小孔矩形腔体屏蔽特性的研究

本文提出了有孔腔体远、近场电磁屏蔽效能的计算方法，体研究了矩形腔体的屏蔽特性，讨论了各类孔对屏蔽能的影响程度。数值结果表明，理论计算与实验数据吻合较好。     

介质加载圆柱腔的场分析

本文应用严格场匹配法解决了介质加载圆柱腔的本征问题，计算了圆柱腔在纵向部分填充介质后ＴＥ０１ｎ模和ＴＭ０１ｎ模的本征频率和本征场型的变化。特别分析了本征模式在空气段为截止模的情况。本文的分析方法亦可应用到纵向部分填充介质的传输线和其它形状的谐振腔。     

高功率板条固体激光器研究的进展

本文对高功率板条固体激光器研究的进展和应用前景作了综合评述。结合作者部分工作,对板条激光器的热效应、聚光器和光学谐振腔等关键问题和技术进行了物理分析。     

Coupling Losses for Resonators with Unequal Apertures for Extended Fresnel Numbers

Coupling losses have been calculated for laser resonators with unequal apertures and extended Fresnel Numbers. This was done using both, diffraction theory and a simple linear model.A close form expression was derived to calculate coupling losses with reasonable accuracies for a limited range of paramters. This should help in the preliminary design of hole coupling laser resonators.     

超Jaynes-Cummings模型中的原子置于热辐射场时的相干特性

超Jaynes一Cummings模型中的两能级原子置于热辐射场。通过求解原子与热辐射场相互作用过程中原子约化密度算符非对角元．精确得出子原子相干性的衰变规律。研究了在相互作用系统中外加驱动场时可保持原子的相干性，此时外加驱动场的时间演化与原子的跃迁频率、原子偶极矩、热库的温度和k模光子频率等因素有关。     

北京自由电子激光最近进展──实现饱和振荡

北京自由电子激光(BFEL)装置于1993年底在10.68μm处实现了饱和振荡.输出激光能量为3mJ,饱和平顶宽度2μs.对应饱和振荡平均功率为210kW(宏脉冲),峰值功率约为20MW,比自发辐射高8个量级,单程小讯号净增益为24%,转换效率为0.45%,与理论预期结果相符.光束质量接近衍射极限.目前装置可工作于9-11μm.     

自成像列阵共振腔的分析——Ⅰ.Talbot共振腔

利用自成像效应进行半导体列阵激光器锁相是一种重要的外腔锁相技术,所构成的共振腔可分为Talbot腔和带相位补偿板的Lau腔。我们用Fox-Li方法计算了共振模式。本文给出了Talbot腔的计算结果和分析,表明同相和反相模的损耗随腔长变化存在临界点。     

一种新型谐振腔增强型光调制器结构的研究

提出了一种新型谐振腔增强型(RCE)光调制器结构,它由一个对称型谐振腔增强型光调制器和一个高反镜所构成.利用传输矩阵法对该器件的插入损耗及临界吸收厚度进行了模拟分析,并同传统谐振腔增强型光调制器的相关性能进行了比较.分析结果表明,这种结构解决了传统谐振腔增强型光调制器的临界吸收厚度与插入损耗之间相互制约的矛盾,可同时获得低临界吸收厚度和低插入损耗.     

Transient free‐surface flow of a viscoelastic fluid in a narrow channel

The interplay between inertia and elasticity is examined for transient free‐surface flow inside a narrow channel. The lubrication theory is extended for the flow of viscoelastic fluids of the Oldroyd‐B type (consisting of a Newtonian solvent and a polymeric solute). While the general formulation accounts for non‐linearities stemming from inertia effects in the momentum conservation equation, and the upper‐convected terms in the constitutive equation, only the front movement contributes to non‐linear coupling for a flow inside a straight channel. In this case, it is possible to implement a spectral representation in the depthwise direction for the velocity and stress. The evolution of the flow field is obtained locally, but the front movement is captured only in the mean sense. The influence of inertia, elasticity and viscosity ratio is examined for pressure‐induced flow. The front appears to progress monotonically with time. However, the velocity and stress exhibit typically a strong overshoot upon inception, accompanied by a plug‐flow behaviour in the channel core. The flow intensity eventually diminishes with time, tending asymptotically to Poiseuille conditions. For highly elastic liquids the front movement becomes oscillatory, experiencing strong deceleration periodically. A multiple‐scale solution is obtained for fluids with no inertia and small elasticity. Comparison with the exact (numerical) solution indicates a wide range of validity for the analytical result. Copyright © 2004 John Wiley & Sons, Ltd.