Optimized pulse source employing an externally injected gain-switched laser diode in conjunction with a nonlinearly chirped grating

In this paper, we demonstrate the generation of transform-limited short optical pulses, which display excellent spectral and temporal qualities by employing a novel technology, based on an externally injected gain-switched laser in conjunction with a nonlinearly chirped grating. Using this technique, 3.5-ps optical pulses exhibiting a time-bandwidth product (TBP) of 0.45 are generated, which are suitable for use in high-speed 80 Gb/s optical time-division multiplexing (OTDM) communications systems. The numerical integration of a set of rate equations using suitable parameters for the devices used in the experiments were carried out to further confirm the feasibility of the proposed method for developing an optimized pulse source for high-speed photonic systems.     

Self-starting 6.5-fs pulses from a Ti:sapphire laser using asemiconductor saturable absorber and double chirped mirrors

We demonstrate self-starting 6.5-fs pulses from a Kerr-lens-mode-locked Ti:sapphire laser with an average output power of 200 mW at a pulse repetition rate of 86 MHz. We have achieved a mode-locking buildup time of only 60 μs, using a broad-band semiconductor saturable absorber mirror to initiate the pulse formation. The dispersion has been compensated with a prism pair in combination with improved double-chirped mirrors. The prism pair allows for the flexible adjustment of both the duration and the center wavelength of the pulse. The double-chirped mirrors show a high reflectivity better than 99.8% over the full bandwidth of 300 nm and a controlled group delay over more than 250 nm. The choice of a proper output coupler turns out to be critical for ultrashort pulse generation directly from the laser     

Is efficiency of gain generation in Li III 13.5-nm laser with0.25-μm subpicosecond pulses the same as with 1 μm?

The main goal of this paper is to present experimental results on comparison of lasing efficiency for Li III 13.5 nm (2-1 transition) line in LiF microcapillary plasmas using 0.25 and 1 μm subpicosecond pumping lasers. A formula for soft X-ray laser efficiency calculation is presented and used for such comparisons. The results for discharge created preplasma in L=4 mm and L=14 mm microcapillaries are also presented and compared with the results for laser created preplasma     

Stability of a pulse converter with PWM-2

A microelectronic control system based on a bilateral pulse width modulator-2 (PWM-2) is described. Stability conditions for the current loop with a proportional integral (PI) regulator are grounded by the linear pulse model and those conditions are used to calculate and analyze system’s stability areas depending on its key parameters.     

Seeding of an eleven femtosecond optical parametric chirped pulse amplifier and its Nd/sup 3+/ picosecond pump laser from a single broadband Ti:Sapphire oscillator

We demonstrate direct simultaneous seeding of a few-cycle optical parametric chirped pulse amplifier (OPCPA) in the 700-1000-nm spectral range, and of a Nd:YLF amplifier emitting 30-ps pulses at 1053 nm by use of a chirped-mirror 6-fs Ti:sapphire oscillator. This approach of employing a single master oscillator to drive two power amplifiers simplifies the pump laser design and is applied to eliminate the timing jitter between the seed and the pump pulses in the OPCPA chain. We show that 10 mJ fundamental picosecond pump pulses with the intensity contrast in excess of 10/sup 4/ relative to the nanosecond Q-switched background can be achieved with the seed intensity available in the edge of the oscillator spectrum around 1053 nm. Cross-correlation measurements between the picosecond pump and femtosecond oscillator pulses reveal no traceable timing jitter between the OPCPA pump and seed pulses. The estimated long-term jitter of 0.3 ps is attributed to the thermal expansion of the cavity of the Nd:YLF regenerative amplifier.     

Interface trap generation and hole trapping under NBTI and PBTI in advanced CMOS technology with a 2-nm gate oxide

This paper gives an insight into the degradation mechanisms during negative and positive bias temperature instabilities in advanced CMOS technology with a 2-nm gate oxide. We focus on generated interface traps and oxide traps to distinguish their dependencies and effects on usual transistor parameters. negative bias temperature instability (NBTI) and positive bias temperature instability in both NMOS and PMOS have been compared and a possible explanation for all configurations has been suggested. Recovery and temperature effect under NBTI were also investigated showing different behaviors of the two components.     

Power spectral density of a UWB signal with discrete quantized pulse positions

The FCC specification for ultra-wideband (UWB) emissions states that the effective isotropic radiated power (EIRP) cannot exceed 41.3 dBm per 1 MHz bandwidth in the frequency region of 3.1 to 10.6 GHz. Hence, to achieve adequate transmit power in a UWB data link it is necessary to use a wide-bandwidth modulation scheme. This requirement presents a pair of technical challenges which are addressed in this paper. The first challenge is to realize a wide-bandwidth radiated transmitter pulse shape which adequately covers the UWB band from 3.1 to 10.6 GHz. The second challenge is to structure the modulation such that the discrete line component of the power spectral density (PSD) of the transmitted signal is minimized. This is necessary as the discrete spectral components are essentially wasted power and limit the output transmitted power due to the FCC EIRP mask. In this paper the radiated EIRP of a UWB signal based on pulse position modulation (PPM) is explored. Previous researchers have derived the PSD under the supposition that the PPM pulse delay is continuous. However, simpler and more insightful expressions are possible for the PPM PSD if the pulse delays are restricted to quantized steps, as is assumed in this paper. A network-analysis approach for determining the EIRP of the unmodulated radiated pulses is given based on spectral measurements of an experimental UWB transceiver pair. These EIRP characteristics are applied to the derived equations for the continuous and discrete portions of the PSD of the UWB signal. From this, insights emerge into optimum PPM transmitter implementation that maximizes transmit power and minimizes power losses due to the discrete spectral lines. As demonstrated in this paper, such optimization necessitates the joint design of the UWB transmitter radiated pulse shape and PPM structure.     

脉冲注入法和单端故障行波法相结合的直流输电系统接地极线路故障测距

分析了直流输电系统在单极运行方式下,接地极线路故障暂态行波和外部注入脉冲信号在接地极线路上的传播过程。以此为基础,提出一种将脉冲注入法和单端故障行波法相结合的接地极线路故障测距方案。首先通过在换流站直流中性母线处监测接地极线路故障暂态行波识别线路是否发生故障,在线路故障暂态过程结束后从中性母线向线路注入脉冲信号。根据脉冲注入法得到初步测距结果,并以此确定故障区段。然后,根据确定的故障区段,进一步用单端故障行波法再次获得测距结果。最后,对两次测距结果取平均值,作为最终测距结果。以PSCAD/EMTDC为仿真平台,搭建了直流输电系统在单极运行方式下的接地极线路故障测距仿真模型。并借助Matlab对仿真波形数据进行分析,表明所提出的接地极线路故障测距方案是可行的。     

等离子体反应器的改进及其与脉冲电源间的匹配

采用一种基于闸流管开关、Blumlein脉冲形成网络和脉冲变压器技术的高压脉冲电源,以模拟甲苯废气为净化对象,在线板式反应器内进行了结构改进试验.考察了线板式反应器内的电晕线间距及在反应器内引入的折流板、阻挡介质陶瓷板和催化剂对甲苯去除率的影响,分析了反应器峰值阻抗与电源的输出特性阻抗的匹配关系,为优化反应器设计及与电源匹配提供了基础数据.结果表明:反应器设计中,电晕线间距和电晕线与极板间距之比以0.8左右较好;反应器内加折流板,甲苯的去除率有所提高;负载Mn催化剂的陶瓷板阻挡反应器的去除率及能量利用率最高,陶瓷板阻挡的次之,无阻挡的最低;峰值电压增大,反应器的峰值阻抗降低,其与脉冲电源的输出特性阻抗比值β趋近1,电源的能量效率相应增大,最大可达92%.     

Generation of high-energy (0.3 μJ) short pulses (<400 ps)from a gain-switched laser diode stack with subnanosecond electricalpump pulses

Record pulse energy (E~0.3 μJ) is reported for a gain-switched laser diode stack with subnanosecond electrical pump pulses. Pulsewidths near 100 ps are seen to be feasible. A detailed time-resolved analysis of emitted near-field patterns is presented, which provides guidelines for further improvements in time performances. A stack design for pulsed laser diodes of high energy is discussed     

考虑声-振模态结合的抽水蓄能机组轴承故障诊断

为解决抽水蓄能机组轴承磨损故障难以监测和识别的问题,提出一种结合声振数据的双模态神经网络机组轴承诊断模型。首先分析了抽水蓄能机组声振特性,融合相似软阈值对奇异值分解去噪方法进行改进,有效消除非接触式传感器固有噪声干扰。其次提出逆巴克频谱变换方法,并结合巴克频谱变换和格拉姆角和场变换等特征工程技术,提取机组轴承的声纹和振动特征图。通过融合相对位置编码的自注意力机制和深度可分离卷积,建立特征图传递网络。同时运用多头自注意力机制和双向长短期记忆网络搭建了时序数据传递网络,并以平行网格架构构建了机组轴承故障诊断模型。实验对比分析表明,所提方法具有较高的故障识别准确率,为抽水蓄能电站机组轴承监测问题提供了有效的解决途径。     

如何对低占空比脉冲信号进行测试和分析(上)

随着对低占空比信号(如激光脉冲、雷达脉冲等),以及偶发性或间歇性信号的测试要求越来越高,示波器使用传统方法测试这类信号难以达到测试感兴趣信号的需求。针对这类信号,本文回顾了实时示波器传统测试方法以及缺点,同时详细介绍了利用FastFrame分段存储技术的测试方法,并对这种测试方法的测试误差进行分析,最后是一些测试实例。     

Specifics of running dynamics and energy diagrams of a pulse electromagnetic drive with shunt- and cascade-connected excitation windings

The prospective applicability of powerful short-stroke electromagnetic drives in vibro-pulse technologies is observed. The influence of working gap nonuniformity and magnetic circuit saturation on energy diagrams, generated force, and operation speed for shunt- and cascade-connected excitation windings is analyzed.     

Imaging gray brain matter with a double-inversion pulse sequence to suppress CSF and white matter signals

The design of a double-inversion recovery (DIR) sequence, to selectively image gray brain matter, is described. A suitable choice of inversion times allows the cerebrospinal fluid (CSF) and white matter to be suppressed, to image the cortex alone. Consistently good results were achieved in a group of normal volunteers using the same inversion times throughout. The DIR sequence was found give clear delineation of the complex folds of the cerebral cortex.     

Broadband complex dielectric constants of water and sodium chloride aqueous solutions with different DC conductivities

Broadband dielectric constant measurements in the frequency range between 40 Hz and 50 GHz of pure water, tap water, and sodium chloride aqueous solutions with different DC conductivities up to 5 S/m were conducted. The measurements were done using an impedance analyzer for the frequency range 40 Hz to 110 MHz and a vector network analyzer for 10 MHz to 50 GHz. The results show that the dielectric constant decreases with the increase in DC conductivity and is dependent on the frequency. The dielectric relaxation of water with a constant dielectric loss peak was also observed. The frequency dependence of the conductivity is also large. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

特高压工程的DCC800直流保护与控制系统配合逻辑分析

在锦屏—苏南、向家坝—上海特高压直流输电工程中直流保护和控制系统采用DCC800硬件平台,直流保护与控制系统通过eTDM总线完成数据交换,包括所有的保护动作信号。对直流保护和控制系统的配合逻辑进行了详细的阐述和研究,包括直流保护与控制的硬件组成,直流保护与控制系统间的信号交换,直流控制系统对保护信号的处理,以及控制系统软件中"三取二"选择逻辑、保护矩阵的配置以及不同类型的动作响应等;此外,对DCC800与西门子技术的控制保护系统进行了比较分析。根据工程实际运行状况来看,采用该设计理念的直流控制和保护系统运行稳定、可靠。     

Optimal pulse patterns of a nine-phase voltage source PWM inverter for use with a triple three-phase wound ac motor

The authors have already described the nine-phase inverter driving system providing both the triple three-phase voltage source inverter with 180-deg conducting period and the ac motor windings with triple three-phase construction. The nine-pulse inverter driving system used three small-capacity three-phase coupling reactors having special windings for current balance and reduction of higher harmonics. In addition, for voltage control, current balance, and waveform improvement, optimal PWM pulse patterns were applied to the six-phase inverter driving system using a three-phase coupling reactor to provide double three-phase construction. In the system based on the mode in the title, the PWM control was applied to the nine-phase inverter driving system described in the foregoing. The coupling reactors in the system balance the fundamental currents of three sets of three-phase inverters and also absorb higher harmonic voltages other than 18p±1 (p = 1, 2, …) orders. The optimal pulse patterns found by the approach to make the performance index minimum using the Lagrange multiplier method can be applied to the PWM to reduce the higher harmonic currents greater than those calculated by the modulation method comparing the sinusoidal signal wave with triangular carrier signal. This system can have a larger capacity than the six-phase PWM inverter driving system in which coupling reactors absorb higher harmonic voltages other than the 12p±1 orders and also improve output current waveforms. In addition, the system includes the capacity of coupling reactors slightly larger than the six-phase PWM inverter driving system but enables operation with smaller torque ripples and electromagnetic noises in low- to high-frequency ranges.     

Design and construction of a TW-class 12-fs Ti:Sapphire chirped-pulse amplification system

We describe a design and a construction of a TW-class 12-fs Ti:sapphire chirped-pulse amplification system. We developed a broadband pulse stretcher, a broadband gain-narrowing compensator, broadband high-energy mirrors, high-energy dichroic chirped mirrors, a dispersion compensator, and a broadband pulse compressor for /spl sim/10-fs pulse generation. Utilizing these optical devices, we demonstrated a generation of 12-fs pulses from a 10-Hz-repetition-rate Ti:sapphire chirped-pulse multipass amplifier system and a 1-kHz-repetition-rate Ti:sapphire chirped-pulse regenerative amplifier system. Optimized designs of broadband Ti:sapphire amplifiers with multilayer gain-narrowing compensators and an adaptive dispersion compensator with a spatial light modulator contribute to the shorter pulse amplification.     

Production and probing of atomic wavepackets with ultrafast laser pulses: applications to atomic and molecular dynamics

We demonstrate that atomic wavepackets can serve as sensitive detectors for investigating atomic and molecular dynamics. In concert with parametric four-wave mixing, the interference between coherent superpositions of atomic excited states produced by ultrafast (/spl sim/150 fs) pump and probe pulses provides a new and powerful tool with which fundamental processes, such as molecular dissociation and Rydberg-Rydberg atomic collisions, can be observed with the extraordinary sensitivity afforded by a coherent nonlinear optical process. Experiments are described in which the dissociation of an electronically excited molecule (Rb/sub 2/) and the distribution of atomic fragments into excited states spanning >10 000 cm/sup -1/ are observed. Also, resonant collisions between Rb atoms in the 7s and 5d states are detected by monitoring the shift in the frequency of an atomic wavepacket induced by the dipole-dipole interaction.     

GPS与微机试验仪相结合的成功经验

针对高频保护在生产调试中的迫切需要,本着经济和实用的基本原则,利用GPS接收机和微机试验仪开发了高频保护双端对调装置,并从理论和实践上予以详述,以达到高频保护双端对调装置在继电保护生产维护中推广应用之目的.