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Chongcheng Fan Jiangde Peng Jinghui Li Xin Jiang Gengsheng Wu Bingkun Zhou 《Fiber and Integrated Optics》1994,13(3):247-260
A comprehensive model of erbium-doped fiber amplifiers (EDFA) is proposed in this paper, taking exited-state absorption (ESA), amplified spontaneous emission (ASE), background absorption, mode field, and Erbium ion radial distribution into account. Computer programs capable of handling forward, backward, and different wavelength bidirectional pumping are developed. Among other things, it is found that under typical conditions, Gaussian field approximations may cause considerable errors. The optimum V-value for small signal gain is much smaller than that for minimum Gaussian or Desurvire spot size; ASE propagating opposite to the pimp beam can be several times higher than at propagating along the pump beam, resulting in a faster-than-linear decrease of the pump power at its beginning portion. Experimental results of domestic-made erbium-doped fibers pumped by 980 nm and 1480 nm laser diodes are also given. 相似文献
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Theoretical and experimental investigations of quasi-continuous wave diode array side-pumped Yb'YAG slab laser 下载免费PDF全文
An analytical model of quasi-continuous wave (quasi-CW) diode array side-pumped slab laser for Yb:YAG oscillator in long-pulse free-running has been developed based on the CW model. In this model we first introduce a new parameter, pump pulse width, and make the model available for use in the quasi-CW model. We also give an analytical equation of laser delay time to calculate the laser pulse width. A detailed model is also presented for a new structure laser design, taking account of the geometry of Yb:YAG slab. A quasi-CW diode array side-pumped Yb:YAG slab laser is investigated theoretically and experimentally. Experiments yield a quasi-CW output energy up to 20.36 mJ with the laser pulse width of 654.55 μs at 1049 nm when the diode arrays operate at 25 Hz and 1 ms pulse width. The crystal dimensions are 3 mm×8 mm×1 mm and the doping density is 10 at.%. The experimental results are in good agreement with the predictions of the theoretical model. 相似文献
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Novak J.P. Bartnikas R. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1991,19(2):95-101
The voltage breakdown behavior of a plane-parallel gap of 0.48-mm length filled with helium was examined at atmospheric pressure with admixtures of dry air at relative pressures of 0, 10-4, 3×10-4, and 10-3. The initial stages of the breakdown were investigated by means of a quantitative model consisting of the electron, ion, and excited-particle conservation equations and the Poisson equation. The system of equations was solved for an applied voltage of 180 V, at one single partial pressure of the impurities. Two numerical routines were used for the solution: a commercial IMSL subroutine TWODEPEP, and a newly developed method of solution in several fractional steps. The results were compared and found to be in reasonable agreement although the new method indicated a somewhat slower rate of rise, particularly concerning electron density. The new method permits extension of the calculation up to electron densities equal to almost two orders of magnitude above the earlier limit 相似文献
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This paper has presented transparent conductor oxide materials (TCOMs) based microstrip patch antennas with glass substrate and copper ground plane, which have been deeply analyzed in the visible spectrum region in comparison with the practical patch antenna model of indium tin oxide patch with glass substrate and different TCOMs based ground plane. As well as the study have investigated the effect of transparent oxide materials on patch antenna design instead of perfect conductor materials such as copper that has low cost and weight. The tradeoff between optical transparency and electrical conductivity will be evaluated for a range of visible regions. Microstrip transmission line feed method is used to predict the skin effects on a patch antenna and their impact on antenna efficiency, resonance frequency and optical transmission are also described. This study have discussed assessment of these tradeoffs and effect of TCOMs parameters on antenna design. 相似文献
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The radiation characteristics of a two-element array of equilateral triangular patch microstrip antenna on a ferrite substrate
are studied theoretically by considering the presence of bias magnetic field in the direction of propagation of electromagnetic
waves. It is found that the natural modes of propagation in the direction of magnetic field are left- and right-circularly
polarized waves and these modes have different propagation constants. In loss-less isotropic warm plasma, this array antenna
geometry excites both electromagnetic (EM) and electroacoustic plasma (P) waves in addition to a nonradiating surface wave.
In the absence of an external magnetic field, the EM- and P-waves can be decoupled into two independent modes, the electroacoustic
mode is longitudinal while the electromagnetic mode is transverse. The far-zone EM-mode and P-mode radiation fields are derived
using vector wave function techniques and pattern multiplication approaches. The results are obtained in both plasma medium
and free space. Some important antenna parameters such as radiation conductance, directivity and quality factor are plotted
for different values of plasma-to-source frequency. 相似文献
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基于Fraunhofer衍射理论,建立了六角形相干列阵远场分布的理论模型,采用Strehl比和能量集中度作为评价参数,分析了列阵排列方式、振幅、填充因子对远场分布的影响.并由爬山法相位控制技术和六棱台合束器,构建了七阵元光纤相干列阵实验系统.在066填充因子情况下,获得了Strehl比为070、能量集中度为040七阵元合成光束,以及获得了能量集中度分别为045和018的二阵元线阵和四阵元矩形阵合成光束.
关键词:
相干合成
填充因子
能量集中度
Strehl比 相似文献
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当前国内学者对等离子体天线的研究主要集中于柱状天线和反射面天线, 而在国外已有学者以等离子体阵列结构设计了功能多样的智能天线系统. 为了较系统地了解这一新的设计思路, 基于等离子体散射理论对中心单元激励的圆形定向天线阵进行了理论和实验研究. 设计了一个16元等离子体无源振子的圆形天线阵, 实现了天线电磁波单波束和多波束的定向辐射. 通过理论计算和分析, 阐述了天线电磁波单波束和多波束辐射的原理. 通过建立实验系统, 测试了圆形天线阵的定向辐射特性. 实验结果和理论值接近, 说明该等离子体圆形天线阵可以实现天线电磁波的定向辐射和多波束辐射. 另外, 该天线阵还具有快速切换辐射方向、参数快速重构、雷达隐身性良好的优点.
关键词:
等离子体
定向天线阵
单波束
多波束 相似文献
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This study deals with a generic approach for prediction of pulsation suppression with acoustic dampers. Although the theory is valid for any self-oscillating system and for any damper type, the focus in this paper is on suppression of thermoacoustic oscillations using Helmholtz dampers. The developed theory has been validated using a novel experimental method. In thermoacoustics the constructive interference between the heat release and the acoustic field is responsible for growth of acoustic amplitudes. In the newly developed measurement method, this interaction has been mimicked by a feedback excitation using loudspeakers and microphones. Nonlinear time-domain acoustic network simulations are also used to support the analytical and experimental framework. 相似文献
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Many brittle materials, such as single-crystal materials, amorphous materials, and ceramics, are widely used in many industries such as the energy industry, aerospace industry, and biomedical industry. In recent years, there is an increasing demand for high-precision micro-machining of these brittle materials to produce precision functional parts. Traditional ultra-precision micro-machining can lead to workpiece cracking, low machined surface quality, and reduced tool life. To reduce and further solve these problems, a new micro-machining process is needed. As one of the nontraditional machining processes, rotary ultrasonic machining is an effective method to reduce the issues generated by traditional machining processes of brittle materials. Therefore, rotary ultrasonic micro-machining (RUμM) is investigated to conduct the surface micro-machining of brittle materials. Due to the small diameter cutting tool (<500 μm) and high accuracy requirements, the impact of input parameters in the rotary ultrasonic surface micro-machining (RUSμM) process on tool deformation and cutting quality is extremely different from that in rotary ultrasonic surface machining (RUSM) with relatively large diameter cutting tool (∼10 mm). Up till now, there is still no investigation on the effects of ultrasonic vibration (UV) and input variables (such as tool rotation speed and depth of cut) on cutting force and machined surface quality in RUSμM of brittle materials. To fill this knowledge gap, rotary ultrasonic surface micro-machining of the silicon wafer (one of the most versatile brittle materials) was conducted in this study. The effects of ultrasonic vibration, tool rotation speed, and depth of cut on tool trajectory, material removal rate (MRR), cutting force, cutting surface quality, and residual stress were investigated. Results show that the ultrasonic vibration could reduce the cutting force, improve the cutting surface quality, and suppress the residual compressive stress, especially under conditions with high tool rotation speed. 相似文献
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The purified and acidified montmorillonite clay were characterized by XRD, BET and TPD. These results show that acidified clay is provided with more surface area and acid sites. For NH3-TPD, molecular NH3 desorption on purified clay and acidified clay occurs at temperatures with 873 and 1000 K, respectively. It is shown for the existence for strong acid sites. By two reactions of the tetrahydropyranylation of n-propanol and the esterification of cyclo-2-pentene with acetic acid, it is shown that the acidified clay displays better catalytic activity for above two organic reactions. By density-functional theory (DFT) method, we have analyzed the structures of different substituted montmorillonite and the effect sorption behavior of Na+ in different montmorillonite models. The result shows that the process of substitution will occur apart from octahedral aluminums. The adsorption of NH3 on clay surfaces have been investigated using TPD and DFT. This is shown that acid sites locate at round the octahedral aluminums, and substitution of Al3+ for tetrahedral Si will be favorable to NH3 adsorption. 相似文献
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《中国光学快报(英文版)》2016,(4)
The threshold of a laser-induced breakdown of air is determined experimentally and theoretically. We find that the ionization of air has two steps: the first step is a multi-photon ionization process, which provides enoughseed electrons to initiate the next step, and the second one is predominated by cascade ionization, which continues to produce free electrons geometrically until the critical free-electron density for breakdown is reached. So a two-step model based on the Morgan ionization model is established to describe the breakdown process. It is found that the time node dividing the two steps is about 9.8 ns in atmospheric air, and the threshold derived from the two-step model proposed here is more consistent with the experimental results than traditional ionization model. 相似文献
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Zehua Hong Xinwan Li Linjie Zhou Weiwen Zou Xiaomeng Sun Shuguang Li Jianguo Shen Haimei Luo Jianping Chen 《Optics Communications》2012,285(17):3592-3596
Novel highly-efficient power combiners based on evanescently-coupled micro/nano optical fibers are proposed and experimentally demonstrated. Experimental results show that the maximum power combing efficiency can be >90%. The combining efficiency is overlap length dependent. As long as the overlap length is long enough (~7 mm), a stable high combining efficiency can always be achieved. The presented optical power combiners with the advantages of easy fabrication, low-loss, low-cost, and wavelength insensitivity can find potential applications in micro/nano photonic devices, optical communications and optical interconnects. 相似文献
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The presented theoretical model for a mode-locked Nd-glass laser simultaneously takes into account dynamics of the mode-locking
dye, amplification saturation and radiation background. A systematic variation of laser parameters gives insight into the
pulse formation process and allows to improve the laser design. The calculations show that it should be possible to decrease
considerably the duration of light pulses of a mode-locked Nd-glass laser. Using a new mode-locking dye with a switching time
of τ=2.7×10−12 s we obtained stable laser operation and a pulse duration of 1.7×10−12s. 相似文献