Experimental investigation of one-sided optical transparency in cholesteric liquid crystal thin film

Influence of boundary conditions on optical properties of a layer of cholesteric liquid crystal (CLC) has been investigated. In particular, a sample was obtained which is transparent for circularly polarized light incident from one side and gives losses in the transmission spectrum (within nearly 100 nm wide wavelength range) if light is incident from the opposite side, i.e. exhibits optical diode behavior. Two selective reflection bands were detected in the reflection spectrum of the sample. Spectral position of both selective reflection bands and transmission spectrum are shown to be CLC temperature-controllable.     

Integrating sphere study of the optical properties of aluminum nanoparticles in tetranitropentaerytrite

The dependences of the transmission coefficients and the sum of the transmission and absorption coefficients for light with a wavelength of 643 nm in compressed pentaerythritol tetranitrate (PETN) samples containing aluminum nanoinclusions (average radius of 50 nm) on the pellet thickness and the mass fraction of aluminum nanoparticles in it are studied with an integrating sphere. The light absorption and scattering in this system is simulated using the Mie theory and a radiative transfer equation. The depth profile of absorbed energy in a sample is shown to approximately obey the Bouguer-Beer law. The effective cross section of radiation absorption by aluminum nanoparticles, which takes into account both light absorption and scattering by an ensemble of nanoparticles, exceeds the geometrical cross section.     

A step forward in the study of the electroerosion by optical methods

This work develops two theoretical models of surfaces to explain the behavior of the light scattered by samples that suffers some alteration.

In a first model, it is evaluated the mean intensity scattered by the sample, analyzing the different curves obtained as function of the eroded/total surface ratio. The theoretical results are compared with those obtained experimentally. It can be seen that there exists a strong relation between the electroerosion level and the light scattered by the sample.

A second model analyzes a surface with random changes in its roughness. A translucent surface with its roughness changing in a controlled way is studied. Then, the correlation coefficient variation as function of the roughness variation is determined by the transmission speckle correlation method. The obtained experimental values are compared with those obtained with this model.

In summary, it can be shown that the first- and second-order statistics properties of the transmitted or reflected light by a sample with a variable topography can be taken account as a parameter to analyze these morphologic changes.     

用分光光度法研究非晶硅薄膜的光学性质

提出了一种测量薄膜透射光谱的方法.该方法用自制的夹具改进了分光光度计,保证了在测量大小不同的样品时参考光的强度和入射到待测样品上光的强度相同.利用改进后的分光光度计测量了沉积在玻璃衬底上非晶硅薄膜的透射光谱,并对透射光谱进行了拟合和计算,确定出非晶硅薄膜的光学常量和厚度.     

The influence of hole shape on enhancing transmission through subwavelength hole arrays

The extraordinary light transmission through a 200-nm thick gold film when passing through different subwavelength hole arrays is observed experimentally. The sample is fabricated by electron beam lithography and reactive ion etching system. A comparison between light transmissions shows that the hole shape changing from rectangular to diamond strongly affects the transmission intensity although both structures possess the same lattice constant of 600,nm. Moreover, the position of the transmission maximum undergoes a spectral red-shift of about 63,nm. Numerical simulations by using a transfer matrix method reproduce the observed transmission spectrum quite well.     

Breakdown of glass composites with a TiO<Subscript>2</Subscript> nanodimensional coating by laser ablation

The laser-ablation-induced breakdown of glass composites with nanodimensional coatings obtained by the sol–gel method is studied. It is found that the threshold energy of breakdown depends on the refractive index and light transmission coefficient of the sample. It increases with the refractive index and decreases with decreasing the light transmission coefficient in the range 400–900 nm. This can be explained by the difference in the reflection coefficients of the samples.     

Light transmission in porous silicon dioxide filled with liquids of different refractive indices

Optical transmission at 532 nm from nonabsorbing disordered porous silicon dioxide has been studied experimentally. The transmission behaviors can be adjusted by filling the pores with liquids of different refractive indics, which are analyzed based on the theory of diffusion in a weak scattering regime. In our experiment, the transmission coefficient changes from a value less than 1% to one that is greater than 75%, that is, the opaque sample becomes transparent, which means that the transport mean free path of light within the material has been effectively adjusted. In addition, this method is a useful nondestructive method to derive the refractive index of an unknown bulk porous material.     

小尺寸样品CARS图像信号分布实验研究

通过设计实验与分析模型,研究相干反斯托克斯拉曼散射成像对于样品尺寸小于系统点扩展函数尺寸的情况,分析相干反斯托克斯拉曼散射图像周围的depth的形成原因。分析过程首次引入轴向传输动态位移光线（此光线由相干体积元内轴心光线抽象出）对球形或柱形样品直径小于系统点扩展函数横向与轴向尺寸进行建模解析,对于所建模型定量分析结果表明,对于样品尺寸小于系统点扩展函数尺寸样品折射率调制了有效作用深度。Gouy相移只是其表观现象,是一个伴随性特征,因为物理学中存在的另一个极端,当样品尺寸足够小且具有相当的折射率,Gouy相移的作用近似为0,此时,样品周围的depth主要与样品的折射率及系统相干层析体积元内有效作用长度有关,相干反斯托克斯拉曼散射参量信号,具有自身的波矢匹配条件,不仅有大小,有方向,而且还受到样品自身材料折射率的影响比较明显。也就是对于参量过程波矢匹配条件是因,Gouy相移是伴随性特征。自此,通过相干反斯托克斯拉曼散射间接说明所用的紧聚焦参量信号成像过程,正是因为波矢匹配条件的存在使二次信号继承了激发光的紧聚焦特性,而拥有了继承性的Gouy相移,结合实验结果采用物理学的极端假设表明,Gouy相移不是产生depth的主要原因,主要原因是样品及周围的环境的折射率与系统相干层析体积元内有效作用长度之间共同作用的结果。而实验结果与模型定量分析的结果相吻合,此实验帮我们找到了影响CARS图像样品周围depth的成因机制,对于其他小尺寸样品的参量成像结果的分析具有一定的借鉴意义。通过设计实验,结合定量模型分析,首次明确造成小尺寸样品CARS图像周围的depth的真正原因,此抽象模型的拓展性对纳观参量过程的分析具有得天独厚的优势。抽象出的主能量光线动态位移模型成功分析纳观成像结果表明,相干作用长度之内有效作用长度及其行进路径的过程论的主因分析方法是研究纳观作用机制的最佳方法。     

利用散射光增强弱吸收固体混合物中主要光吸收物质的光声光谱特征

在传统的透射和反射光谱中, 散射光通常是误差的主要来源之一, 然而对光声光谱, 散射光有可能成为促进光谱测量的积极因素. 本文研究了弱吸收固体混合物–-奥氮平药片及其粉末的光声光谱. 为了排除光声池吸收散射光所产生背景光声信号的干扰, 取试样与其空白物的差值谱进行碳黑归一化, 得到了只与试样自身性质相关的归一化光声光谱.实验发现通过将药片碾成粉末, 可以使奥氮平药片的主成分奥氮平原料药的光声光谱特征凸显出来. 分析表明光散射效应是这一现象产生的主要原因. 传统光谱技术的障碍–-散射光却能促进光声光谱测量, 这显示出光声技术在光谱测量领域的独特优势. 上述实验提供了一种初步快速鉴别弱吸收固体混合物中少量光吸收物质的新方法, 这一方法有望应用于固体药物、矿物和土壤分析等领域. 关键词： 光声光谱 散射光 弱吸收固体混合物 奥氮平     

Optical bistability in a photonic crystal with a liquid-crystal defect

We investigate experimentally the nonlinear transmission of a photonic crystal with a nematic liquid-crystal defect upon reorientation of the director in a field of cw laser radiation propagating at a certain angle to the sample. At different detunings, we observed the regimes of bistability, differential gain, and optical limiting. The resonance transmission peaks were detuned from the laser radiation wavelength by changing the angle of light incidence onto the sample. The value of nematic nonlinear constant n ₂ determined from the experimental data is in good agreement with the theoretical estimate.     

利用折射光场分析液滴中光传播规律

为了保证液滴分析技术的重复性和可靠性,必须对光在液滴中的传播规律有更为深入的了解.设计并制作了三套不同方位的实验系统,以纯净水作为实验样品.分别拍摄了自液滴中向三个方向的折射光场分布.通过分析折射光线分布,并利用光纤出射光场的实验规律,进一步得出光在液滴中的传播轨迹,解释了光纤液滴指纹图中峰值形成过程.实验结果表明,光纤液滴指纹图中不同的特征峰值所对应的光在液滴中的传播模式是不同的.     

Far-infrared spectroscopy by synchrotron radiation at the UVSOR Facility

At the UVSOR Facility, Institute for Molecular Science, the practical use of the synchrotron radiation as a far-infrared light source has started. A spectroscopic system has been constructed at the beam line BL6A1 of UVSOR storage ring, which covers the wavenumber region from 5 to 250 cm^–1. The cross sectional diameter of the light beam at the sample position is as small as 3 mm with the angular divergence of about 100 mrad. The system has been made mainly for the transmission and reflection measurements of small samples with small angular divergence by the use of the high brightness of the synchrotron radiation. Examples of observed transmission and reflectivity spectra are shown.     

Use of transmitted color to calibrate the thickness of silicon samples

In preparing silicon-based semiconductors for transmission electron microscopy (TEM), it has been widely observed that a backlit silicon sample displays a series of colors in the thinnest regions. These colors results from absorption and optical interference of light within the silicon sample and depend upon the type of light source and the silicon sample thickness. These colors can range from deep red for thickness ≥5 μm, through orange and yellow in the thinner regions, to essentially colorless at the thinnest regions. In this work we present the first direct measurement of silicon color versus thickness and discuss the factors that influence this relationship.     

Long-range correlations of the polarized-light intensity in disordered samples

The spatial correlation function of intensity fluctuations in a speckle formed by polarized light multiply scattered in a disordered sample has been calculated. The dependence of the long-range spatial correlations on the polarization state of incident light and the depolarizing properties of the medium has been determined for the cases of transmission and reflection.     

87Rb D1线法拉第反常色散光学滤波

为了得到在高背景噪音下对弱信号光的提取,实验研究了基于⁸⁷Rb D₁线5S_1/2F=2→5P_1/2 F'=1跃迁的795 nm法拉第反常色散光学滤波器.充铷的样品池所含⁸⁷Rb的比例高于自然铷,样品池处在均匀的磁场中并且夹在两个相互正交的偏振片之间.入射的探测光通过样品池,与原子相互作用,由于法拉第旋转效应实现滤波功能.改变实验条件,透射结果随之明显变化.当温度从340 K升高到360 K,透射谱的变化情况被细致记录,并且分析了导致透射情况变化的原因.在适当的工作温度以及磁场条件下,得到线宽为约220 MHz的超窄带透射谱线,谱线透过率约为48%.⁸⁷Rb D₁线的实验结果优于⁸⁵Rb的吸收线.     

变色磷灰石的可见光光谱特征研究

磷灰石是珠宝市场上常见的宝石品种,因颜色丰富而广受欢迎。变色磷灰石是稀有品种且价格高昂,该品种在D65光源（色温6 500 K）下呈黄绿色,A光源（色温2 856 K）下呈粉红色,其可见光光谱的谱学特征与变色成因未被详细研究。基于此,将一颗变色磷灰石晶体,沿其平行c轴和垂直c轴方向各切下一个薄片并双面平行抛光,分别测试其可见光光谱与微量元素。结果发现,其可见光光谱中谱峰较多：位于583和578 nm处的吸收双峰强度最强,位于748和738 nm处的吸收双峰强度中等,分别位于688和526 nm处的吸收峰,强度较弱。还有一些非常微弱的吸收峰,分别位于514,483,473和443 nm处。位于748和738 nm处的吸收双峰与583和578 nm处的吸收双峰共同造成了红橙光区的透射窗,583和578 nm处的吸收双峰与526 nm处的吸收峰共同造成了黄绿光区的透射窗。D65光源和A光源由于相对光谱功率分布不同,在不同透射窗的透过有所不同,导致变色磷灰石在不同光源下呈现出不同颜色。D65光源中黄绿光成分较多,透过黄绿光区透射窗的成分较多,D65光源下磷灰石呈黄绿色,A光源中红光成分较多,通过红橙光区透射窗的成分较多,A光源下磷灰石呈粉红色。因此,磷灰石的变色效应与位于748和738 nm处的吸收双峰,位于583和578 nm处的吸收双峰以及位于526 nm处的吸收峰相关。根据微量元素数据与稀土元素的晶体场理论,这些吸收峰是由稀土元素钕（Nd）导致。根据不同晶体方向样品的可见光光谱特征,平行c轴方向变色效果更好,建议加工变色磷灰石晶体时宝石台面应尽量平行c轴。该研究结合微量元素与可见光光谱分析了变色磷灰石的变色成因,并为其加工切割方向提供了指导。     

Generalized ellipsometry in unusual configurations

Most ellipsometry experiments are performed by shining polarized light onto a sample at a large angle of incidence, and the results are interpreted in terms of thin film thicknesses and isotropic optical functions of the film or substrate. However, it is possible to alter the geometrical arrangement, either by observing the sample in transmission or at normal-incidence reflection. In both cases, the experiment is fundamentally the same, but the interpretation of the results is considerably different. Both configurations can be used in conjunction with microscope optics, allowing for images to be made of the sample. The results of three examples of these different configurations using the two-modulator generalized ellipsometer (2-MGE) are reported: (1) spectroscopic birefringence measurements of ZnO, (2) electric field-induced birefringence (Pockels effect) in GaAs, and (3) normal-incidence reflection anisotropy of highly oriented pyrolytic graphite (HOPG).     

Optical transmission and reflection spectroscopy of single quantum dots

An analytical formulation of the interband optical transmission and reflectivity spectra of a single quantum dot embedded in a semiconductor is presented. We consider the effect of the sample surface as well as other reflecting surfaces on the shape of the spectra near the ground state exciton resonance. The saturation of the transmission and reflectivity spectra due to the quantum optical saturation of the transition at higher light power is presented.     

Spatial quantum correlations in multiple scattered light

We predict a new spatial quantum correlation in light propagating through a multiple scattering random medium. The correlation depends on the quantum state of the light illuminating the medium, is infinite in range, and dominates over classical mesoscopic intensity correlations. The spatial quantum correlation is revealed in the quantum fluctuations of the total transmission or reflection through the sample and should be readily observable experimentally.     

Interaction of ultrashort elliptically polarized laser pulses with nonlinear helical photonic metamaterial

The effect of nonlinear properties of a material with a periodic structural cell (three-dimensional spiral) on the specificity of transmission and reflection of elliptically polarized laser pulses normally incident on the metamaterial is studied using the finite-difference time-domain method. An analysis of the hodograph of electric-field strength vector showed that an increase in the peak intensity of a linearly polarized laser pulse incident on a sample leads to an increase in the orthogonal component of the electric-field strength vector in the pulse transmitted through the medium. When pulses containing few electric-field periods are incident on a metamaterial, the latter demonstrates radically different optical properties for right- and left-handed circularly polarized light passing through the medium. It was shown that an increase in the intensity of a right-handed (left-handed) circularly polarized ultrashort pulse, incident on a sample composed of a rather large number of right-handed (left-handed) spirals made of nonlinearmaterial, widens the frequency range within which the incident light is almost entirely reflected from the medium.