Emission of a single normal wave by a vertical discrete linear array in the Pekeris waveguide

The problem of emission of a single normal wave by a vertical discrete linear array in the Pekeris waveguide is studied. The array aperture is less than the waveguide thickness. The sound energy is emitted into the discrete and continuous spectra.     

The power pattern of a hydroacoustic array in a waveguide

A definition of the directional pattern of a transmitting hydroacoustic array operating in a waveguide is introduced as the normalized azimuth dependence of the emitted power. Directional patterns of a horizontal linear array and a planar rectangular vertical array are considered as examples.     

Interaction of counterpropagating discrete solitons in a nonlinear one-dimensional waveguide array

We experimentally investigate the interaction of counterpropagating discrete solitons in a one-dimensional waveguide array in photorefractive lithium niobate. While for low input powers only weak interaction and formation of counterpropagating vector solitons are observed, for higher input powers a growing instability results in discrete lateral shifting of the formed discrete solitons. Numerical modeling shows the existence of three different regimes: stable propagation of vector solitons at low power, instability for intermediate power levels leading to discrete shifting of the two discrete solitons, and an irregular temporal dynamic behavior of the two beams for high input power.     

High packing density laser diode stack arrays using Al-free active region laser bars with a broad waveguide and discrete copper microchannel-cooled heatsinks

A high packing density laser diode stack array is developed utilizing Al-free active region laser bars with a broad waveguide and discrete copper microchannel-cooled heatsinks. The microchannel cooling technology leads to a 10-bar laser diode stack array having the thermal resistance of 0.199 ℃/W, and enables the device to be operated under continuous-wave （CW） condition at an output power of 1200 W. The thickness of the discrete copper heatsink is only 1.5 mm, which results in a high packing density and a small bar pitch of 1.8 mm.     

A technique for measuring the sound of a moving tire

A measurement and analysis technique has been developed to determine the narrow band spectra and the radiation patterns of the sound emitted by a moving tire. The sound is measured by a semicircular array of stationary microphones as the tire passes by the array and is recorded on a multi-channel tape recorder. In the analysis procedure corrections are made for effects associated with a moving sound source, such as the non-stationarity of the signal due to the time-dependent transmission path and the Döppler frequency shifts. In this way the power spectra and the radiation pattern of the sound signal are determined as if the receiver were moving with the tire at a fixed distance. A relationship between the Döppler effect and the frequency resolution associated with the finite Fourier transform is presented. This relation is used as a basis for the Döppler correction procedure.     

圆台形超声相控阵列在管材检测中的聚焦声场

针对一种新型的用于钢管横向缺陷检测的圆台形超声相控阵列,提出了计算管内一次波位移场的模型。设计了三维情况下,圆柱界面存在时的时间延迟法则,并在高频近似下,利用瑞利积分法结合稳相法,研究和计算了管材横截面以及纵剖面上的二维声场分布特性。最后详细讨论了圆台形相控阵列中心夹角、阵元宽度及动态阵元数等参数对管材中聚集声场的影响。结果表明,这种模型以及计算方法可以有效地分析圆台形阵列在钢管内的辐射位移场特性,为实际制作这种圆台形阵列提供理论指导。      

应用于PTS装置的多通道X射线二极管阵列谱仪

介绍了用于PTS（初级实验平台）装置上Z箍缩内爆物理实验诊断的多通道X射线二极管（XRD）阵列谱仪原理、性能及主要参数,给出了根据实验结果回推光源辐射能谱的解谱算法。在PTS装置上开展的首轮物理实验中,使用多通道XRD阵列谱仪对Z箍缩产生的等离子体源辐射的软X射线能谱、功率、能量进行测量,给出了测量结果及分析,并与其他参试设备测量结果进行了比较。关键词: Abstract: Key words: ;     

Power emitted by an array of ultra high frequency current modulated semiconductor lasers with global coupling

We report the output power emitted by an array of ultra high frequency current modulated semiconductor lasers (CMSCL) whose elements are mutually coupled in a ring configuration and globally coupled through an external mirror. By varying the coupling strengths, we determine the domain where the in-phase state occurs. The dependence of the output power on the coupling strengths is analyzed. The power increases with the number of lasers and shows an abrupt increase or decrease as the coupling strengths increase. This particular behaviour is related to synchronization.     

Power thresholds of families of discrete surface solitons

We have investigated both theoretically and experimentally the power threshold of discrete Kerr surface solitons at the interface between a discrete one-dimensional (1D) (waveguide array) and a continuous 1D (slab waveguide) AlGaAs medium. Decreasing power thresholds were predicted and measured for soliton trapping at sites with increasing distance from the boundary. The thresholds approached asymptotically the power required for a discrete soliton of equivalent width in an infinite lattice. The minimum threshold coincided with a minimum in the interchannel coupling strength.     

Caustic design in periodic lattices

We study curved trajectory dynamics and design in discrete array settings. We find that beams with power law phases produce curved caustics associated with the fold and cusp type catastrophes. A parabolic phase produces a focus that suffers from spherical aberrations. More important, we find that by designing the initial phase or wavefront of the beam we can construct trajectories with pure power law caustics as well as aberration-free focusing of discrete waves.     

Laser-diode-pumped phosphosilicate-fiber Raman laser with an output power of 1 W at 1.48 mum

An all-fiber 1.48-mum generator based on a laser-diode-pumped Yb-doped double-clad laser and a cascaded Raman wavelength converter has been developed. Second-order Raman Stokes radiation was generated in a phosphosilicate-fiber resonator formed by two pairs of Bragg gratings. A slope efficiency of the Raman converter of 48% with respect to the power emitted by the double-clad Yb laser has been achieved. We obtained an output power of 1 W at a slope efficiency of 34% with respect to the laser-diode array power, with a total optical-to-optical efficiency of 23%.     

Electron temperature diagnostics of aluminium plasma in a z-pinch experiment at the ＂QiangGuang-1＂ facility

<正>Two curved crystal spectrometers are set up on the "QiangGuang-1" generator to measure the z-pinch plasma spectra emitted from planar aluminum wire array loads.Kodak Biomax-MS film and an IRD AXUVHS5# array are employed to record time-integrated and time-resolved free-bound radiation,respectively.The photon energy recorded by each detector is ascertained by using the L-shell lines of molybdenum plasma.Based on the exponential relation between the continuum power and photon energies,the aluminum plasma electron temperatures are measured.For the time-integrated diagnosis,several "bright spots" indicate electron temperatures between(450 eV～520 eV)±35%.And for the time-resolved ones,the result shows that the electron temperature reaches about 800 eV±30%at peak power. The system satisfies the demand of z-pinch plasma electron temperature diagnosis on a～1 MA facility.     

Source characterization of a subsonic jet by using near-field acoustical holography

In the present study, patch near-field acoustical holography was used in conjunction with a multireference, cross-spectral sound pressure measurement to visualize the sound field emitted by a subsonic jet and to predict its farfield radiation pattern. A strategy for microphone array design is described that accounts for the low spatial coherence of aeroacoustic sources and for microphone self-noise resulting from entrained flow near the jet. In the experiments, a 0.8-cm-diameter burner was used to produce a subsonic, turbulent jet with a Mach number of 0.26. Six fixed, linear arrays holding eight reference microphones apiece were disposed circumferentially around the jet, and a circular array holding sixteen, equally spaced field microphones was traversed along the jet axis to measure the sound field on a 30-cm-diameter cylindrical surface enclosing the jet. The results revealed that the jet could be modeled as a combination of eleven uncorrelated dipole-, quadrupole-, and octupole-like sources, and the contribution of each source type to the total radiated sound power could be identified. Both the total sound field reconstructed in a three-dimensional space and the farfield radiation directivity obtained by using the latter model were successfully validated by comparisons to directly measured results.     

基于场致发射阴极阵列的太赫兹源的物理机理研究

本文对一种基于场致发射阴极阵列(FEA)的太赫兹辐射源的物理机理进行了理论分析和粒子模拟验证. 采用场匹配法分析了器件的高频场结构, 确定π模作为器件的最优工作模式; 利用线性理论分 析了器件的注波互作用过程, 揭示了高频场对FEA阴极发射电流的预调制作用以及电子在阴阳极间隙的渡越时间效应 是器件起振的物理原因; 分析得出了π模起振条件; 粒子模拟结果与理论分析具有较好的一致性.     

Electron temperature diagnostics of aluminium plasma in z-pinch experiment on “QiangGuang-1” facility

Two curved crystal spectrometers are setup on "QiangGuang-1" generator to measure the z-pinch plasma spectra emitted from planar aluminum wire array loads. The Kodak Biomax-MS film and IRD AXUVHS5# array are employed to record time-integrated and time-resolved free-bound radiation respectively. The photon energy recorded by each detector is ascertained by using the L-shell lines of molybdenum plasma. Based on the exponential relation between the continuum power and photon energies, the aluminum plasma electron temperatures are measured. For the time-integrated diagnosis, several "bright spots" indicate electron temperatures between (450 eV～520 eV)± 35%. And for the time-resolved ones, the result shows that the electron temperature reaches about 800 eV±30% at peak power. The system satisfies the demand of z-pinch plasma electron temperature diagnosis on ～1 MA facility.     

Field emission monotron for THz emission

Small-signal negative conductance of a field emission monotron was calculated, which was considerably higher than that of a thermionic monotron due to strong bunching of emitted electrons in a field emission. The amplification constant of 28dB/mm is achieved at THz wave region by applying the monotron to a distributed amplifier and is sufficient to overcome power loss in a transmission line. In addition, a wide band frequency tunable electromagnetic wave source may be developed at THz wave region by providing a low loss microstrip line resonator with field emission array due to the gate voltage dependent phase constant of the line.     

固态有源相控阵快前沿脉冲发射及空间合成

快前沿射频脉冲发射是固态有源相控阵可实现的优势功能。分析了X波段固态有源相控阵实现快前沿射频脉冲发射的必要条件,包括激励传输、功率放大、定时同步和孔径渡越等影响因素及设计要点。相应的分析结论应用于某型X波段固态有源相控阵的样机研制,最终实现了数千个固态有源通道的快前沿射频脉冲的高效空间合成,合成射频脉冲前沿低于5 ns,验证了分析与设计的有效性。     

阳加速器钨丝阵内爆软X光功率辐射特性

介绍了在阳加速器上进行的系列W丝阵Z箍缩物理实验,实验中阳加速器Marx充电电压60 kV,负载电流输出0.85~1.00 MA,电流上升时间75~90 ns（10%~90%）;进行软X光辐射功率测量的主要仪器是软X光闪烁体功率计,其核心部件为对50~1800 eV X光具有平响应特性的蓝光闪烁体。给出了系列W丝阵Z箍缩实验软X光辐射功率测量结果,从软X光辐射输出随丝阵负载参数（包括丝阵直径、长度、丝数）变化关系讨论了钨丝阵内爆辐射特性,给出了阳加速器上各负载参数优化的结果:丝阵直径Ф8 mm,丝阵长度15 mm,丝数24。同时对软X光辐射的空间分布特性进行了初步的探讨,给出了辐射功率在负载的轴向和径向的分布。     

Quantum transitions of a small Josephson junction array

We have experimentally studied a small Josephson junction array in the presence of microwave irradiation. The array has comparable energy scales for single-charge effects and the Josephson effect, resulting in a discrete set of macroscopic eigenenergy levels. Excitation of the array by low-power microwaves is possible at frequencies where the photon energy matches the level spacing. The microwave frequency and amplitude dependence show that the excitation mechanism involves resonant quantum coherent dynamics of the array.     

Evolution of percolating force chains in compressed granular media

The evolution of effective force chains percolating through a compressed granular system is investigated. We compressed an ensemble of spherical particles monitoring the macroscopic constitutive behavior and the acoustic signals emitted by microscopic rearrangements of particles. We applied the continuous damage model of fiber bundles to describe the evolution of the array of force chains. The model provides a nonlinear constitutive behavior in good quantitative agreement with the experimental results. The amplitude distribution of acoustic signals was found experimentally to follow a power law of an exponent delta=1.15+/-0.05, which is in good agreement with the analytic solution of the model.