（3＋1）-dimensional nonlinear propagation equation for ultrashort pulsed beam in left-handed material

In this paper a comprehensive framework for treating the nonlinear propagation of ultrashort pulse in metamaterial with dispersive dielectric susceptibility and magnetic permeability is presented. Under the slowly-evolving-wave approximation, a generalized （3＋1）-dimensional wave equation first order in the propagation coordinate and suitable for both right-handed material （I~HM） and left-handed material （LHM） is derived. By the commonly used Drude dispersive model for LHM, a （3＋1）-dimensional nonlinear Schrodinger equation describing ultrashort pulsed beam propagation in LHM is obtained, and its difference from that for conventional RHM is discussed. Particularly, the self-steeping effect of ultrashort pulse is found to be anomalous in LHM.     

超短脉冲激光空间调制下小尺度自聚焦的实验研究

实验研究了超短脉冲激光的空间小尺度自聚焦的动态变化过程.具体实验过程是使经过正交细丝的衍射来实现激光的空间调制,然后通过非线性Kerr介质二硫化碳,随着输入功率的增大,超短脉冲开始出现小尺度自聚焦增长现象.实验发现,每个小尺度自聚焦峰值并不是随着功率的增大而无限地增长下去,而是在不同位置出现了新的调制增长点,这些新出现的增长与原有的增长相互竞争,最终导致了分裂成丝.通过数值模拟相应的传输过程,发现数值模拟结果与实验结果符合很好. 关键词： 小尺度自聚焦 高功率激光 超短脉冲     

FILAMENTATION INSTABILITY OF LASER BEAMS IN NONLOCAL NONLINEAR MEDIA

The filamentation instability of laser beams propagating in nonlocal nonlinear media is investigated. It is shown that the filamentation instability can occur in weakly nonlocal self-focusing media for any degree of nonlocality, and in defocusing media for the input light intensity exceeding a threshold related to the degree of nonlocality. A linear stability analysis is used to predict the initial growth rate of the instability. It is found that the nonlocality tends to suppress filamentation instability in self-focusing media and to stimulate filamentation instability in self-defocusing media. Numerical simulations confirm the results of the linear stability analysis and disclose a recurrence phenomenon in nonlocal self-focusing media analogous to the Fermi-Pasta-Ulam problem.     

高功率激光放大器中光束的成丝和B积分

研究了高功率激光放大器中光束的成丝问题,利用弗兰兹－诺德威克（Frantz-Nodvik)模型将准稳态波动议程推广到介质有饱和增益的情形,进而得到高功率激光放大器中小尺度调制的传输方程,在小信号增益和饱和增益情形下,分别得到了小尺度调制方程的精确解析解和数值解。结果表明,对于相同的输入光强,增益使小尺度调制增益谱的范围加宽,最快增长频率增高,最大增长率提高;同时,在放大介质中,小尺度调制的最快增长频率和最大增长率还随传输距离变化,增益饱和效应使小尺度调制的增长速度以及B积分的增长低于无饱和放大情形。     

梯度折射率介质中高斯光束的非线性传输特性

 利用无像差自聚焦理论研究了梯度折射率非线性Kerr介质中高斯光束的传输特性,得到了高斯光束光斑半径和波面曲率半径的表达式。解析结果清楚地表明了衍射、自聚焦以及梯度折射率效应之间的竞争对高斯光束传输行为的影响。梯度折射率效应使光束自聚焦的距离缩短。     

超常介质中超短电磁脉冲的传输特性研究

将超常介质的色散磁导率合并到非线性极化项中,借鉴常规介质中超短脉冲传输方程的推导方法,得到了非线性超常介质中超短脉冲的传输方程。在德鲁德(Drude)色散模型下,根据脉冲中心频率的不同在传输方程中出现了可正、可负、可为零的自陡峭系数,以及高阶非线性色散项。此外,利用矩方法对传输方程进行分析,得到了超常介质中超短脉冲传输方程的能量守恒定律表达式,揭示了色散磁导率导致的超短脉冲传输的新特性,发现二阶非线性色散使超短脉冲的能量、脉冲频移、脉冲宽度、中心位置和啁啾都随传输距离呈现振荡式变化。     

Nonlinear images of scatterers in chirped pulsed laser beams

The bandwidth and the duration of incident pulsed beam are proved to play important roles in modifying the nonlinear image of amplitude-type scatterer.It is found that the initially positive chirp-type bandwidth can suppress the nonlinear image,while the negative one can enhance it,and that both effects are inversely proportional to the incident pulse duration.Numerical simulations further demonstrate that the location of nonlinear image is at the conjugate plane of the scatterer and that,for negatively pre-chirped pulsed beam,the nonlinear image peak intensity can be higher than that in the corresponding monochromatic case under certain conditions.Moreover the effect of group velocity dispersion on nonlinear image is found to be similar to that of chirp-type bandwidth.     

各向异性超常材料平板透镜的聚焦特性分析

运用矢量角谱理论研究各向异性超常材料平板透镜的聚焦特性,得到了光束在平板透镜内外各区域的矢量场分布,揭示了超常材料平板透镜的聚焦特性跟材料的各向异性参数之间的定量关系,发现聚焦场的偏振态因平板透镜的各向异性特性而发生改变.作为矢量理论的具体应用,分析了光轴方向磁导率为-1,其他各向异性参数均为1的超常材料平板透镜的聚焦特性,发现此类透镜对初始沿某一横向方向偏振的光束能实现部分聚焦,并发生偏振旋转现象.     

SO_4~(-2)/Fe_2O_3-Al_2O_3纳米固体酸的红外光谱研究

用 IR光谱研究了 SO2 -4 / Fe2 O3- Al2 O3纳米固体酸在不同焙烧温度下表面结构与酸性的变化 ,结果表明 ,当焙烧温度在 4 5 0— 5 0 0℃时 ,双齿螯合配位结构特征谱带齐全 ,酸性强 ,小于 4 5 0℃时 ,双齿螯合配位特征谱带不齐全 ,酸性不强 ,而大于 5 0 0℃时 ,随着温度的升高 ,特征谱带区域宽化 ,特征峰消失 ,酸性变弱。此外 ,从 Fe- O纳米颗粒的特征振动带显示可得知 ,样品的粒径小于 30 nm。     

六～八元瓜环与咪唑[4,5-f]-1'''',10''''-菲咯啉衍生物的相互作用

合成了2-苯基-咪唑[4,5-f]-1',10'-菲咯啉和对二甲氨基-2-苯基-咪唑[4,5-f]-1',10'-菲咯啉两种咪唑[4,5-f]-1',10'-菲咯啉衍生物,并经过一、二维核磁共振谱以及质谱方法的验证.利用1H NMR、质谱以及紫外可见分光光度法,考察了以六～八元瓜环为主体,咪唑[4,5-f]-1',10'-菲咯啉衍生物为客体的作用体系,以及形成的主客体包结配合物的结构特征.研究结果表明三种瓜环均与2-苯基-咪唑[4,5-f]-1',10'-菲咯啉发生相互作用,客体以较小的苯基一端穿过瓜环内腔直至苯基部分和菲咯啉部分分别露置在瓜环的两个端口外,特别是八元瓜环能容纳两个客体分子.而对二甲氨基-2-苯基-咪唑[4,5-f]-1',10'-菲咯啉仅能与七及八元瓜环相互作用,作用模式与前者相同.