Prebreakdown current and charge flow in long positive point-plane gaps with impulse-voltage waves having times to crest in the range 15?1200 ?s

Measurements of prebreakdown current and charge flow in long positive point-plane gaps have shown a critical charge injection which is a function of time to peak of the voltage wave. With increasing time to peak, the pattern of current flow changes from a single large-amplitude pulse to a series of discrete pulses of lower amplitude but of similar duration.     

脉冲空心阴极放电管的光电流光谱研究

研制了一台可调整脉冲电源 ,并用于空心阴极放电管读取 5L6 16 90 0 7M7的光电流光谱。调整脉冲电源的脉冲宽度、脉冲频率、直流偏压以及输出电压等参数 ,记录读取光电流信号及光电流光谱 ,并分析比较所得结果     

The influence of magnetic fields on dielectric surface flashover

The influence of low-amplitude magnetic fields, in a variety of configurations, on pulsed dielectric surface flashover has been investigated. These variations include DC magnetic fields; pulsed magnetic fields simulating conditions for magnetic self-insulation; and different environments (vacuum, ambient, gas, plasma), geometries, dielectric materials, and orientations of the magnetic field. For field amplitudes of 0.3 T, typically a doubling of the flashover voltage is observed, if the E×B drift is away from the surface. For flashover in vacuum, it is sufficient to place permanent magnets in the cathode vicinity to increase the flashover voltage. The observations are consistent with the saturated surface secondary avalanche model and electron-induced gas desorption. The pulse shape of light emission during the prebreakdown phase depends on the orientation and amplitude of the magnetic field and shows that the electron trajectories above the surface are altered by magnetic fields     

Perturbations of conduction in liquids by pulsed laser-generatedplasma

The observation of optical perturbations of electrical conduction processes in aqueous solutions by laser-produced plasmas is reported. The irradiation of a liquid in a conduction cell with a pulsed tightly focused Q-switched Nd⁺³:YAG laser produces plasma that modifies the conductivity of the medium and generates a voltage pulse that can be recorded at the cathode using the same procedure, as in optogalvanic spectroscopy. At low voltages across the cell, this electrical pulse is a positive voltage change, which returns to the equilibrium potential in times much longer than the laser pulse duration. Increasing the cell voltage, this electrical pulse becomes a damped oscillation. Beyond those values, the pulse inverts its sign at the cathode. Results also show that there is a change in cell conductivity in a long-term regime. An interpretation with a first-order model suggests that this behavior could be explained as an excess of ionization, followed by diffusion controlled by recombination in the bulk of the solution     

光电流光谱技术与原子荧光法联用测定激光波长

激光波长仪可在一定精度内测定激光波长,但在激光光谱学和激光分离同位素的应用研究中,不能保证测得的波长已与原子的某一跃迁共振。而光电流光谱技术恰好具有及时地反映这种共振的性能,激光激发原子荧光法的应用又为复杂原子谱线的认定提供准确可靠的依据。我们联用这两种技术简便快速而又准确无误地分别测定了与铀、镧原子一些非精细结构高分辨谱线中某一成分共振的激光波长。     

Laser-triggered dynamic breakdown of gases and laser-induced prebreakdown signals

Dynamic breakdown of Ne and Ar gases biased to the prebreakdown stage, with and without absorption of very short duration incident N2laser pulses, is studied. Effects of bias and incident laser intensity are seen to be complementary. Laser illumination of the interelectrode gap causes gas breakdown at the cathode to take place at a faster rate and at lower breakdown threshold bias than without the illumination. Breakdown pulse shape varies according to gas composition and bias, and is much different from simple nonbreakdown "prebreakdown" responses to the laser pulses. The prebreakdown signals are attributed to photon-enhanced ionization in the focal volume between the electrodes, while the laser-triggered breakdown pulses are attributed to photon-enhanced excitation and diffusion of such neutral atoms to the high field gradient region near the cathode, where cascade ionization collisional effects are amplified.     

Frequency locking of 1.5 μm DFB laser diode to a neon indicatorlamp using the optogalvanic effect

Many proposed applications for optical wavelength division multiplexing (WDM) networks and coherent optical communication systems require the use of a frequency-stabilized optical reference. The feasibility of producing such a reference by using the optogalvanic effect to frequency-lock a distributed feedback laser (DFB) to the atomic absorption line of a low-cost neon indicator lamp is discussed. Frequency fluctuations of the free-running laser were reduced by more than a factor of 25 to ±16 MHz. This is the first reported use of a miniature indicator lamp to frequency-lock a semiconductor laser in the 1.5 μm spectral window     

Graphene‐Assisted Epitaxy of Nitrogen Lattice Polarity GaN Films on Non‐Polar Sapphire Substrates for Green Light Emitting Diodes

Lattice polarity is a key point for hexagonal semiconductors such as GaN. Unfortunately, only Ga‐polarity GaN have been achieved on graphene till now. Here, the epitaxy of high quality nitrogen‐polarity GaN films on transferred graphene on non‐polar sapphire substrates by molecular beam epitaxy is reported. This success is achieved through atomic nitrogen irradiation, where C? N bonds are formed in graphene and provide nucleation sites for GaN and leading to N‐polarity GaN epitaxy. The N‐polarity characteristics are confirmed by chemical etching and transmission electron microscopy measurement. Due to the higher growth temperature of InGaN at N‐polarity than that at Ga‐polarity, green light emitting diodes are fabricated on the graphene‐assisted substrate, where a large redshift of emission wavelength is observed. These results open a new avenue for the polarity modulation of III‐nitride films based on 2D materials, and also pave the way for potential application in longer wavelength light emitting devices.     

Millimeter wavelength radiation emission during dielectric aging

The current-voltage characteristic for a “metal — thick insulator — metal” structure has been investigated by applying high voltage impulses on a variety of industrial insulators. It appears that, in the high field regime (～1MV/cm) S-type Negative Differential Conductance may occur, leading to self sustained conductivity oscillations possibly originating in field dependent carrier mobility. The phenomenon is associated with radiation emission during thermalization of hot electrons. Measurements have established the presence of millimeter wavelength radiation during prebreakdown and breakdown stages. The radiation emission intervals within a high-voltage pulse application and response have also been investigated.     

Frequency-locked diode laser for interferometric sensing systems

Interferometric sensors for slowly varying measurands, such as temperature or pressure, require a long term frequency stability of the source. The authors describe a system for frequency locking a laser diode to an atomic transition in a hollow cathode lamp using the optogalvanic effect     

The optimization of the multi-atmospheric Ar-Xe laser

The quasi-steady-state conditions of the multi-atmospheric e-beam sustained Ar-Xe laser are investigated. It is observed that the duration of the stationary period depends on the e-beam current, discharge power deposition, and gas pressure. The laser efficiency can be as high as 8%. Beyond the stationary period the efficiency drops. The pulse energy with optimum efficiency depends strongly on the gas pressure. The maximum discharge efficiency of 5%-6% is at high pressure not sensitive to the input power. The best results are obtained for 4 bar with a discharge input power of 8 MW/l. The pulse duration with corresponding output energies is 12 μs with 10 J/l and 16 μs with 16 J/l for e-beam currents of 0.4 and 0.9 A/cm², respectively. An analysis of the quasi-steady-state conditions that include the effects of electron collision mixing and atomic quenching is presented. The effects of output power saturation by the fractional ionization and atomic collisions are in agreement with the observations. The analysis clarifies the optimum performance conditions     

Growth of GaN on Buffer Layers with Different Polarities by Hydride Vapor-Phase Epitaxy

This paper reports the properties of GaN grown by the hydride vapor-phase epitaxy (HVPE) technique on buffer layers with different polarities. The N-, mixed-, and Ga-polarity buffer layers were grown by molecular-beam epitaxy (MBE) on sapphire (0001) substrates; then, thicker GaN epilayers were grown on these by HVPE. The surface morphology, structural, and optical properties of these HVPE-GaN epilayers were characterized by atomic force microscopy (AFM), x-ray diffraction (XRD), scanning electron microscopy, and photoluminescence (PL) spectroscopy. The results indicate that the crystallinity of these HVPE-GaN epilayers depends on the polarity of the buffer layer.     

Frequency-locked 1.3- and 1.5-μm semiconductor lasers forlightwave systems applications

A simple technique for frequency-locking 1.3- and 1.5-μm lasers to an excited-state atomic transition of noble gases using the optogalvanic effect is described. Many of the atomic transitions useful for these spectral regions are tabulated. The performance of frequency-locked lasers under direct frequency modulation is analyzed. It is shown that neither the frequency stability nor the receiver sensitivity shows any serious degradation when a frequency-locked laser is used in a frequency shift keying (FSK) transmission experiment     

场电离检测的Cs原子共振滤波

报道一种场电离检测的Ｃｓ原子共振滤波方案。理论预计：原子系统的固有线宽约为６０ＭＨｚ，响应时间为１ｎｓ，量子效率为９９％；初步实验测得（包括实验系统因素）响应时间为１２０ｎｓ，最小可探测光强为１０ｎＪ。     

高重复率脉冲可调谐染料激光器在光谱学上的应用

本文报道利用高重复率脉冲可调谐激光器作光源所进行的光谱实验,获得脉冲激光作用下Ne的敏化荧光光谱、Ne-Cu灯的光电流信号的时间积分谱及Kr-U灯的光电流光谱。     

放电管内铷原子光电流特性及强度的径向分布

1.用电参数来探测光的效应,不但简单、效率高,而且避免了光探测存在的散射光影响等问题,还非常适合于研究难气化、腐蚀性强及高激发电位样品的性质,所以近十年来已经进行了大量理论和实验研究.在原子分子光谱、等离子体诊断、痕量元素分析、火焰燃烧等许多科学和技术领域,已经得到了广泛的应用.对于多数碱原子的光电流效应,已经有了不少研究,唯独铷原子的光电流效应却缺少研究报道.我们用射频放电方法,成功地测量了纯铷放电泡的光电流效应.本文较详细地报告了铷原子光电流特     

超强激光与等离子体相互作用中的自生磁场及三维模拟

用3维粒子模拟程序对超热电子在等离子体靶表面中向前传输时所激发的电流密度,电场和磁场的发展过程进行模拟研究。数值模拟表明,在线性强激光作用下,由于电子初始时刻的无规则热运动,在等离子体临界表面上激发不稳定性,而不稳定性随时间发展和激光功率的进一步深入到等离子体内部,最终使等离子体表面处激发饱和自生磁场,饱和自生磁场对激光有质动力推开电子时所形成的高能电子运动产生抑制作用.通过该研究寻找相对论效应条件下的自生磁场,并为进一步开拓其在高能离子束的应用提供理论和技术上的指导。     

Application of reflection and diffraction techniques to the analysis of an EMP simulator

The response of a parallel-plate transmission-line electromagnetic pulse (EMP) simulator to continuous wave excitation in the very high frequency (VHF) region is analyzed. A reasonably accurate prediction of response irregularities measured in an operational EMP test facility is obtained using a combination of geometrical optics and geometrical diffraction theory. The analysis predicts that multiple internal reflections were primarily responsible for observed irregularities at the measurement positions. While an analysis based upon optical techniques involves different approximations and assumptions than alternative methods, such as the method of moments, the optical approach was found to be more practical in the VHF regime and, perhaps more importantly, allowed identification of the dominant physical mechanisms which cause deviations from the ideal field quality desired of the facility in the VHF region. Based upon these calculations, the simulator was modified to reduce internal reflections, and subsequent measurements have confirmed the usefulness of the theoretical predictions.     

真空中电极间隙的预击穿特性研究

本文对真空中电极间隙和真空灭弧室的预击穿特性进行了研究，分析了影响真空中预击穿特性的因素。     

Effect of externally applied pressure on zinc oxide varistors

A study of the effect of uniaxial pressure on the I-V response of zinc oxide varistors has shown a pressure sensitivity in both prebreakdown and breakdown regions. The general observation is that the conductivity increases with pressure, the effect being more pronounced in the prebreakdown region. Data are in general agreement with the phenomenological model given by Schwertz and Mazenko. Data are also treated on the basis of Schottky barrier and tunneling theories. According to this analysis, the barrier height is found to decrease with pressure. At the time this work was performed, M. P. Mathur was a Consultant for the Westinghouse Electric Corporation, Pittsburgh, Pennsylvania.