色散对高能激光光纤前端FM-AM效应的影响

<正>弦相位调制脉冲可以满足高能激光驱动器对宽带和束匀滑的要求,在光纤系统中传输后,由于光纤中群速度色散的作用,将会产生强度调制,从而加剧光纤功率放大器中的非线性效应和光谱整形的难度.通过对2GHz,14·25GHz正弦相位调制脉冲经过不同光纤长度传输实验为例,结合光纤系统中色散对FM-AM效应影响的理论分析,发现2GHz相位调制脉冲的实验结果与模拟结果符合较好.     

基于光纤自相位调制多波长全光再生的色散管理优化

针对基于光纤自相位调制效应的多波长全光再生系统,分析了光纤平均色散对再生器品质因子改进量的影响,提出一种色散管理优化方法.由于波长间色散差异会导致再生系统性能的稳定性下降,通过选择色散补偿光纤和单模光纤的长度,使其合成的色散曲线与各波长分别达到最优再生性能时对应的色散曲线近似拟合,同时保证该色散曲线落在性能满意度高的色散区域,然后调整信号输入功率和滤波器的偏移量,可有效改善多波长再生性能的稳定性,实现再生器的色散管理优化.     

介质不均匀性对激光模式相位与光强分布的影响

将不均匀介质势函数进行泰勒展开,取其前3项近似,与描述光腔模式的亥姆霍兹方程中的特殊函数结合,根据光腔边界条件推导出光腔模式的本征解、激光输出功率以及不均匀介质与激光模式的相位与强度分布关系表达式。将表达式应用于氧碘化学激光器的功率与输出耦合率的非线性拟合以及近场光强分布的分析,预测趋势与文献结果相符。     

轴对称-折叠组合腔CO_2激光器原理性实验研究(英文)

报道了轴对称-折叠组合腔CO2激光器原理性实验研究,激光器能在CW模式下成功运行。研究得到了激光器最佳的气体比率和气体压强。通过研究CO2激光器的不同方面,如激励门电压和输出功率等,发现它们随着放电电流的变化而变化。通过实验得到了激光光束的光斑和聚焦的实验光斑,并模拟了光强分布。激光器已经成功的组建、运行和调试,获得的最大输出功率为58 W。     

S波段低温低噪声放大器的研制

介绍了基于ADS仿真的低噪声放大器的设计与制作方法;重点研究了LNA的直流偏置、稳定性分析、匹配设计、版图制作和调试;提出了源级负反馈和栅极加并联阻抗的方法来实现了电路全频段稳定和低温正常工作。采用ATF-34143制作了中心频率在2.25的低噪声放大器,在77K温度下,该放大器带内输入输出驻波比小于1.2,增益达到23dB,噪声系数为0.24dB。     

高功率980nm垂直腔面发射激光器的亮度特性

在循环水冷却(工作环境温度控制在15℃)和连续注入电流条件下,从垂直腔面发射激光器(VCSEL)亮度基本定义出发,实验测量了不同注入电流时口径为400μm的高功率980nm InGaAs/GaAs应变量子阱垂直腔面发射激光器(VCSEL)的亮度特性。结果表明:在注入电流4 A时,随着注入电流的增加,亮度也跟着增加;当注入电流4A时,尽管输出功率在增加,但是器件的光束质量变差,M2因子升高,表明此时影响器件亮度的主导因素是M2因子,所以亮度减小;在注入电流为4A,输出功率为1.2W时,亮度达到最大值2.43kW/cm2.sr,此时的光束质量最好,M2因子为207。最后,分析了影响高功率VCSEL器件亮度特性的主要因素,提出了提高器件亮度特性的解决方法。     

An analysis of seismic attenuation in random porous media

The attenuation of seismic wave in rocks has been one of the interesting research topics, but till now no poroelasticity models can thoroughly explain the strong attenuation of wave in rocks. In this paper, a random porous medium model is designed to study the law of wave propagation in complex rocks based on the theory of Biot poroelasticity and the general theory of stochastic process. This model sets the density of grain, porosity, permeability and modulus of frame as random parameters in space, and only one fluid infiltrates in rocks for the sake of better simulation effect in line with real rocks in earth strata. Numerical simulations are implemented. Two different inverse quality factors of fast P-wave are obtained by different methods to assess attenuation through records of virtual detectors in wave field (One is amplitude decay method in time domain and the other is spectral ratio method in frequency domain). Comparing the attenuation results of random porous medium with those of homogeneous porous medium, we conclude that the attenuation of seismic wave of homogeneous porous medium is far weaker than that of random porous medium. In random porous media, the higher heterogeneous level is, the stronger the attenuation becomes, and when heterogeneity σ = 0.15 in simulation, the attenuation result is consistent with that by actual observation. Since the central frequency (50 Hz) of source in numerical simulation is in earthquake band, the numerical results prove that heterogeneous porous structure is one of the important factors causing strong attenuation in real stratum at intermediate and low frequency.     

一种岩石断裂韧度试样应力强度因子的三维边界元法标定

用三维边界元法(BEM)标定了一种岩石断裂韧度试样的柔度,求出了这种试样的平均无量纲应力强度因子(SIF),并得到了对应于最大载荷时的临界裂纹长度和平均无量纲SIF的最小值.     

BABAR measurement of baryon time-like form factors via initial state radiation

BABAR has measured with unprecedented accuracy the e^＋e^- → pp and e^＋e^- →∧∧ cross sections by means of the initial state radiation technique, which has the advantages of good efficiency, good energy resolution and full angular acceptance, even exactly at threshold. A peculiar feature of these cross sections is their non-vanishing values at threshold. In the case of charged baryons, this phenomenon is expected according to the Coulomb interaction between the outgoing baryon and antibaryon. Once this Coulomb enhancement factor is taken into account, the striking result is achieved that the proton form factor at threshold is ｜GP（4Mp^2）｜ = 1, that is what is expected for pointlike fermion pairs, in spite of the proton structure. However a Coulomb enhancement factor is not expected for neutral fermions, likely in contradiction with the BABAR data. Qualitatively this behaviour is consistent with Coulomb interactions at the valence quark level.     

Space- and time-like electromagnetic pion form factors in light-cone pQCD

We present a combined analysis of the space- and time-like electromagnetic pion form factors in light-cone perturbative QCD with transverse momentum dependence and Sudakov suppression. Including the genuine non-perturbative “soft” QCD and the power suppressed twist-3 corrections to the standard twist-2 perturbative QCD result, the experimental form factor data available at moderate energies/momentum transfers can be explained reasonably well. To this end, the bulk of the existing discrepancy between the space- and time-like experimental data is ostensibly reconciled.