激光诱导Ni等离子体特性的研究

以Nd·YAG激光器的二倍频输出作为激发源,获得了激光诱导Ni等离子体的发射光谱,基于发射光谱,对等离子体电子激发温度和电子密度进行了测量,其典型值分别为3 714 K,4.67×1016 cm-3。测量了等离子体电子激发温度和电子密度的空间分布,发现沿垂直于激光传播方向的径向,随到中心点距离的增加,等离子体辐射的强度减小,但线型和线宽不变,表明等离子体电子激发温度和电子密度沿径向均匀分布。沿激光传播方向,随到样品表面距离的增加,等离子体辐射强度、电子激发温度和电子密度先增加后降低,在距样品表面1.5 mm处,达到最大值。采用激光诱导击穿光谱技术进行相关探测时,收集距离样品表面1.5 mm处的发射谱,有利于提高探测灵敏度。     

Viewing angle characteristics of a nematic liquid crystal cell with two crossed-grating surface substrates

Liquid crystal in a nematic liquid crystal cell surface with two crossed-grating surface substrates can be oriented along the normal grating direction with given geometric parameters of groove and anchoring strength. This display is equivalent to multi-domain vertical-alignment mode. It has a relatively wide viewing angle. In this letter, we investigate the viewing angle characteristics of this kind of cell. The viewing angle dependence of contrast ratio is obtained using the extended Jones matrix method, which also considers the flexoelectric effect. The viewing angle is dependent on the geometric parameter of grating surface, the flexoelectric coefficients, and the anchoring strength. Therefore, appropriate value for each factor needs to be selected to obtain a better viewing angle of this cell.     

双螺旋凹槽结构超表面检测偏振状态的研究

偏振态信息与轨道角动量信息是光学信息的重要载体,也是光学信息处理的重要参量,在石英基底上设计了阿基米德双螺旋结构,利用有限元法计算了带有不同轨道角动量和偏振态信息的入射光照射到上述超构表面时,入射光与超表面耦合所产生的透射光呈现不同强度分布的图样,根据该图样,可检测入射光的偏振态信息.为检测入射光的轨道角动量,还提出了...     

Control of the patterns by using time-delayed feedback near the codimension-three Turing–Hopf–Wave bifurcations

Control of the spatiotemporal patterns near the codimension-three Turing–Hopf–Wave bifurcations is studied by using time-delayed feedback in a three-variable Brusselator model. Linear stability analysis of the system shows that the competition among the Turing-, Hopf- and Wave-modes, the wavenumber, and the oscillation frequency of patterns can be controlled by changing the feedback parameters. The role of the feedback intensity Pu played on controlling the pattern competition is equivalent to that of Pw, but opposite to that of Pv. The role of the feedback intensity Pu played on controlling the wavenumber and oscillation frequency of patterns is equivalent to that of Pv, but opposite to that of Pw. When the intensities of feedback are applied equally, changing the delayed time could not alter the competition among these modes, however, it can control the oscillation frequency of patterns. The analytical results are verified by two-dimensional （2D） numerical simulations.     

Doping Defects in Two-Dimensional Holographic Photonic Crystals Using a Continuous-Wave Visible Laser

It is demonstrated that defects of any shape or size can be doped in holographic photonic crystals using a cw visible laser and spherical/cylindrical lens. Defects with different sizes at any depth in the material can be obtained by controlling the position of the foca/point of the lens and exposure value. We facilitate the implementation of sub-wavelength arbitrary point or line defects in large-size 2D holographic photonic crystals.     

非线性曝光对三维全息光子晶体禁带特性的影响

从理论和实验两方面研究了非线性曝光对全息方法制作光子晶体的影响.使用低折射率材料（n=152）制作了金刚石结构光子晶体,通过控制曝光量使记录介质工作在非线性曝光区域,发现光子禁带的特性得到了明显的改善.并由此提出了用低折射率材料实现全空间禁带的设想. 关键词： 光子晶体 光学全息 非线性曝光