运动无力场中的等离子体状况

<正> 在太阳活动区以及磁层和某些等离子体彗星中的磁场位形大多是无力场。无力场在太阳物理和空间物理中是常遇到的。我们经常通过无力场模型对客体进行理论分析和处理,然后与观测的结果进行比较。Gold和Hoyle最早提出太阳黑子磁场中的磁力线的扭绞特性。以后,人们用静力学的关系定量地计算了磁场与扭转过程的关系;开始是势场的磁场位形通

Internal resonance of an L-shaped beam with a limit stop .2. Forced vibration

A limit stop is placed at the elbow of an L-shaped beam whose linear natural frequencies are nearly commensurable. As a result of this hardening device the non-linear system exhibits multiple internal resonances, which involve various degree of coupling between the first five modes of the beam in free vibration. A point load is so placed as to excite several modes and the resulting forced vibration is examined. In the undamped case, three in-phase and two out-of-phase solution branches have been found. The resonance curve is extremely complicated, with multiple branches and interactions between the first four modes. The amplitudes of the higher harmonics are highly influenced by damping, the presence of which can effectively attenuate internal resonances. Consequently parts of the resonance curve may be eliminated, with the resulting response comprising different distinctive branches. (C) 1996 Academic Press Limited

球墨铸铁材料对激光的吸收率

球墨铸铁因其优良性能而被广泛用作模具材料。对球墨铸铁冲压模具的激光表面处理已成为改善其耐磨性、提高使用寿命的重要方法。一定激光参量下吸收率的大小又直接影响到表面处理的质量。因此，确定球墨铸铁材料对激光的吸收率十分必要。通过热电偶测温，计算机数据采集系统进行定点温度采集，并结合数值模拟方法，对吸收率进行了标定，即首先根据预置的吸收率计算，预测被测点处的温度响应，并与实测响应比较，不断修正吸收率值，使预测温度响应和实验值吻合，由此获得吸收率。采用这种方法获得了球墨铸铁材料在大气条件下对激光的吸收率为23．3％。为激光处理球墨铸铁材料时工艺参量的选择和优化提供了一定参考。

一类约束条件下的跟踪保性能控制

本文研究了一类时变非线性系统在输入有位置约束条件下的跟踪保性能控制问题．首先对非线性对象选择合适的特征运行状况，采用瞬时线性化技术得到多个线性化控制模型，将之看作是一个线性不确定系统，提出应用基于线性矩阵不等式的跟踪保性能控制设计控制器，然后经过推导得到了满足控制约束的充分条件，以定理的形式给出了约束条件下跟踪保性能控制器存在的充分条件．最后给出了仿真算例，仿真结果表明了所提方法的有效性和可行性．

Numerical Simulation of R-M Instability

In order to capture shock waves and contact discontinuities in the field and easy to program with parallel computation a new algorithm is developed to solve the N-S equations for simulation of R-M instability problems. The method with group velocity control is used to suppress numerical oscillations, and an adaptive non-uniform mesh is used to get fine resolution. Numerical results for cylindrical shock-cylindrical interface interaction with a shock Mach number Ms=1.2 and Atwood number A=0.818, 0.961, 0.980 (the interior density of the interface/outer density p(1)/p(2) = 10, 50, 100, respectively), and for the planar shock-spherical interface interaction with Ms=1.2 and p(1)/p(2) = 14.28are presented. The effect of Atwood number and multi-mode initial perturbation on the R-M instability are studied. Multi-collisions of the reflected shock with the interface is a main reason of nonlinear development of the interface instability and formation of the spike-bubble structures In simulation with double mode perturbation vortex merging and second instability are found. After second instability the small vortex structures near the interface produced. It is important factor for turbulent mixing.

Optical gain at 1550 nm from colloidal solution of Er3+-Yb3+ codoped NaYF4 nanocubes

We demonstrated optical amplification at 1550 nm with a carbon tetrachloride solution of Er3+-Yb3+ codoped NaYF4 nanocubes synthesized with solvo-thermal route. Upon excitation with a 980 nm laser diode, the nanocube solution exhibited strong near-infrared emission by the I-4(13/2) -> I-4(15/2) transition of Er3+ ions due to energy transfer from Yb3+ ions. We obtained the highest optical gain coefficient at 1550 nm of 0.58 cm(-1) for the solution with the pumping power of 200 mW. This colloidal solution might be a promising candidate as a liquid medium for optical amplifier and laser at the optical communication wavelength. (C) 2009 Optical Society of America

A scaling law of photoionization in few-cycle regime

In this paper, a scaling law of photoionization of atoms irradiated by intense, few- cycle laser pulses is established. The scaling law sets a relation to the phase- dependent ionization with the kinetic energy of photoelectrons, the duration and peak intensity of short pulses, and the ionization potential of the target atoms. We find that it will be advantageous to manifest the phase- dependent photoionization by choosing the target atoms with larger ionization potential, using laser with smaller carrier- frequency, and increasing the pulse intensity. (c) 2007 Optical Society of America.

反射型体全息光栅对超短脉冲激光光束衍射的性质

在光栅记录介质色散效应的影响下，拓展Kogelnik的耦合波理论研究了反射型体全息光栅对偏振方向垂直和平行于入射面的超短脉冲激光光束衍射的性质。结果表明对于记录在LiNbO3光折变晶体中的体全息光栅，在色散效应、光栅参量和入射条件的共同影响下，光栅对偏振方向垂直于入射面的超短脉冲激光光束衍射的光谱带宽大于对偏振方向平行于入射面的超短脉冲激光光束衍射的光谱带宽，在不考虑光栅介质色散效应的影响时，它们都变大。进一步给出了衍射光的光谱带宽及光栅的衍射效率随入射脉冲的光谱带宽与光栅的光谱带宽比值的变化情况。

基于套刻误差测试标记的彗差检测技术

为了满足光刻机投影物镜彗差测量精度的要求，提出一种基于套刻误差测试标记的彗差检测技术，分析了彗差对套刻误差测试标记空间像的影响，详细叙述了该技术的测量原理，并利用PROLITH光刻仿真软件对不同数值孔径与部分相干因子设置下套刻误差相对于彗差的灵敏度系数进行了仿真实验。结果表明，与目前国际上通常使用的投影物镜彗差检测技术相比，该技术在传统照明条件下灵敏度系数Kz7与Kz14的变化范围分别增加了27．5％和34．3％，而在环形照明条件下则分别增加了20．4％和22．1％，因此彗差的测量精度可提高20％以上。

一种新的长短光脉冲同步方案

单纵模长激光脉冲经分束后分别输入到两个波导调制器中，同时分别输入两个具有高同步准确度的电脉冲到调制器中．通过这种方式可以实现具有高同步准确度的长短光脉冲的输出．研究结果表明：该方案下长短脉冲的同步准确度可小于3．5ps（rms）．

Single mode Er-doped pi-phase-shifted distributed feedback fibre grating laser

A novel method incorporating the shielded method and the post-processing method has been proposed to fabricate the pi-phase-shilted fibre grating. Then an Er-doped pi-phase-shifted distributed feedback fibre grating laser has been fabricated using the grating. The laser threshold is 20 mW. When pumped with 90 mW light at 980 nm, the laser gives an output of 1.1 mW. Its signal-to-noise ratio is better than 60 dB. It is demonstrated that the laser is single mode operation by means of a Fabry-Perot scanning interferometer.

Stable single frequency and single polarization DFB fiber lasers operated at 1053 nm

Stable single-frequency and single-polarization distributed-feedback (DFB) fiber laser was realized by giving a pressure on the phase shift region of the fiber grating. The output wavelength of the DFB fiber laser is 1053 nm. When the pump power of 980 nm laser diode is 100 and 254 mW, the output power can reach 8.3 and 37.1 mW and the polarization extinction ratio was 26 and 20 dB, respectively. After chopped by Acousto-optic modulator (0.3 Hz), the pulse peak value variance is 4.65%(peak to peak) and 1.098% (RMS) for 31 min. (C) 2006 Elsevier Ltd. All rights reserved.

三维立体显示用稀土掺杂氧卤碲酸盐玻璃

制备了一种新的Er^3+／Tm^3+/Yb^3+共掺氧卤碲酸盐玻璃。研究了基质玻璃的热稳定性能、Raman光谱和上转换发光。发现：氧卤碲酸盐玻璃具有好的热稳定性能和低的声子能量，在980nmLD激发下，可同时观察到明显的蓝色(476nm)、绿色(530nm和545nm)和红色(656nm)上转换发光。上转换蓝光(476nm)是由于Tm^3+离子1^G4→3^3H6跃迁，上转换的绿光(530nm和545nm)是由于Er^3+离子2^H11/2→4^I15／2和4^S3/2→4^I15/2跃迁，上转换红光(6