光学生物学应用

Q63 2004010799 用聚苯乙烯小球模拟生物组织中的光强分布=Photonicintensity distribution sinmlations of biological tissues withpolystyrene spheres[刊,中]/郭红莲(中科院物理研究所凝聚态物理中心光物理实验室.北京(100080)),程丙英…     

用Mie氏散射理论测量聚苯乙烯微球的折射率

采用全Mie氏散射理论，计算单色平行光被该球粒散射后的光强图案分布.在实验上，把聚苯乙烯小球分散在纯净水中，使其浓度满足光的透过率为70%左右的条件，然后测量单色平行光通过该样品比色皿后的远场衍射图样的第一暗环角半径的数值大小.将该测得的角半径大小同上述采用全Mie氏散射理论计算的不同折射率下的散射光强角分布曲线图相比较，选出与测得的第一暗环角半径大小符合最好者，从而得到国家标准物质聚苯乙烯小球相对于分散剂纯净水的折射率大小，最后得到聚苯乙烯小球的折射率为1.6.本研究为该标准样品提供了一个重要光学参数.     

频域近红外光谱法研究生物组织内部光子传输特性

基于光子在生物组织中的辐射传输理论以及Feng模型,应用频域近红外光谱法研究生物组织中异质体位置的变化,对出射光的光强和相位变化的影响及规律。设计了一仿真实验,用牛奶代替强散射性质的生物组织,并在牛奶中放置一个高度可控的具有一定吸收系数和散射系数的小球。移动小球在牛奶中的高度,检测出射光的交流幅度AC、直流光强DC和相位延迟Phase的值,绘制小球位于不同深度时AC,DC和Phase的曲线,并探讨其变化规律。结果表明,随着小球在牛奶中深度的变化,光强AC,DC和相位Phase呈现一定的相关性;随着光源和检测器之间距离的增加,检测到的光强和相位曲线的波谷点均向右偏移;当小球偏离光源和检测器越远,对检测到的光强和相位的影响越小。验证了光子在生物组织中的传输规律,为用频域近红外光谱法进行组织光学参数的检测及组织中异质体位置的定位奠定了基础。     

有序金纳米颗粒阵列的制备及光吸收特性研究

采用纳米球刻蚀技术中漂移法在玻璃基片上制备较大 面积不同直径的聚苯乙烯小球掩模板, 采用磁控溅射技术在掩模板上沉积不同厚度的金薄膜, 去除聚苯乙烯小球后, 通过扫描电子显微镜观察到周期排列的三角状金纳米颗粒点阵. 通过紫外-可见分光光度计测试所制备样品的光吸收特性, 发现表面等离子体共振峰随粒径增大发生红移, 随金纳米颗粒高度增加发生蓝移. 基于Mie理论, 利用Matlab软件编程对不同粒径的金阵列光吸收特性进行理论模拟, 并与实验结果进行对比. 关键词： 纳米球刻蚀 金纳米颗粒阵列 表面等离子体共振     

聚苯乙烯微粒光子晶体的反常透过特性

在实验上发现了3μm聚苯乙烯(PS)小球光子晶体在350nm至900nm波长上的透过率的周期扰动.根据透过率曲线的周期扰动的峰谷值判断，这种周期性透过率特性是基于PS小球的whispering-gallery-mode(WGM)共振，而不是源于米氏散射或布拉格衍射.实验表明，周期性排列 小球在非带隙区域对光的传输同样有一定的影响.这一结果对光子晶体薄膜的应用提供了新 的可能性. 关键词： 光子晶体 透过率 whispering-gallery-mode共振     

磁性液体中非磁性小球与磁性纳米颗粒的相互作用及磁组装

利用磁性液体与聚苯乙烯小球溶液混合得到的复合磁性液体, 研究了聚苯乙烯小球和磁性纳米颗粒在外加磁场作用下的动力学过程. 实验结果表明, 当外加磁场的方向平行于样品平面时, 聚苯乙烯小球在沿着磁场的方向上表现出相互吸引而形成链状结构, 其动力学过程可分为聚苯乙烯小球被反磁化产生相互吸引而形成短链的快过程以及短链间相互吸引形成长链的慢过程; 当外加磁场的方向垂直于样品平面时, 相邻聚苯乙烯小球表现出排斥的相互作用而形成短程有序的二维结构, 当磁场强度增加到一定的阈值时, 聚苯乙烯小球和磁性纳米颗粒形成的团簇会产生相互吸引而组装成复合式的花瓣结构. 关键词： 磁性液体 磁组装 非磁性颗粒     

双层半无限生物组织光学背散射的MonteCarlo模拟

用MonteCarlo方法模拟了漫散射光在双层半无限生物组织中的传输，并与半无限情形相比较，给出了一定表层厚度d下，组织表面的光强值、传输深度及分布范围随着各项异性因子g、吸收系数μa以及散射吸数μs变化而变化的关系，分析了其变化原因。     

基于δ声波场的生物组织光学断层成像研究

利用δ声波场和近红外光漫射理论实现生物组织的断层成像是一种新颖医学 成像方法. 通过构建一个δ声波场并作用到生物组织中，仅改变组织内作用点上的光学特性参数，并影响近红外光在组织中的传播特性而改变组织表面的光强分布. 利用组织表面光强改变量与作用点上组织光学参数改变量之间的内在关系，可以通过对δ声波场作用点上断层的扫描实现组织内部的断层成像. 该方法具有广泛的临床医学应用前景，为乳腺癌的早期检测提供一种有效方法. 关键词： 光学断层成像 δ声波场 漫射方程 生物组织     

基于频域近红外光谱法的生物组织光学参数的检测与三维重构

生物组织的光学特性参数与组织的各种生理、生化以及病理过程密切相关。光学特性参数的检测与三维重构可以在一定程度上了解组织的内部结构及特性。基于频域近红外光谱法,使用美国ISS公司的频域近红外光谱检测系统,采用多光源多检测器技术,将830 nm的激光经过调制后,照射进放置了具有一定吸收系数和散射系数的异质体小球的牛奶中,检测出射光的光强和相位,然后应用光学扩散层析成像技术,通过计算含有异质体小球的牛奶的光学参数,重构出了牛奶中异质体的具体位置。实验结果表明,利用频域近红外光谱法得到的出射光的光强和相位信息,能够较准确地计算出牛奶及异质体小球的吸收系数和散射系数等组织光学参数,并可进一步定位出牛奶中异质体小球的位置。因此,可以考虑将该方法应用在分析及定位水果病变等农产品品质检测领域。     

基于直接胶体晶体刻蚀技术的高度有序纳米硅阵列的尺寸及形貌控制

以自组装单层胶体小球阵列为掩模，采用直接胶体晶体刻蚀技术在硅表面制备二维有序尺寸可控的纳米结构.在样品制备过程中，首先通过自组装法在硅表面制备了直径200nm的单层聚苯乙烯(PS)胶体小球的二维有序阵列；然后对样品直接进行反应离子刻蚀(RIE)，以氧气为气源，利用氧等离子体对聚苯乙烯小球和对硅的选择性刻蚀作用，通过改变刻蚀时间，制备出不同尺寸的PS胶体小球的有序单层阵列；接着以此二维PS胶体单层膜为掩模，以四氟化碳为气源对样品进行刻蚀；最后去除胶体球后得到二维有序的硅柱阵列.SEM和AFM的测量结果表明：改变氧等离子体对胶体球的刻蚀时间和四氟化碳对硅的刻蚀时间，可以控制硅柱的尺寸以及形貌，而硅柱阵列的周期取决于原始胶体球的直径. 关键词： 胶体晶体刻蚀 纳米硅柱阵列     

Second harmonic generation from closed packed hexagonal structure of nano-nickel arrays

A closed packed hexagonal structure of nickel nanoparticles was fabricated by deposition of thin nickel films on self-assembled polystyrene micron spheres, which were made of nanospherical lithography in conjunction with left-off the micro spheres. The optical second harmonic generation from these periodically arrayed nickel nanoparticles reveals intensity with a value much larger than that generated from a uniform nickel-film of the same thickness. Quasi phase matching contributed from Bragg wave vectors of the periodic arrayed nickel nanoparticles can satisfactorily express this enhancement.     

Inversion of ultrasonic scattering data for red blood cell suspensions under different flow conditions

Recent results for low-frequency scattering by correlated random distributions of nonspherical particles averaged over orientation are applied to invert ultrasonic data for red blood cell suspensions under different flow conditions. The inversion procedure isolates a correlation parameter (c) representing a process in which the volume fraction (w) of particles increases linearly, and also a cell population parameter P. Reduced data records of scattering versus hematocrit are compared with S(c;w)P, where the generalized fluctuation function S is proportional to the variance in particle number, and P is proportional to the backscattering cross section of an isolated particle. The peak scattering for the different flow processes occurs at values of w ranging from about 0.15 for the most uniform to 0.25 for the least, corresponding to c values of about 2.1 to 0.4, as compared with w approximately equal to 0.13 and c = 3 for hard (repulsive at contact) spheres or aligned ellipsoids. The lower values of c suggest weaker repulsion between the deformable cells and effective interparticle attraction (aggregative trends), and c approximately equal to 2 may also involve flow alignment of the discoids.     

Probing gluonic spin-orbit correlations in photon pair production

We consider photon pair production in hadronic collisions at large mass and small transverse momentum of the pair, assuming that factorization in terms of transverse-momentum dependent parton distributions applies. The unpolarized cross section is found to have azimuthal angular dependencies that are generated by a gluonic version of the Boer-Mulders function. In addition, the single transversely polarized cross section is sensitive to the gluon Sivers function. We present simple numerical estimates for the Boer-Mulders and Sivers effects in diphoton production at RHIC and find that the process would offer unique opportunities for exploring transverse-momentum dependent gluon distributions.     

Micromechanical simulation and analysis of one-dimensional vibratory sphere packing

We present a numerical method capable of reproducing the densification process from the so-called random loose to dense packing of uniform spheres under vertical vibration. The effects of vibration amplitude and frequency are quantified, and the random close packing is shown to be achieved only if both parameters are properly controlled. Two densification mechanisms are identified: pushing filling by which the contact between spheres is maintained and jumping filling by which the contact between particles is periodically broken. In general, pushing filling occurs when the vibration intensity is low and jumping filling becomes dominant when the vibration intensity is high.     

Simple algorithm for quantitative analysis of reflection electron energy loss spectra (REELS)

A detailed comparison of two different physical approaches for quantitative analysis of reflection electron energy loss spectra (REELS) is presented. The Tougaard–Chorkendorff (TC) algorithm [S. Tougaard, I. Chorkendorff, Phys. Rev. B35 (1987) 6570] is analyzed theoretically and applied to experimental spectra of four elemental solids (Si, Cu, Ag, and Au). A closed expression is derived for the quantity retrieved by the TC-algorithm, the so-called “effective” cross section, which was originally only given as a recursive procedure. Single scattering loss distributions are derived from the experimental spectra using the bivariate reversal method [W.S.M. Werner, Phys. Rev. B74 (2006) 075421]. The latter agree satisfactorily with density functional theory (DFT) calculations and other data found in the literature. Using these single scattering loss distributions, the TC “effective” cross section can be perfectly reproduced if the fact is taken into account that the effective cross section is not a single scattering loss distribution and is governed to a significant extent by elastic scattering. On the basis of the above results, a dramatically simplified deconvolution scheme for quantitative analysis of REELS is developed.     

The role of absorption in large-angle elastic scattering

The measurements of energy loss distributions obtained in electron scattering experiments at high momentum transfer are presented for Xe, Ar and methane. The spectra show a large variety of intensity distributions, clearly different from those obtained in measurements at the dipole limit. The fraction of the intensity present in the energy loss distribution compared to the elastic peak is significant, but is in line with the reduction of the elastic cross section due to absorption. It is argued that, if similar effects are present in the condensed phase, they should be dealt with in any quantitative analysis of electron transport in matter, as is often done using Monte Carlo simulations. This argument is worked out in some detail for Reflection Electron Energy Loss Spectroscopy.     

Spatial distribution of radiation intensity in high-frequency electrodeless discharge lamps

The spatial distribution of the intensity of radiation from high-frequency electrodeless discharge lamps of LV-2 and VSB-2 types, used as radiation sources in atomic absorption spectrometry, was investigated. Radiation intensity distributions over the cross section of the lamps were measured on the atomic and ionic lines of a buffer gas and a filler element. It is shown that in a lamp filled with buffer gas only the distribution of the intensity of atomic and ionic lines is dome-shaped, and that it is determined by the electron density distribution in the plasma as well as by the mechanism of excitation and ionization of the buffer gas. The distribution of the intensity of radiation from the filler element is strongly nonuniform, with a maximum that is concentric with the bulb walls and a minimum on the lamp axis. The observed spatial intensity distributions are explained by the redistribution of filler-element atoms over the volume of the lamp under the conditions of high electron concentrations. The time dynamics of the spatial intensity distributions during warm-up of the lamps was investigated. It is shown that the process of establishment of stationary distributions goes on nonmonotonically, which is due to the redistribution of energy among different components of the discharge plasma. Translated from Zhurnal Prikladnoi Spektroskopi, Vol. 67, No. 1, pp. 15–20, January–February, 2000.     

具有轨道角动量光束入射下的单球粒子散射研究

根据广义Mie理论,研究了具有轨道角动量拉盖尔-高斯光束（LGB）的空间传输特性以及单粒子散射特性.在单体球粒子对高斯光束散射研究的基础上,分析了在自由空间不同传输距离LGB光束的光强分布情况,在不考虑散射和波束相移关系的情况下,将LGB作为入射高斯光束,通过对波束入射时的散射衰减截面求解得到波束因子,利用矢量球谐函数对入射高斯波束进行展开,从而研究了单球粒子在在轴条件下对具轨道角动量高斯波束入射的散射问题.通过数值计算,讨论了散射强度及角分布在不同波束宽度情况下对其散射特性的影响,并与平面波的情况做了对比.结果表明,当波束束腰半径较小时,束腰半径对衰减率的影响较大,而当束腰半径远大于粒子半径时,接近于平面波的情况. 关键词： 广义Mie理论 轨道角动量 Laguerre-Gauss光束 单球粒子     

Simulation supported description of the local doping formation using laser chemical processing (LCP)

We present an enhanced model to describe the physics of laser chemical processing (LCP), a liquid jet guided laser technique, for local doping processes applied to crystalline silicon solar cells. The main improvement of the numerical model is the consideration of the inhomogeneous laser light intensity profile within the liquid jet cross section. Measurements of the intensity profile show local superelevations of up to factor five compared to the average intensity. A measured intensity profile was implemented into the numerical model and yields good agreement between simulated and measured dopant distributions. Inhomogeneities of the spatial dopant distribution are observed and their impact on LCP line scans for producing doped lines is investigated with respect to solar cell manufacturing.     

The single diffractive component in hadron-hadron collisions within the two-component Dual Parton model

The single diffractive component in hadronhadron interactions is studied in the two-component Dual Parton Model. We distinguish high mass single diffraction represented by a triple-Pomeron exchange and low mass single diffraction described via a two channel eikonal method. The calculated single diffractive cross sections, and the distributions agree quite well with data from collider and fixed target experiments. The fit of the model parameters to cross section data gives a extrapolation of the total, elastic, and single diffractive cross sections to supercollider energies which depends on the parton structure functions used for the minijet component.