Development of Methods to Determine the Infrared-Optical Properties of Polymer Films

Summary: In this paper, two methods for the determination of infrared optical properties of thick polymer films, based on FTIR spectroscopy, were implemented and used. Complex index of refraction data were generated for various ethylene copolymer films. Transmittance and reflectance spectra were measured in the mid infrared range using a gold-coated 100 mm-diameter integrating sphere. For the investigated films n and k values ranging from 1.3 to 1.6 and from 10⁻⁴ to 0.25 were determined, respectively. Regarding n, a good agreement was obtained for both methods, the transmittance/reflectance procedure (T/R method) used for transparent and semitransparent regions, and Single Substractive Kramers-Kronig (SSKK) algorithm applied for non-transparent regions. The highest k values were determined for the CH₂ stretching vibration. The k values are dependent on comonomer content and film thickness. The combination of both methods allows for an accurate determination of n and k in the entire IR region relevant for solar application.     

大口径KDP晶体折射率非均匀性检测

KDP晶体的折射率不均匀性将导致光束的空间分布存在不同程度的相位失配,从而使得三倍频系统的转换效率下降。为了得到KDP晶体折射率非均匀性的高精度检测结果,基于正交偏振干涉法,采用ZYGO MST大口径干涉仪,测量得到了大口径KDP晶体折射率非均匀性分布,其测量精度达到10-7,并通过实验研究了晶体面形对测量结果的影响。对晶体e光折射率非均匀性的高精度检测,为大口径晶体材料生长工艺、加工工艺等改进和提高提供了定量的检测依据。     

Acoustic metasurface for refracted wave manipulation

Here we present a design of a transmitted acoustic metasurface based on a single row of Helmholtz resonators with varying geometric parameters. The proposed metasurface can not only steer an acoustic beam as expected from the generalized Snell's law of refraction, but also exhibits various interesting properties and potential applications such as insulation of two quasi-intersecting transmitted sound waves, ultrasonic Bessel beam generator, frequency broadening effect of anomalous refraction and focusing.     

饱和非线性效应对负折射材料中孤子自频移的影响

以描述负折射材料中包含拉曼效应的高阶非线性薛定谔方程为模型,采用分步傅里叶算法数值分析了高阶效应,尤其是饱和非线性效应对自聚焦负折射率材料中的孤子拉曼自频移的影响。结果表明,在自聚焦负折射率材料中饱和非线性效应使孤子拉曼自频移速度加快;饱和非线性效应与负的自陡效应共同作用进一步加快孤子自频移的速度;饱和非线性效应同正的自陡效应、三阶色散效应共同作用时孤子拉曼自频移在整体上受到抑制。     

Thorough small‐angle X‐ray scattering analysis of the instability of liquid micro‐jets in air

Liquid jets are of interest, both for their industrial relevance and for scientific applications (more important, in particular for X‐rays, after the advent of free‐electron lasers that require liquid jets as sample carrier). Instability mechanisms have been described theoretically and by numerical simulation, but confirmed by few experimental techniques. In fact, these are mainly based on cameras, which is limited by the imaging resolution, and on light scattering, which is hindered by absorption, reflection, Mie scattering and multiple scattering due to complex air/liquid interfaces during jet break‐up. In this communication it is demonstrated that synchrotron small‐angle X‐ray scattering (SAXS) can give quantitative information on liquid jet dynamics at the nanoscale, by detecting time‐dependent morphology and break‐up length. Jets ejected from circular tubes of different diameters (100–450 µm) and speeds (0.7–21 m s^?1) have been explored to cover the Rayleigh and first wind‐induced regimes. Various solvents (water, ethanol, 2‐propanol) and their mixtures have been examined. The determination of the liquid jet behaviour becomes essential, as it provides background data in subsequent studies of chemical and biological reactions using SAXS or X‐ray diffraction based on synchrotron radiation and free‐electron lasers.     

改变光子晶体表面结构对负折射透射光强的影响

以砷化镓圆形介质柱在空气中构成二维六边形排列结构的光子晶体为例,利用时域有限差分法模拟研究了光子晶体表面结构改变对负折射透射光强的影响.模拟结果表明：针对同一结构光子晶体,在可产生负折射现象的入射光频率范围,改变光子晶体表面两侧圆形介质柱的半径和顺向侧移两侧表面最外层圆形介质柱都会均对负折射透射光强产生影响.     

“绿色”液体激光介质的非线性光学特性研究

 利用氧化钕和盐酸为原料制得Nd(phen)2Cl3(三氯二邻菲罗啉合钕),测得其光谱特性并以稀土氧化钕、苯甲酸和邻菲罗啉为原料制得绿色液体激光介质钕离子的配合物——NdB3phen（三苯甲酸—邻菲罗啉合钕）.利用飞秒激光器,采用单光束Z-扫描法研究了NdB3phen的三阶非线性光学特性.结果表明:当入射飞秒激光脉冲波长为400 nm,峰值功率密度为2.94×1014 W/m2,脉宽为117 fs时,测得样品NdB3phen的非线性折射率为－2.84×10－18 cm2/W|NdB3phen在开孔条件下呈现反饱和吸收现象,测出双光子吸收系数的值为9.11×10－12 m/W.实验结果表明,NdB3phen的双光子吸收系数和非线性折射率随着光强的增强而增大.     

Physics and applications of photonic crystals

In this article, we investigate how the photonic band gaps and the variety of band dispersions of photonic crystals can be utilized for various applications and how they further give rise to completely novel optical phenomena. The enhancement of spontaneous emission through coupled cavity waveguides in a one-dimensional silicon nitride photonic microcrystal is investigated. We then present the highly directive radiation from sources embedded in two-dimensional photonic crystals. The manifestation of novel and intriguing optical properties of photonic crystals are exemplified experimentally by the negative refraction and the focusing of electromagnetic waves through a photonic crystal slab with subwavelength resolution.     

Broadband and high efficiency terahertz metasurfaces for anomalous refraction and vortex beam generation

The applications of metasurfaces are currently a highly active research field due to their extraordinary ability to manipulate electromagnetic waves. The ultra-thin characteristics of metasurfaces allow the miniaturization and integration of metasurface devices. However, these devices work typically under a low efficiency and narrow bandwidth condition. In this work, we design eight multilayered unit cells with similar amplitudes and a phase interval of π/4, which convert the polarization states of the terahertz (THz) waves between two orthogonal directions. The average cross-polarized transmission amplitudes of these cells are all around 0.9 in an ultra-broad frequency range from 0.5 THz to 1.4 THz. Furthermore, unit cells are used to construct both an ultra-thin anomalous refraction metalens and a vortex phase plate. Our simulation results show that the anomalous refraction for the transmitted linear polarization component is comparable to the theoretical prediction, and the maximum error is determined to be below 4.8%. The vortex phase plate can also generate an ideal terahertz vortex beam with a mode purity of 90% and more. The distributions of longitudinal electric field, intensity, and phase illustrate that the generated vortex beam has excellent propagation characteristics and a weak divergence. Simulations of the two types of metasurface devices, based on the eight unit cells, exhibit very high efficiencies in a wide bandwidth. Our research will assist in the improvement in the practical applications of metasurfaces. It also provides a reference for the design of high efficiency and broadband devices that are applied to other frequency ranges.     

惠更斯作图法分析双折射中e光的反常现象

在单轴晶体双折射中,e光会发生一些反常的折射现象如负折射、e光离散角、全反射现象等.与文献中普遍所采用的基于平面光波在晶体中传播的电磁理论特性求解的过程不同,本文则以更为直观的惠更斯作图法为出发点,利用几何求解,得出负反射临界角、e光离散角、全反射临界角,并加以说明和讨论.