单颗粒气溶胶的吸湿增长模型及散射特性研究

为研究亲水性和疏水性气溶胶的吸湿性差异引起的散射特性差异,基于热力学原理和表面吸附理论分别建立了两类气溶胶的吸湿增长模型,并利用离散偶极子近似方法计算了相对湿度为40%～90%范围内两类气溶胶的散射性质。结果表明:亲水性粒子(以4种典型的无机盐为例)达到潮解点时,粒径随相对湿度的增大呈指数增长;而疏水性粒子(以烟尘为例)的粒径随着相对湿度的增加呈现非线性缓慢增长,该结果与实验测量值基本吻合。利用上述吸湿增长模型及实测的折射率-湿度增长规律,计算分析了在粒径为0.1～1.0μm的范围内,相对湿度与气溶胶粒子散射增长因子的关系。研究发现,潮解后亲水性粒子散射增长因子呈指数增长,相对湿度为90%时,其值增大了几十倍,且氯化钠无机盐的散射因子增长曲线与实验结果吻合较好;而疏水性粒子的散射增长因子最大增至1.07,远小于亲水性粒子的数值。上述结果为气溶胶气候效应的评估、气溶胶浓度和大气能见度的精确测量提供了一定的理论支持。     

过滤电弧沉积非晶金刚石薄膜的光谱椭偏研究

为了深入理解过滤阴极电弧沉积非晶金刚石薄膜的光学性质,利用光谱椭偏仪研究了薄膜光学常数随测试偏振光波长变化的谱学关系,进而分析了薄膜折射率、消光系数和光学带隙与沉积能量之间的变化规律.实验表明,非晶金刚石薄膜的折射率高于金刚石晶体的折射率,薄膜的吸收光谱在高吸收区可以用抛物线型函数描述,并由此计算Tauc带隙.随着波长向红外延伸,非晶金刚石薄膜的消光系数渐次降低并趋近于零,光学常数因沉积能量变化而实现的调整幅度也逐渐缩小.随着衬底偏压的增加,折射率和光学带隙都是先升高后减小,并在负偏压为80 V时有最大值;而消光系数却是先减小再升高,在负偏压为80 V时有最小值.     

激光雷达遥感地表气溶胶消光吸湿因子及其对波长的依赖特性

介绍了一种在开放大气环境下、利用水平探测的双波长-偏振米氏散射激光雷达遥感地表气溶胶消光吸湿增长因子的新方法。在激光雷达垂直观测气溶胶吸湿性质相关研究报道的数据筛选方法的基础上,利用消光系数与实测相对湿度(RH)之间的强相关性,以及实测的粒子质量浓度和粒子退偏振比的变化规律作为判据,说明吸湿增长作用是引起地表气溶胶消光系数增大的主要原因。相比于激光雷达垂直方法观测气溶胶吸湿性质,该筛选过程更加严格地约束了激光雷达水平观测吸湿性质的筛选判据,且对气象条件的约束相对简单。利用筛选得到的有效数据,计算得到气溶胶消光吸湿增长因子,并分析其对波长的依赖特性。观测结果表明,在开放大气条件下,合肥地区粒子谱分布可能会出现单模态、双模态甚至多模态的复杂情况,导致Angstrom波长指数与相对湿度之间的变化规律表现为正相关、负相关和不相关3种结果;同样也导致短波的气溶胶消光吸湿增长因子弱于、等于或强于长波的气溶胶消光吸湿增长因子的多样性现象。     

北京奥运前期典型天气喇曼激光雷达观测研究

以自行研制的双波长三通道拉曼激光雷达、振荡天平(PM10、PM2.5)、碳黑(BC)气溶胶分析仪及能见度仪相结合对"好运北京"2008年奥运会前期典型天气状况进行了测量与分析,给出了北京奥运主场馆上空气溶胶消光系数的垂直分布及其时空变化关系,计算了气溶胶的消光散射比,并分析了灰霾天气条件下大气能见度、气溶胶颗粒物PM10、PM2.5、BC及气溶胶消光系数垂直分布之间的相互关系.研究结果表明,灰霾天气条件下,大气能见度、颗粒物质量浓度与气溶胶颗粒物消光系数之间具有直接的相关性.     

PM2.5气溶胶光学特性研究

利用FA-3型Anderson撞击式气溶胶粒度分布采样器采集大气中的可吸入颗粒物。在实验室使用光学测量系统对粒径低于PM2.5的气溶胶颗粒物进行透过率测量。结果表明,透过率随气溶胶粒子粒径的增大具有逐渐增加的趋势。粒径低于PM2.5的气溶胶颗粒与PM10粒径范围内的透过率相比,具有明显的波长选择性。     

大气气溶胶消光特性和折射率的测量

 介绍了一种综合利用能见度仪、微脉冲激光雷达和光学粒子计数器测量大气气溶胶折射率的新方法。首先使用能见度仪和激光雷达测量出大气气溶胶的消光系数和消光后向散射比，然后使用粒子计数器测量出粒子谱分布，结合气溶胶粒子折射率，根据球形粒子的米（Mie）散射理论，可以得到气溶胶消光系数和消光后向散射比。通过分析消光系数、消光后向散射比、粒子谱分布和折射率之间的关系，结合已知的消光系数和消光后向散射比，反演出大气气溶胶粒子的折射率。     

磁控溅射制备铬薄膜的结构和光电学性质

用直流磁控溅射技术在石英基片上制备不同厚度(5 nm~114 nm之间)的铬膜.使用X射线衍射仪和分光光度计分别检测薄膜的结构和光学性质,利用德鲁特模型和薄膜的透射、反射光谱计算铬膜的厚度和光学常量,并采用Van der Pauw方法测量薄膜电学性质.结果表明:制备的铬薄膜为体心立方的多晶态,随着膜厚的增加,薄膜的结晶性能提高,晶粒尺寸增大;在可见光区域,当膜厚小于32 nm时,随着膜厚的增加,折射率快速减小,消光系数快速增大,当膜厚大于32 nm时,折射率和消光系数均缓慢减小并逐渐趋于稳定;薄膜电阻率随膜厚的增加为一次指数衰减.     

磁控溅射制备铬薄膜的结构和光电学性质(英文)

用直流磁控溅射技术在石英基片上制备不同厚度(5nm～114nm之间)的铬膜.使用X射线衍射仪和分光光度计分别检测薄膜的结构和光学性质,利用德鲁特模型和薄膜的透射、反射光谱计算铬膜的厚度和光学常量,并采用Van der Pauw方法测量薄膜电学性质.结果表明:制备的铬薄膜为体心立方的多晶态,随着膜厚的增加,薄膜的结晶性能提高,晶粒尺寸增大;在可见光区域,当膜厚小于32nm时,随着膜厚的增加,折射率快速减小,消光系数快速增大,当膜厚大于32nm时,折射率和消光系数均缓慢减小并逐渐趋于稳定;薄膜电阻率随膜厚的增加为一次指数衰减.     

北京奥运前期典型天气拉曼激光雷达观测研究

以自行研制的双波长三通道拉曼激光雷达、振荡天平（PM10、PM2.5）、碳黑（BC）气溶胶分析仪及能见度仪相结合对“好运北京”2008年奥运会前期典型天气状况进行了测量与分析,给出了北京奥运主场馆上空气溶胶消光系数的垂直分布及其时空变化关系,计算了气溶胶的消光散射比,并分析了灰霾天气条件下大气能见度、气溶胶颗粒物PM10、PM2.5、BC及气溶胶消光系数垂直分布之间的相互关系。研究结果表明,灰霾天气条件下,大气能见度、颗粒物质量浓度与气溶胶颗粒物消光系数之间具有直接的相关性。     

Cr1-xNbxSi2固溶体弹性性质、电子结构和光学性质的理论研究

采用基于密度泛函理论(DFT)的第一性原理计算，对Nb掺杂CrSi2的晶格结构、弹性性质，电子结构和光学性质进行了系统的研究. 研究结果表明：随着Nb掺杂浓度增加，弹性常数、体变模量、剪切模量、杨氏模量均减小，而且能带间隙也逐渐减小，表现为p型掺杂特点. 基于电子结构计算结果以及已知的实验结果, 讨论了Nb掺杂CrSi2后对其复介电函数、折射率、消光系数、反射率和吸收谱等光学性质的影响.     

Optical Cross-Sections of Soot Agglomerates: The model of the virtual refractive index and first-order multiple scattering

A new technique for the calculation of the optical properties of agglomerated spherical primary particles is presented. By means of the so-called virtual refractive index, the multiple scattering within the agglomerate is decribed by a modified Mie solution, thus avoiding restrictions with respect to the primary particle size. An additional benefit of the method is the small numerical expense required, permitting practical use for complex agglomerate structures such as real combustion aerosols. Utilizing this method, attention is focused on the calculation of the extinction cross-section of real combustion aerosols in order to discuss the results of multiple-wavelength extinction measurements within combustion systems. It is found that approximately the primary particle diameter is determined. Furthermore, the error that occurs can be avoided by means of the method presented without a detailed knowledge of the agglomerate size. Thus, the present work eliminates some current uncertainties inherent in optical combustion aerosol characterization.     

球形雾霾粒子的紫外光散射偏振特性研究

在我国经济社会快速发展的同时,雾霾天气成为了突出的环境问题,雾霾粒子的测量非常重要。偏振紫外光与大气雾霾粒子发生散射后,散射光偏振状态(Stokes矢量以及偏振度)的改变能反映雾霾粒子的相关物理特性(粒径、复杂折射率等)。基于Mie散射理论建立了紫外光雾霾球形粒子直视和非直视单次散射模型,研究了单个球形粒子和链状结构球形粒子物理特性的改变对散射光偏振状态的影响,并用蒙特卡洛仿真分析已知粒径分布的雾霾粒子浓度对散射光偏振状态的影响。结果表明:针对单个球形粒子,随着粒子粒径的增大Stokes矢量中散射光光强(I_s)随之增强,粒子复折射率虚部为先增大后较小,偏振度也是在不断增大,且复折射率虚部较小时,偏振度增加趋势快;对于粒径分布不变的雾霾粒子,随着粒子的浓度增加,雾霾粒子的散射系数、消光系数和吸收系数均呈线性增加,但是I_s先增大后减小。针对链状球形粒子,随着粒子个数的增加,I_s均呈现增大的趋势,且偏振度可用于区分链状球形粒子是否由相同球形粒子组成;相同球形粒子组成链状结构中,I_s随着粒子数量的增加而线性增大,偏振度不改变;不同球形粒子组成的链状结构,I_s以及偏振度的变化趋势可以区分粒子物理特性。     

散射相函数的高阶光学参量研究

漫反射光谱技术被广泛应用于无创测量生物组织光学性质。当光源与探测器很近时,仅仅依靠吸收系数μ_a和约化散射系数μ′_s不能准确描述光源附近光的传播状态。而二阶光学参量γ的引入改善了近光源光的传播状态的描述。本文将生物组织的散射等效成特定球形颗粒的散射,基于Mie散射理论,计算了与散射相函数p(θ)有关的单粒子和多分散系粒子的二阶光学参量γ,研究了γ随尺度参数α和相对折射率m的变化规律,描述了γ与组织结构参量之间的联系,并阐述了γ对粒子特征的表征能力。研究表明,参量γ对尺度参数α小于2的微粒尺寸的改变是敏感的,并呈二次函数关系,其系数与相对折射率呈线性关系;对于相对折射率和尺度参数都不相同的两个粒子,他们的各向异性因子g相同时,二阶光学参量γ却不同,粒子越大,γ表征粒子特征的能力越强。这对于无创探究组织微观形态具有深远的意义。     

空间垂直方向气溶胶消光特性的研究

在已知大气气溶胶折射率和气溶胶谱分布的基础上,对空间垂直方向的气溶胶消光特性进行了研究。文章利用Mie散射理论计算讨论了气溶胶的消光、散射、吸收系数随各参数的变化,并在MATLAB中对变化情况进行了仿真。结果表明,粒子半径与入射波长大小相近时气溶胶的消光最强,并且随着能见度的增大,气溶胶衰减系数减小。这些结论可以为红外辐射的大气衰减计算和分析提供依据。     

Optical constants of Na-doped ZnO thin films by sol-gel method

The structural and optical properties of pure and Na-doped ZnO thin films have been investigated by X-ray diffraction (XRD), atom force microscopy and UV-Vis spectrophotometer. The crystal structure of all the thin films is the hexagonal wurtzite. The average grain size and surface roughness increases with the increase of the Na/Zn ratio. The optical band gap of the thin films decreases from 3.26 to 3.12 eV by increasing the Na/Zn ratio from 0.0 to 0.10. Transmittance spectra were used to determine the optical constants of the thin films, and the effect of Na/Zn ratio on the optical constants was investigated. With the increase of Na/Zn ratio, the refractive index decreases and the extinction coefficient increases in the 380-700 nm spectral range.     

On the impact of non-sphericity and small-scale surface roughness on the optical properties of hematite aerosols

We perform a comparative modelling study to investigate how different morphological features influence the optical properties of hematite aerosols. We consider high-order Chebyshev particles as a proxy for aerosol with a small-scale surface roughness, and spheroids as a model for nonspherical aerosols with a smooth boundary surface. The modelling results are compared to those obtained for homogeneous spherical particles. It is found that for hematite particles with an absorption efficiency of order unity the difference in optical properties between spheres and spheroids disappears. For optically softer particles, such as ice particles at far-infrared wavelengths, this effect can be observed for absorption efficiencies lower than unity. The convergence of the optical properties of spheres and spheroids is caused by absorption and quenching of internal resonances inside the particles, which depend both on the imaginary part of the refractive index and on the size parameter, and to some extent on the real part of the refractive index. By contrast, small-scale surface roughness becomes the dominant morphological feature for large particles. This effect is likely to depend on the amplitude of the surface roughness, the relative significance of internal resonances, and possibly on the real part of the refractive index. The extinction cross section is rather insensitive to surface roughness, while the single-scattering albedo, asymmetry parameter, and the Mueller matrix are strongly influenced. Small-scale surface roughness reduces the backscattering cross section by up to a factor of 2-3 as compared to size-equivalent particles with a smooth boundary surface. This can have important implications for the interpretation of lidar backscattering observations.     

Modeling the radiative properties of nonspherical soil-derived mineral aerosols

Mineral dust aerosols have complex nonspherical shapes and varying composition. This study utilizes data on morphology (size and shape) and composition of dust particles to determine the extent to which the optical properties of real particles differ from those of spheres. A method for modeling the optical properties of complex particle mixtures is proposed. The method combines dust particle composition-shape-size (CSS) distributions reconstructed from the electron microscopy data, effective medium approximations and discrete dipole approximation. The method is used to compute optical characteristics of realistic dust mixtures representative of Saharan and Asian dust. We demonstrate that considered CSS distributions result in various differences in the extinction coefficient, single scattering albedo, asymmetry parameter and the scattering phase function relative to the volume-equivalent spheres and the mixtures of the randomly oriented oblate and prolate spheroids. Implications of these differences for radiation/climate modeling and remote sensing are discussed.     

Linear and nonlinear optical response of MgxZn1−xO: A density functional study

Total and partial density of states, frequency dependent complex refractive index including extinction coefficient, optical conductivity and transmission of Mg_xZn_1−xO (0≤x≤1) in rocksalt and wurtzite phases are calculated using full potential linearized augmented plane wave (FP-LAPW) method. The real part of refractive index decreases while the extinction coefficient, optical conductivity and transmission for rocksalt phase increases with the increase in Mg concentration. In wurtzite phase, ordinary and extraordinary indices decrease while extinction coefficient, optical conductivity and transmission increase in parallel as well as perpendicular to c-axis with the increase in the Mg concentration.