieved with a nanocomposite cover-layer having a refractive index of 1.86. The readout signal from 110?GB is not clear due to the reduced eventual numerical aperture in conjunction with the limited refractive index of the cover-layer.     

Nondestructive readout of a photorefractive hologram by phase-conjugate copying in a one-crystal configuration

We propose a novel phase-conjugate copying method for nondestructive readout of a volatile photorefractive hologram. In the one-crystal configuration, two holographic memories and a mutually pumped phase conjugator (MPPC) are formed within a single photorefractive crystal, instead of using multiple crystals. Two memories share the same hologram and complement each other in refreshing the hologram. A MPPC suppresses fanning noise and automatically aligns the wavefront of the reference and readout beams. We found the optimum configuration to achieve nondestructive readout from calculations and geometric consideration. In the experiments with a BaTiO(3) crystal, a continuous readout of 20 times longer than the recording time was achieved.     

Electrical Readout of Protein Microarrays on Regular Glass Slides

A new approach for the electrical readout of microarrays prepared on regular glass slides, using an array of impedimetric transducers (interdigitated electrodes, IDEs) is presented in this work. Impedance detection relies on the use of a urease-labeled immunoassay scheme. Urease is able to produce an increase in conductivity by hydrolysis of the urea substrate, which is measured with the IDEs and directly related to the amount of target analyte. Unlike previous electrical microarrays, the assay does not take place on top of the transducers but on a regular glass slide, which may enable the development of compact multiplexed analytical systems with lower cost per assay. A droplet of solution with the enzymatic substrate is deposited on each transducer of the array, and the microarray is positioned at a short distance (300 μm) so that each droplet wets one transducer and one spot of the microarray. This procedure allows reusing the transducer array for readout of a virtually unlimited number of microarrays. A microarray based on an immunoassay for the detection of a mouse generic protein in a concentration range from 0.03 to 30 μg mL(-1) was carried out to assess the performance of the electrical readout approach. A sigmoid response with a limit of detection of 0.1 μg mL(-1) and a dynamic range of 1 order of magnitude was obtained. A comparative study was also carried out with two well established analytical procedures. First, the urease-based immunoassay was tested in a 96 well microtiter plate using phenol red pH indicator and absorbance detection. Second, the microarray was carried out using the same target protein concentration range but applying a Cy3 label and fluorescence detection. Both assays allowed for the validation of the performance of the presented electrical readout system.     

In situ generation of surface plasmon polaritons using a near-infrared laser diode

We demonstrate a semiconductor laser-based approach which enables plasmonic active devices in the telecom wavelength range. We show that optimized laser structures based on tensile-strained InGaAlAs quantum wells-coupled to integrated metallic patternings-enable surface plasmon generation in an electrically driven compact device. Experimental evidence of surface plasmon generation is obtained with the slit-doublet experiment in the near-field, using near-field scanning optical microscopy measurements.     

反射式近场光学显微镜样品近场光分布特性

建立了一种反射式近场光学显微镜中样品近场光分布特性的模型,应用矢量衍射理论,得到了系统的场方程。在弱波动条件下,采用微扰法对场方程进行了求解,能方便地得到样品表面的各阶近场光反射和透射模复振幅表达式。计算结果表明,一级场分布要比零级场小一个量级,各阶近场信号的强弱完全由面形函数的傅里叶变换决定。通过与零级结果的比较,证明了计算结果的正确性。提供了一种计算样品表面近场分布简便方法,对反射式近场光学显微镜中调制检测技术具有指导意义。     

Study of a BGO calorimeter using electron and hadron beams from 1 to 50 GeV

A calorimeter of 25 bismuth germanate (BGO) crystals equipped with silicon photodiode readout has been tested at the CERN SPS in the energy range 1–50 GeV. The response for electrons has been shown to be linear in this energy range and the rms resolution obtained ( ) is approximately 1%, for E > 4 GeV. The electron/pion separation was found to be better than 1:500 in the energy range 1–20 GeV. Data on lateral and longitudinal shower development were compared with the results of a Monte Carlo simulation using the SLAC-EGS program and found to be in good agreement.     

On the reassessment of doses in TL-dosimetry by measuring the residual dose

Second readouts and the photo-transferred thermoluminscence (PTTL) method are sometimes used to reassess high doses. When using the common LiF:Mg,Ti, if the second readout is performed by a regular readout cycle of 13.3 s, its efficiency is low and the estimations cannot be obtained with acceptable accuracy for low doses in the 10-100 mSv range. By applying the PTTL method, the efficiency is much higher, but a high background is also present, deteriorating the quality of the reassessment. A simple and efficient method was studied, which consists of expanding the heating time to 30 s. Although the efficiency relative to a standard readout is improved by only a factor of 3, the low background enables to obtain results with the same uncertainty as the more complicated PTTL method. By applying region of integration discrimination, the errors can be further diminished.     

Beam test results of an ion-implanted capacitively coupled silicon strip detector processed on a 100 mm silicon wafer

A capacitively coupled silicon strip detector with 50 μm readout pitch has been tested in a pion beam at CERN. The spatial resolution of the detector equipped with LSI readout chips was 4.9 μm and the most probable signal-to-single-channel noise ratio was 31.     

The X-HPD—conceptual study of a large spherical hybrid photodetector

We present the results of a conceptual study demonstrating the feasibility of a large spherical hybrid photodetector with central anode. A prototype tube with 208 mm diameter and an anode in form of a metallic cube has been fabricated. In the final version of the so-called X-HPD concept the anode will be a scintillator cube with plated faces and a small photodetector to readout the bottom. The bialkali photocathode covers three quarters of the sphere surface. Combined use of this cathode in transmissive and reflective mode leads to effective quantum efficiency values exceeding those obtained in conventional hemispherical PMT designs. Further features of the concept are a photoelectron collection efficiency approaching 100% and a photon amplification in the scintillator crystal leading to a distinct single photoelectron signal.

Using a custom built electron accelerator based on a CsI transmissive photocathode, LSO and YAP block crystals in geometries adapted to the anode of an X-HPD have been tested with single photoelectrons in the 10–30 keV energy range. The scintillation light was readout with a conventional PMT or a Si-PM. More than 30 photoelectrons per incident electron could be detected with the PMT.     

The response of a compressible gas to extremely rapid transient, spatially resolved energy addition: an asymptotic formulation

An asymptotics-based analysis of the Navier–Stokes equations is used to study the response of an inert gas volume (the near-field) to localized, spatially distributed, transient energy deposition per unit mass, significantly larger than the ambient specific internal energy in the volume. The specified heat-addition time scale is chosen to be much less than the initial characteristic acoustic time of the affected volume. The evolutionary process in the near-field depends fundamentally on the ratio of energy deposition relative to the initial internal energy in the heated volume. A wide range of ratio values is found to be consistent with near-inertial confinement in the heated gas. The pressure rises directly with the very large temperature, the density is nearly constant and the internal Mach number of expansion is very small. The near-field response provides a piston-like source of compression waves in the surrounding cold environment (the far-field). When the energy ratio reaches an explicit, extreme value, inertial confinement fails, the gas dynamics are described by fully compressible flow equations, the temperature and pressure increases are extreme, density variations are modest and the internal and expansion Mach numbers are sonic. These near-field gas physics are shown to be compatible with the singular properties of far-field similarity solutions for strong blast waves, considered originally by von Neumann (The point source solution, NDRC, Div. B Report AM-9, 1941; revised in 1944; reprinted in von Neumann J (1963) In: Taub AH (ed) Collected works, vol VI. Pergamon Press, New York, pp. 219–237), Taylor (Proc Roy Soc Lond A 186:273–292, 1946), and Sedov (Prikl Mat Mekh 10:241–250, 1946). An asymptotic reformulation of the strong-blast-wave problem, using concepts similar to those in the near-field study, is used to rationalize and quantify ad hoc approximations by the aforementioned researchers.