Birefringence of Irregular-Microstructure Fibre

Birefringence of a microstructure fibre with irregular structures is investigated using the finite element method. The birefringence of each sample is statistically analysed, and the relation between the birefringence and the irregular structure of the microstructure fibre is derived. The results indicate that the irregular structure of the symmetrical microstructure fibre result in the birefringence which is more strongly affected by disorder of air holes than the nonuniformity. Moreover, lower birefringence can be obtained with smaller air holes and larger pitch in the fibre structure.     

裂纹或气泡对熔石英损伤修复坑场调制的近场模拟

建立了含有裂纹或气泡的高斯型修复坑的3维模型, 用3维时域有限差分方法研究了熔石英后表面该类缺陷对355 nm入射激光的近场调制. 研究表明, 裂纹的调制明显大于气泡或者高斯坑本身, 因此为了抑制修复元件的初始损伤, 应尽量避免任何未修复的裂纹存在, 尤其是与入射光呈夹角约25°的裂纹, 同时应避免尺寸大于5 λ 的气泡存在. 当裂纹或气泡位于近表面层3 λ 以内且靠近修复坑环边缘时, 对场的调制最明显. 随着侧移的增加, 近表面区缺陷诱导场叠加, 强点总数涨落较大且易形成极大峰值, 特别是含有裂纹的情形; 远表面区强点总数逐渐增大并趋于稳定. 随着嵌深的增加, 强点的数目大体呈减弱趋势, 当嵌深大于3 λ 时, 逐渐趋于平缓振荡. 如果裂纹或气泡位于坑点正下方几个波长内, 激光辐照下其效果相当于延长了高斯坑的深度.     

加工误差引入的薄型KDP晶体附加面形

针对惯性约束聚变（ICF）驱动装置中口径为400 mm400 mm薄型频率转换KDP晶体在45放置状态下产生的附加面形问题,采用有限元分析软件ANSYS,建立了以实测数据为基础的大口径薄型KDP晶体的应变模型和有加工误差的夹具模型,仿真分析了KDP晶体的加工误差和夹具的加工误差对KDP晶体附加面形的影响, 给出了KDP晶体附加面形变化的P-V值和RMS值。在此基础上,通过对KDP晶体的加工误差及夹具支撑表面不同类型和不同大小加工误差的分析和比较,得出:KDP晶体边缘的加工误差和夹具支撑表面的凹型加工误差是引起较大附加面形的原因之一,KDP晶体的加工误差也会导致其面形变化不均匀,而夹具支撑表面的凸型、波浪形加工误差和压条表面的随机加工误差对KDP晶体附加面形的影响相对较小,且支撑表面的随机加工误差引起的附加面形变化介于其他两者之间。     

透红外含碲氟铝基玻璃的激光损伤阈值

 在氟铝酸盐玻璃组分中加入适量声子能量低的重金属氧化物TeO ₂，得到一种新的氧氟化物玻璃。该材料具有良好的成玻璃性能，适合制作大尺寸红外窗口镜。研究了TeO2含量对玻璃特征温度、阿贝数和红外透过性能的影响。同时测试了这种玻璃的抗DF激光能力，结果表明： TeO ₂含量为15%的玻璃，DF激光破坏阈值达14.95 kＷ·cm^-2。分析显示，由于玻璃基质的多声子吸收，对激光能量的吸收而引起的热冲击是导致玻璃破坏的主要原因。进一步降低玻璃中水分，可以提高玻璃抗激光破坏性能。     

Wavelet--fractional Fourier transforms

This paper extends the definition of fractional Fourier transform (FRFT) proposed by Namias V by using other orthonormal bases for $L^{2}\left( R \right)$ instead of Hermite--Gaussian functions. The new orthonormal basis is gained indirectly from multiresolution analysis and orthonormal wavelets. The so defined FRFT is called wavelets-fractional Fourier transform.     

PET与SAN/PAN复合膜界面的 FTIR-ATR研究

应用傅里叶衰减全反射红外光谱(FTIR-ATR)技术对聚对苯二甲酸乙二酯(PET)表面形成不同厚度的超薄苯乙烯-丙烯腈共聚物(SAN)和聚丙烯腈(PAN)的共混物膜及其SAN/PAN共混物膜的厚度、界面层PET亚甲基的构像变化等进行研究,结果表明PET表面共混物膜的厚度随共混物混合液中SAN含量的增加而增加,界面层成膜物质与基材的分子链段间发生了相互渗透和扩散,分子链的极性越相近,越容易成膜.对PET红外光谱吸收峰的A1340/A1410进行定量研究表明,在成膜过程中,PET分子链的亚甲基构像由反式向旁式转变,引起界面层PET的结晶度降低.FTIR-ATR是分析复合膜界面层结构信息的有效方法.     

非共线和频过程中的表面散射杂散光分析

以三次谐波自相关测量原理为出发点,研究了其和频过程中BBO晶体的表面散射杂散光。详细推导了由晶体表面散射引入的杂散光的具体表达式,定量分析了其对和频过程中输出信号的对比度的影响。分析表明,杂散光强度与晶体表面粗糙度有一定的关系。晶体表面粗糙度为激光波长的1%时,引入的杂散光噪声约为10-8。表面越光滑,引入的噪声越小。     

基于本征正交分解的串列叶栅多目标气动优化研究

为提高压气机串列叶栅复杂气动构型优化设计的效率,本文基于本征正交分解(POD)理论,建立了集几何外形参数化、样本空间降维、气动性能求解、降维模型构建和遗传算法寻优于一体的串列叶栅高效优化设计系统,针对叶型型面和叶片相对位置关系参数,开展了多目标优化设计工作。在7°攻角工况下,优化后的串列叶栅的静压升提高了0.53%,总压损失系数下降了9.25%,其他攻角条件下叶栅性能同样也得到了改善。与传统CFD方法相比,极大提高了优化效率,与基于Kriging代理模型相比,本文发展的优化系统由于缩小了设计变量空间,提高了优化的迭代效率,收敛耗时仅为Kriging代理模型的0.0796%。此外,基于POD方法的优化设计系统具有更高的建模精度,使串列叶栅获得了更高的静压升和更低的总压损失系数。优化后的串列叶栅节距系数增大、弯角比减小,减小了掺混损失,抑制了流动分离,改善了全攻角范围内的气动性能。     

High-order harmonic generation spectrum of an excited one-dimensional Coulomb atom in an intense laser field

Response of the wave packet of a one-dimensional Coulomb atom to an intense laser field is calculated using the symmetrized split operator fast Fourier method. The high-order harmonic generation (HHG) of the initial state separately being the ground and excited states is presented. When the hardness parameter \alpha in the soft Coulomb potential V(x)=-1/\sqrt{x^2+\alpha} is chosen to be small enough, the so-called hard Coulomb potential V(x)=-1/|x| can be obtained. It is well known that the hard one-dimensional Coulomb atom has an unstable ground state with an energy eigenvalue of $\sim0.5$ and it has no states corresponding to physical states in the true atoms, and has the first and second excited states being degenerate. The parity effects on the HHG can be seen from the first and second excited states of the hard one-dimensional Coulomb atom. The HHG spectra of the excited states from both the soft and hard Coulomb atom models are shown to have more complex structures and to be much stronger than the corresponding HHG spectrum of the ground state of the soft Coulomb model with $\alpha=2$ in the same laser field. Laser-induced non-resonant one-photon emission is also observed.