We demonstrate that the directionality of far-field second harmonic (SH) emission generated from individual gold nanosphere can be flexibly engineered by manipulating three-dimensional (3D) focal polarization orientation of the excitation field, which is explained by the coherent interference between SH dipolar and quadrupolar emission modes. The SH dipolar emission mode is independent of the polarization direction of the fundamental field whereas the evolution of the focal polarization orientation can dramatically modify the quadrupolar emission pattern. Therefore, the resultant SH emission pattern has a polarization-dependent behavior and side scattering almost perpendicular to the propagation direction of the incident light can be observed under a specific condition. Our findings provide a novel degree of freedom for all-optical control of directional nonlinear scattering from single nanoantenna, thereby opening new possibilities for future potential applications.

A method for improving lateral resolution and reducing imaging distortion of optical subtraction microscopy is pro-posed. First, an azimuthally polarized (AP) light is modulated by an annular aperture. Then, an image with higher lat-eral resolution is obtained by subtracting an image obtained by an annular AP beam from an image obtained by a ra-dially polarized beam. The simulation results demonstrate that compared with the case without the annular aperture, negative side-lobes in the effective point spread function are effectively suppressed, and the imaging quality of sub-traction microscopy is obviously enhanced.

An electromagnetically induced transparency (EIT) in metamaterial resonator with two bright modes and one dark mode at the terahertz (THz) band is numerically and experimentally demonstrated. Different from two kinds of the traditional passive modulations, our design can realize the passive modulation of EIT phenomenon by adding another bright mode resonator. Simulated and experimental results show that the transmission peak varies for incident THz waves with different polarization directions due to its asymmetric structure, which provides a novel way to realize high efficiency switch and modulation.

Based on the generalized Mie theory, refractive index sensing characteristics of single silver nanoparticle respectively illuminated by tightly focused linearly-polarized and radially-polarized light beams are investigated. The spectra for localized surface plasmon resonances (LSPR) under different dielectric environments demonstrate that distinct dipolar and quadrupolar resonances can be always observed for the case of radial polarization, while there is only strong dipolar resonance for the case of linear polarization. The dipolar mode has a higher sensitivity. However, the figure of merit (FOM) for the quadrupolar resonance is much higher than that for the dipolar resonance, because the quadrupolar resonance has a narrower width.

蛋白质结构失稳后会发生错误折叠、 集聚或纤维化, 不仅丧失正常功能, 有时甚至会产生生物毒性, 导致相关疾病。 纤维化了的蛋白质是神经退行性疾病以及二型糖尿病等的主要诱因, 它在溶液中具有和淀粉类似的特性, 因此蛋白质的纤维化又被称为淀粉样变性。 电磁辐射是引起蛋白质结构失稳的一个常见因素。 经电场辐照后, 蛋白质会发生去折叠和集聚, 改变自发折叠机制。 同时, 经受电场辐照的扰动而失稳的蛋白质, 纤维化过程也会受到一定的影响。 以胰岛素为研究对象, 利用硫磺素T(ThT)染色的荧光光谱法、 透射电子显微镜(TEM)以及圆二色谱(CD)法, 分别从纤维化的宏观动力学过程、 成熟纤维丝微观形貌以及原纤维二级结构组成等不同角度, 探究经33 Hz脉冲电场(PEF)不同电场强度及不同持续时间辐照后蛋白质在体外淀粉样变性机制的变化情况。 结果表明, 胰岛素溶液经过33 Hz PEF辐照后, 淀粉样变性初期产生前体蛋白的成核期延长, 原纤维丝聚集延长过程(即中间产物的寿命)缩短, 形成的成熟纤维丝长度变短且整齐成簇无分支。 这些效应随着辐照电场强度和辐照时间的增加而有不同程度的加强。 研究结果一致说明PEF辐照对胰岛素的淀粉样变性有一定的抑制作用。

A terahertz bandpass filter with the sandwich structure consisting of thermally tunable vanadium dioxide (VO₂) thin film, silica substrate and subwavelength rectangular Cu hole arrays is designed and theoretically analyzed. The results show that the transmittance of the filter can be actively tuned by controlling the temperature of VO₂, the narrow band terahertz (THz) waves with the transmittance from 85.2% to 10.5% can be well selected at the frequency of 1.25 THz when the temperature changes from 50 ℃ to 80 ℃, and the maximum modulation depth of this terahertz bandpass filter can achieve 74.7%.

Using the vector diffraction theory and the phenomenological model, this paper investigates the second harmonic generation (SHG) of a single centrosymmetric nanosphere excited by focused doughnut beams (DBs) with different topological charges. The results show that strong backward SHG (BSHG) appears when the particle is excited by focused DBs with topological charges of ±1. The backward second harmonic radiation can be caused by the depolarized effect of high numerical aperture (NA) objectives due to the strong longitudinal components.

将视觉注意机制引入到直方图构造中,并在此基础上提出了一种新的基于灰度级信息量直方图的图像增强算法.该算法利用Itti视觉注意计算模型对图像的显著性进行分析,获得全局显著图；然后,将全局显著图划分为若干等大的子区域,求取各子区域的平均显著值,并做归一化处理,得到子区域的加权统计系数；再将各子区域的灰度级加权统计值相加,得到灰度级信息量直方图；最后,依据直方图均衡化的映射函数,调整灰度级的动态范围.实验结果表明,该算法明显优于经典的GHE算法和AHE算法,具有满意的视觉效果.