Scattering and Focusing Effect of Stepped Index Luneberg Lens

Focusing effect of the Luneberg lens for wide bandwidth is studied with emphasis on experiment. A model experiment was performed using a stepped index (six-layer) spherical lens. The total electric field amplitude along the propagation axis has the maximum value (focal point) on the surface of the lens. As the size parameter ka (k: wave number, a: radius of the sphere) is larger, the electric field amplitude at the focal point becomes larger. These results correspond with the power of convergence (focusing effect) by the Luneberg lens. The experimental values are in a good agreement with theoretical ones that are calculated using homogeneous multilayered approximate method. They are also in a good agreement with the results using exact solutions for the inhomogeneous dielectric sphere (the ideal Luneberg lens). Therefore, it is found that the six-layer spherical lens has the optimum variation of dielectric constants for the Luneberg lens and maintains focusing effect for wide bandwidth.     

Electric field-driven structural changes in cholesteric shells for optical applications

Cholesteric liquid crystal (CLC) shells with planar anchoring condition were prepared by using a capillary microfluidic technology. Under the influence of an electric field, shells were studied by filling them in glass cells coated with transparent ITO working as an electrode. CLC shells with a planar texture having dark brushes at 0 V under crossed polarizers transformed into a focal conic domain, a fingerprint texture, and finally to an isotropic phase with an increase of electric field that was confirmed by inserting the Bertrand lens in the polarized light path. In addition, our studies also show that the electric-field-driven isotropic phase was due to dielectric heating and local heating effects. The calculated magnitude of the local heating result from the model was in agreement with the experimental observation together with the chiral nematic to isotropic transition due to conventional heating.     

A lens formula for an electrostatic lens accompaning pre- and after electric fields

The virtual object and image are introduced in order to apply the usual lens formula to an electrostatic lense accompaning pre- and/or electric fields. In case of the uniform electric field, their positions are simply expressed as a function of the accelerating or decelerating potential ratio.     

Spectral and Lensing Characteristics of Gel-Derived Strontium Tartrate Single Crystals Using Dual-Beam Thermal Lens Technique

The Dual Beam mode-matched thermal lens spectrometry is a sensible technique for direct measurements of the thermal properties of tartrate crystalline materials. Here we report the measurement of thermal diffusivity of Strontium Tartrate single crystals incorporated with Rhodamine 6G using the thermal lens experiment. The respective crystals were prepared by solution-gel method at room temperature. The absorption characteristics of three different Strontium Tartrate crystals viz. pure, electric field applied and magnetic field applied were also carried out.     

Dynamics of a dielectric droplet suspended in a magnetic fluid in electric and magnetic fields

The behavior of a microdrop of dielectric liquid suspended in a magnetic fluid and exposed to the action of electric and magnetic fields is studied experimentally. With increasing electric field, the deformation of droplets into oblate ellipsoid, toroid and curved toroid was observed. At the further increase in the electric field, the bursting of droplets was also revealed. The electrorotation of deformed droplets was observed and investigated. The influence of an additional magnetic field on the droplet dynamics was studied. The main features of the droplet dynamics were interpreted and theoretically examined.     

折射率渐变透镜的数值设计

传统折射率渐变透镜的设计要求初级馈源天线具有稳定的相位中心,这就限制了透镜的应用范围。为拓宽透镜的应用范围,提出了一种折射率渐变透镜的数值设计方法,通过对馈源天线的极化电场离散采样获得相位信息,并据此设计透镜,随后用金属短线结构的新型人工电磁材料来实现这种透镜。这种设计方法简单灵活,对馈源天线没有限制。以经典矩形贴片天线为例,比较了贴片天线和透镜天线的回波损耗和远场方向图,结果表明运用这种方法设计的透镜使贴片天线的增益提高了2 dB,口径效率从62%提高到了99%。     

A high‐accuracy complex‐phase method of simulating X‐ray propagation through a multi‐lens system

The propagation of X‐ray waves through an optical system consisting of many X‐ray refractive lenses is considered. For solving the problem for an electromagnetic wave, a finite‐difference method is applied. The error of simulation is analytically estimated and investigated. It was found that a very detailed difference grid is required for reliable and accurate calculations of the propagation of X‐ray waves through a multi‐lens system. The reasons for using a very detailed difference grid are investigated. It was shown that the wave phase becomes a function, very quickly increasing with increasing distance from the optical axis, after the wave has passed through the multi‐lens system. If the phase is a quickly increasing function of the coordinates perpendicular to the optical axis, then the electric field of the wave is a quickly oscillating function of these coordinates, and thus a very detailed difference grid becomes necessary to describe such a wavefield. To avoid this difficulty, an equation for the phase function is proposed as an alternative to the equation of the electric field. This allows reliable and accurate simulations to be carried out when using the multi‐lens system. An equation for the phase function is derived and used for accurate simulations. The numerical error of the suggested method is estimated. It is shown that the equation for the phase function allows efficient simulations to be fulfilled for the multi‐lens system.     

Polarization-independent and high-diffraction-efficiency Fresnel lenses based on blue phase liquid crystals

A polarization-independent and high-diffraction-efficiency Fresnel lens is developed based on blue phase liquid crystals (BPLCs). The optically isotropic characteristic of BPLCs is used to produce a polarization-independent Fresnel lens. The small optical phase shift of BPLCs that is induced by the Kerr effect is sufficient for the BPLC Fresnel lens to have high theoretical and experimental diffraction efficiencies of 41% and ～34%, respectively. An electrically erasable memory effect in the focusing diffraction at an electric field E>4.44?V/μm is observed. The electro-optical properties of the BPLC Fresnel lens are analyzed and discussed.     

New monochromator of mass-spectrometric sources

A model of a new type of a monochromator for the ion beam emitted by mass-spectrometric ion sources with a broad energy distribution is considered. The ion beam monochromation was carried out by transforming the energy spectrum of particles in high vacuum by the shock effect produced by electric pulses on ions in a spatially nonuniform field followed by the formation of an ion beam in the electrostatic field of the immersion lens. Numerical simulation of the operation of the monochromator proves its performability as a compact and effective instrument for solving the problem of monochromation in mass-spectrometry.     

圆孔液晶透镜的ZEMAX设计与优化

液晶透镜是自由3D显示的新器件,其原理是利用基于向列相液晶指向矢随外加电场作用发生变化的光电特性。本文提出一种简易准确的透镜参数设计和优化方案。以单圆孔结构的液晶透镜为例,利用光学软件ZEMAX和焦距缩放法对圆孔结构的液晶透镜的参数加以设计并优化。分析液晶透镜的像差,评价成像质量。结果表明,优化后的液晶透镜的像差明显减小,3.5°视场下,弥散斑均方根半径RMS值由248.118μm减小到62.192μm,为原来的25.1%;光学调制传递函数MTF值明显改善。最后实验测试验证了液晶透镜阵列的衍射光斑亮度及清晰度均显著提高。     

Tunable microlens arrays using polymer network liquid crystal

A tunable-focus microlens array based on polymer network liquid crystal (PNLC) is demonstrated. The PNLC was prepared using an ultraviolet (UV) light exposure through a patterned photomask. The photocurable monomer in each of the UV exposed spot forms an inhomogeneous centro-symmetrical polymer network which acts as a lens when a homogeneous electric field is applied to the cell. The focal length of the microlens arrays is tunable with the applied voltage.     

大变焦范围电调谐液晶变焦透镜的研究

基于向列相液晶指向矢随施加电场作用发生变化的特性, 结合几何光学和液晶理论提出了一种液晶透镜结构模型, 研究了电极大小、隔垫物厚度等液晶透镜参数对液晶透镜焦距的影响. 通过优化参数, 得到结构简单、变焦范围较大的新型液晶透镜样品, 在驱动电压0 V_RMS–250 V_RMS下可调的焦距范围为75–230 mm, 达到155 mm.     

电场热处理条件下TiO2薄膜的晶化行为研究

利用溶胶-凝胶法和电场热处理工艺在玻璃表面制备出一层TiO₂薄膜，采用DTA ，Raman光 谱，XRD和AFM等测试手段分析了TiO₂薄膜在电场热处理过程中的晶化行为.然后 在理论上 分析了外电场对TiO₂薄膜热处理过程的影响，提出了通过引入外电场促进TiO2薄膜从无 定形到锐钛矿的相转变的方法.通过甲基橙水溶液的光催化降解实验表明：在520℃电场热处 理条件下的TiO₂薄膜的光催化效率高于未引入电场热处理的TiO₂薄 膜. 关键词： 薄膜 晶化 电场 2')" href="#">TiO₂     

Delayed electrical response of polyethylene observed in positronium formation

The transient and steady effects of positronium yield in polyethylene, due to the application and removal of an external electric field, have been studied. The time-dependent electric field effective in the Ps formation region was deduced from yield measurements.     

Far-field pattern analysis of 94 GHz extended hemispherical lens monopulse antennas

In this paper, the far-field patterns are investigated for double-slot antenna array placed on extended hemispherical lenses. The radiation patterns of the extended hemispherical lens fed by single double-slot antenna or double-slot antenna array are computed using ray-tracing inside the dielectric lens and electric and magnetic field integration on the spherical dielectric surface. The computation results show that the sharp null of the difference pattern is below -37dB.     

On the possibility of terahertz wave generation upon dense gas optical breakdown

The possibility of applying the physical principles underlying the operation of a solid-state terahertz oscillator to plasma gas-discharge media is analyzed. A new method of electromagnetic wave generation in the terahertz frequency range is proposed. It is based on the excitation of plasma-oscillation current by a static electric field in a laser spark produced by an axicon lens, followed by the radiation of an electromagnetic pulse through the Cherenkov mechanism.     

Effective ionization of air in a near-critical electric field at high temperatures

The effective ionization at the early stages of the development of an electric discharge in air at moderate and high temperatures and pressures was analyzed. Ionization in an external electric field were studied with consideration given to background electrons, the attachment and detachment of electrons from atoms and molecules, and recharging and conversion of anions. The rates of ion-molecular reactions, in particular, detachment, depend not only on the external field strength but also on the temperature. The ionization thresholds were demonstrated to decrease with increasing temperature.     

Propagation of a general-type beam through apertured aligned and misaligned ABCD optical systems

By expanding the hard-aperture function into a finite sum of complex Gaussian functions, analytical formulae for the electric field of a general-type beam propagating through apertured aligned and misaligned ABCD optical systems are derived using the generalized Collins formulae, which provide a convenient way of studying the propagation of a variety of laser beams, such as Gaussian, cos-Gaussian, cosh-Gaussian, sine-Gaussian, sinh-Gaussian, flat-topped, Hermite-cosh-Gaussian, Hermite-sine-Gaussian, higher-order annular Gaussian, Hermite-sinh-Gaussian and Hermite-cos-Gaussian beams, through such optical systems. As numerical examples, the propagation properties of a cos-Gaussian beam through an apertured aligned or misaligned thin lens are studied.     

Quasi-stationary stage of a nonequilibrium optical discharge in the field of a Bessel wave beam

The self-consistent stationary distributions of the field and plasma produced by Bessel wave beams in a gas with the ionization and Kerr nonlinearities are studied analytically. Using a stationary model based on the condition of a constant field amplitude in the ionized region, the structures are considered to be formed by Bessel beams of two types: with an azimuthal electric field equal to zero at the symmetry axis and a quasitrans-verse field having a maximum at the axis. A specific feature of the plasma channel formed in the first case is the presence of a nonionized region in its central part (tubular discharge), whose radius is independent of the incident power. In the second case, the channel is continuous. The relation is found between the incident radiation power and the external radius of the discharge. It is shown that the Kerr nonlinearity, which is especially important at small divergence angles of the beam, enhances the maximum plasma density and reduces the discharge radius. The parameters of plasma structures produced upon focusing a Gaussian beam by a conical lens are estimated using the model proposed.     

轴对称矢量光束聚焦特性研究现状及其应用

轴对称矢量光束是一种空间非均匀偏振光束, 中心光强为零, 经物镜聚焦后能在焦点附近产生空间场分量. 在高变迹系数光学系统成像情况下, 与线偏光、圆偏光相比, 径向偏振光与光瞳滤波技术及图像复原技术结合, 能获得较小焦斑, 提高横向分辨力. 介绍了轴对称矢量光束的特性, 基于电偶极子辐射模型和矢量衍射理论研究了轴对称矢量光束经高数值孔径物镜聚焦后的特性, 系统介绍了基于轴对称矢量光束实现光斑紧聚焦的几种方法, 并简述了轴对称矢量光束在差动共焦超分辨成像领域的研究设想. 关键词： 差动共焦显微技术 紧聚焦 光瞳滤波 轴对称矢量光束