Graphene valley filter using a line defect

With its two degenerate valleys at the Fermi level, the band structure of graphene provides the opportunity to develop unconventional electronic applications. Herein, we show that electron and hole quasiparticles in graphene can be filtered according to which valley they occupy without the need to introduce confinement. The proposed valley filter is based on scattering off a recently observed line defect in graphene. Quantum transport calculations show that the line defect is semitransparent and that quasiparticles arriving at the line defect with a high angle of incidence are transmitted with a valley polarization near 100%.     

Generation of hollow beams by using a binary spatial light modulator

We demonstrate the generation of hollow laser beams by using a binary spatial light modulator and compare the results with those for a continuous modulator. The binary phase modulator produces beams that have continuous, azimuthally varying phase profiles and can be dynamically changed with kilohertz refresh rates. The intensity and phase profiles are recorded through the focus of an imaging lens and are compared with scalar diffraction theory. We highlight properties of the beams relevant to optical dipole traps.     

Generation and characterization of a bright X-ray source using picosecond laser

High-resolution soft X-ray spectra of H-like and He-like ions were produced from laser irradiated silicon and aluminum targets. Plasma size was about 100 μm. X-ray spectra were analyzed to determine plasma parameters. We compared the line shape of resonance transitions and their intensity ratios to corresponding dielectronic satellites and the intensities of the inter combination lines of He-like ions, with the results of model calculations. Such comparison gave average values of the electron density N _e=(1?1.9)×10²¹ cm^?3 and the electron temperature T _e=460–560 eV for Si plasmas and about 560 eV for Al plasmas produced by the first and the second laser harmonics. According to our estimations, more than 10¹² photons were produced within the resonance line spectral width and in the solid angle 2π steredian during the total decay period.     

Reflection of an acoustic line source by an impedance surface with uniform flow

An exact analytic solution is derived for the 2D acoustic pressure field generated by a time-harmonic line mass source located above an impedance surface with uniform grazing flow. Closed-form asymptotic solutions in the far field are also provided. The analysis is valid for both locally-reacting and nonlocally-reacting impedances, as is demonstrated by analyzing a nonlocally reacting effective impedance representing the presence of a thin boundary layer over the surface. The analytic solution may be written in a form suggesting a generalization of the method of images to account for the impedance surface. The line source is found to excite surface waves on the impedance surface, some of which may be leaky waves which contradict the assumption of decay away from the surface predicted in previous analyses of surface waves with flow. The surface waves may be treated either (correctly) as unstable waves or (artificially) as stable waves, enabling comparison with previous numerical or mathematical studies which make either of these assumptions.     

Air filter sterilization using a one atmosphere uniform glowdischarge plasma (the volfilter)

Two characteristics of microorganisms-extremely small size (0.01 to a few micrometers) and the ability to reproduce-hinder the effective filtration of bacteria and viruses from indoor air. The microorganisms captured by a filter in spite of their small size can reproduce in situ and be released into the airstream, giving rise to the “sick building syndrome”. The application of the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP) to a filter can address both these issues. At University of Tennessee at Knoxville, we have recently developed the “Volfilter”, a planar version of the OAUGDP produced by attaching strip electrodes to both sides of a sheet of dielectric filter material and energizing the electrodes with a high-voltage, low-frequency RF source. After the filter material removes microorganisms from the airstream, the OAUGD plasma kills the captured microorganisms. The combination of an appropriate filter material and periodic application of the OAUGDP results in an effective capture and sterilization device even for the smallest microorganisms and requires minimum maintenance. This paper will describe results obtained during the operation of a laboratory-scale “Volfilter” challenged by two kinds of microorganisms, S. aureus and the bacterial virus Phi X 174. An objective of this work is to demonstrate that a “Volfilter” exposed to a OAUGDP will have the number of captured microorganisms on its surface reduced by a factor of one million     

Efficient photoconductive terahertz source using line excitation

We report significant improvement in terahertz (THz) power and efficiency using photoconductive sources by use of a spatially extended line source excitation and the trap enhanced field effect that occurs in sources made on semi-insulating GaAs. The combination of high electric fields and reduced screening effects allows 10 microW of THz power to be generated with 14 mW of absorbed optical power, demonstrating nearly 0.1% optical-to-THz conversion efficiency.     

Generation of a uniform high-density microwave plasma for CO2 lasers using orthogonal electric fields

To realize a CO₂ laser using a fast-axial-flow high-output-power microwave discharge excitation, we devised a technology for making the microwave discharge uniform by varying the oscillation direction of an electric field with time. We also verified the effectiveness of this technology. As a result, we succeeded in increasing the discharge uniformity to 70% of the laser-tube cross-sectional area and realized a high laser output power and a high laser efficiency. In the case of a microwave input power of 1450 W, a maximum laser output power of 273 W and a laser efficiency of 18.8% were achieved; in the case of a microwave input power of 1070 W, a laser output power of 214 W and a laser efficiency of 20.0% were achieved. At the time of maximum output power, a high input power density of 280 W/cm³, which is approximately 20 times that in a dc discharge method, was achieved. Thus, a high-output-power microwave-discharge-excited CO₂ laser has become feasible. PACS 42.60.By; 52.80.Pi     

Hybrid correlator employing a chirp-encoded binary phase-only filter

A novel correlator architecture is described that is similar to the VanderLugt correlator (VLC) but differs because the input Fourier transform (FT) is performed electronically rather than optically. We present results in which the FT's are reduced to binary phase-only filters (BPOF's); the required multiplication of the input and the reference FT's (performed optically in the VLC) is performed electronically simply by use of a single XOR logic gate. The problematic zero order and symmetric correlation peak are shown to be removed by use of a chirp-encoded BPOF.     

Heat source reconstruction from noisy temperature fields using a gradient anisotropic diffusion filter

This paper presents a post-processing technique for noisy temperature maps based on a gradient anisotropic diffusion (GAD) filter in the context of heat source reconstruction. The aim is to reconstruct heat source maps from temperature maps measured using infrared (IR) thermography. Synthetic temperature fields corrupted by added noise are first considered. The GAD filter, which relies on a diffusion process, is optimized to retrieve as well as possible a heat source concentration in a two-dimensional plate. The influence of the dimensions and the intensity of the heat source concentration are discussed. The results obtained are also compared with two other types of filters: averaging filter and Gaussian derivative filter. The second part of this study presents an application for experimental temperature maps measured with an IR camera. The results demonstrate the relevancy of the GAD filter in extracting heat sources from noisy temperature fields.     

Thermal coherence tomography using match filter binary phase coded diffusion waves

Energy transport in diffusion-wave fields is gradient-driven and therefore diffuse, yielding depth-integrated responses with poor axial resolution. Using matched-filter principles, we propose a methodology enabling these parabolic diffusion-wave energy fields to exhibit energy localization akin to propagating hyperbolic wave fields. This not only improves axial resolution but also allows for deconvolution of individual responses of superposed axially discrete sources, opening a new field of depth-resolved subsurface thermal coherence tomography using diffusion waves.     

应用复振幅滤波器实现高斯光束均匀化

激光束的光强分布为高斯分布。在激光应用的许多领域，要求光束的光强为均匀分布。本文提出了一种利用复滤波器实现高斯光束均匀化的新方法。给出了复滤波器的制作方法和实验结果。实验表明，该方法是一种能量转化率较高、容易实现、均匀化程度较为理想的高斯光束均匀化的方法。     

Generation and amplification of sub-picosecond pulses using a frequency-doubled neodymium YAG pumping source

Stable, tunable, sub-picosecond pulses have been obtained by synchronously pumping a Rhodamine 6G dye laser with a frequency-doubled CW modelocked neodymium YAG laser. Careful attention has been paid to minimize amplitude and timing instabilities, resulting in dye laser pulses shorter than 500 fs. The main advantage of this new pumping source over current synchronously pumped dye lasers is that it is particularly well suited to short pulse amplification. Using this technique amplification of 2 × 10⁶ has been achieved.     

一种LED照明光源均匀度设计

为了满足数字摄像法能见度测量仪均匀光源的要求,提高半导体发光二极管照明的均匀性,该文提出一种基于数字图像分析技术的设计方法。首先测量单颗LED在模组区域的亮度分布,进而拟合分布函数,再运用多颗LED亮度叠加原理,计算出不均匀度最小的多颗LED阵列方式,或固定均匀度对应的最佳尺寸。对仿真数据和实测数据进行对比分析,结果表明,该文计算出的LED阵列方式,与单边阵列相比,均匀度显著提高,最高可达95%以上。     

Robust tracking of moving sound source using multiple model Kalman filter

In this paper a novel method for tracking an active speaker in a noisy and reverberant environment by means of a spatially distributed microphone array is presented. Firstly, a sound source localization algorithm based on time delays of arrival (TDOA) in microphone pairs provides observed position estimates. Then these remarkably noisy estimates are filtered by a multiple model Kalman filter (MMKF) in order to obtain a smoothed trajectory of the speaker’s movement. Compared with the traditional Kalman filter (KF), simulated results prove the MMKF is more robust and effective in noisy environments.     

Robust tracking of moving sound source using scaled unscented particle filter

Tracking an active sound source involves the modeling of non-linear non-Gaussian systems. To address this problem, this paper proposed scaled unscented particle filter (SUPF) algorithm for tracking moving sound source. The particle filter part of the SUPF provides the general probabilistic framework to handle non-linear non-Gaussian systems, and the scaled unscented Kalman filter (SUKF) part of the SUPF generates better proposal distributions by taking into account the most recent observation. Meanwhile, models used in SUPF algorithm were also explored for the sound source motion, observation and the likelihood of the sound source location in the light of the Langevin process. Compared with the conventional PF approach, the simulated results demonstrated that the SUPF algorithm had superior tracking performance.     

Generating a uniform transverse distributed electron beam along a beam line

It has been reported that transverse distribution shaping can help to further enhance the energy extraction efficiency in a terawatt, tapered X-ray free-electron laser. Thus, methods of creating and keeping an almost uniform transverse distributed(UTD) beam within undulators are required. This study shows that a UTD electron beam can be generated within evenly distributed drift sections where undulators can be placed, by means of octupoles and particular optics. A specific design is presented, and numerical simulations are performed to verify the proposed method.     

Optimization of a binary transcoding single filter used for character recognition

We propose a new type of optical filter for character recognition. We intend to show that a unique optimized filter is suitable for binary transcoding of an alphabetical set. The unique filtering consists of a multiplexing from a superposition of holographic filters. Synthesis can be implemented either by analog holography or by numerical holography. A verification obtained from a limited alphabet is presented.     

Generation of electron beams in a multicathode secondary-emission source

A study is made of the generation of electron beams in a system consisting of eight secondary-emission cathodes arranged at regular intervals in the azimuthal direction inside a coaxial cylindrical anode in crossed electric and magnetic fields. In this system with an azimuthally nonuniform electric field, secondary-emission multiplication of electrons is realized and beam generation is achieved. With a cathode voltage of ∼37 kV and a magnetic field of ∼3000 Oe, the total current of all the beams amounts to ∼35 A, the microperveance of each beam being ∼0.7 μA/V^3/2.     

Multi-wavelength fiber source based on double-pass superfluorescent fiber source and a reflection Mach-Zehnder filter

A spectrum-sliced multi-wavelength fiber source (SS-MWFS) based on double-pass superfluorescent fiber source (SFS) with a reflection Mach-Zehnder filter (RMZF) as the reflected comb filter is demonstrated.With backward pumped configuration, MWFS with 50 wavelength channels of extinction ratio (ER) of 16.7 dB is obtained over the almost total C-band gain region. Total output power of the MWFS is 16.2 mW which shows that a power of about 0.3 mW of per channel is achieved. The SS-MWFS with forward pumped configuration is also discussed for comparing. The backward pumped configuration can provide a larger output power while only a little smaller ER than that of the forward pumped configuration.     

Enhancing the capabilities of binary phase only filter

In this paper, we demonstrate that the capabilities of a binary phase-only filter (BPOF) can be enhanced to identify targets irrespective of rotation, scale or the imaging spectral band by utilizing the concept of log-polar transform and image fusion. Till date, BPOFs have been considered to be the simplest of all filters and incapable of identifying distorted images or images of different spectral bands like the visible or infrared (IR) bands. The novelty of this work lies in the approach adopted to demonstrate that a BPOF is equally capable of distortion-invariance like any other distortion-invariant complex matched filter. This is done by suitably fusing the images of visible and IR bands and then taking the log-polar transformation of the fused image to synthesize the BPOF. A single BPOF is thus sufficient to identify (0-360)° in-plane rotated images, (50-190)% scaled images, combination of rotation and scale changes of the target, noisy image of both the visible and IR spectral bands. A further enhancement of the correlation peak intensity (CPI) is achieved by modifying this BPOF with Mexican-hat wavelet. The designed filter was implemented in the hybrid digital-optical correlation scheme. Correlation peak intensity and peak correlation energy (PCE) have been calculated as metrics of goodness of the proposed approach. Experimental results have been presented.