New calibration method for the determination of the absolute density of CH radicals through laser-induced fluorescence

Laser-induced fluorescence (LIF) was applied at the B-X transition of the CH radical to measure the absolute densities of CH radicals in an electron-cyclotron resonance methane plasma. The absolute experimental uncertainty is only approximately 30% as a result of a new calibration procedure. The experimental setup was calibrated through the comparison of the LIF signal of N(2)(+) with that of CH. The absolute N(2)(+) density was derived from the spatially resolved N(2)(+) LIF signal and the line-averaged electron density as measured with microwave interferometry.     

两种方法测量大气气溶胶折射率的对比分析

针对气溶胶折射率在分析大气气溶胶光学特性中的重要性,介绍两种综合利用黑碳仪、浊度计、光学粒子计数器和微脉冲激光雷达测量大气气溶胶折射率的新方法。两种方法都是根据球形粒子的Mie散射理论计算大气气溶胶的折射率,使用以上两种方法对厦门地区气溶胶折射率进行了计算和对比分析,证明了它们的合理性,分析了它们的测量精度和误差来源。     

Dispersion measurement of inert gases and gas mixtures at 800 nm

Dispersion of femtosecond laser pulses propagating in Ar, He, Kr, N(2), Ne, Xe, and their mixtures is measured by spectrally and spatially resolved interferometry. By varying the gas pressure in a 4.5 m long tube between 0.05 mbar and ambient pressure, the first, second, and third order phase derivatives of broadband laser pulses are determined at 800 nm under standard conditions. The dispersion of gases and gas mixtures obeys the Lorentz-Lorenz formula with an accuracy of 0.7%. Based on the measured pressure dependent dispersion values in the near infrared and the refractive indices available from the literature for the ultraviolet and visible, a pressure dependent Sellmeier-type formula is fitted for each gas. These common form, two-term dispersion equations provide an accuracy between 4.1x10(-9) (Ne) and 4.3x10(-7) (Xe) for the refractive indices, from UV to near IR.     

Spatial distribution of synthetic fibers in concrete with X-ray computed tomography

The strength and toughness prediction models for fiber-reinforced concrete (FRC) typically assume the spatial distribution of fibers is uniform. However, non-uniform dispersion can greatly affect the FRC’s mechanical properties. Several techniques have been used in the past to quantify the distribution and orientation of steel fibers within concrete. For quantifying dispersion of synthetic fibers within concrete, a non-destructive technique using X-ray computed tomography (CT) combined with a post-processing image analysis is proposed. Due to X-ray attenuation similarities, the synthetic fibers were resolved from air voids by shape and size-based filters. The described approach to determine the actual fiber content within FRC samples was verified to be accurate. The method can be used to determine the individual fiber spatial distribution inside the concrete. As expected, the actual volume fraction of fibers in a fracture sample was correlated with the measured total fracture energy of the sample.     

Accelerator-based neutron tomography cooperating with X-ray radiography

Neutron resonance absorption spectroscopy (N-RAS) using a pulsed neutron source can be applied to time-of-flight (TOF) radiography, and the obtained parameters from the peak shape analysis can be reconstructed as the tomograms of nuclide distributions using computed tomography (CT). The problem is that the available spatial resolution is not sufficient for radiography imaging. In this study, we combined neutron and X-ray radiographies to improve the quantitative reconstruction of the neutron tomogram. The accelerator-based neutron source emits X-rays (or gamma-rays) at the same time the neutron pulse is emitted. We utilized the X-ray beam from the neutron source to obtain X-ray radiogram on the same beam line with neutron radiography and then reconstructed the neutron tomogram quantitatively with the help of a detailed sample internal structure obtained from the X-ray radiogram. We calculated the nuclide number density distribution tomogram using a statistical reconstruction procedure, which was easy to include in the structure model during the reconstruction. The obtained result of nuclide number density distribution showed good coincidence with the original object number density.     

Spectrally resolved white-light interferometry for measurement of ocular dispersion.

Spectrally resolved white-light interferometry was used to measure the wavelength dependence of refractive index (i.e., dispersion) for various ocular components. Verification of the technique's efficacy was substantiated by accurate measurement of the dispersive properties of water and fused silica, which have both been well-characterized in the past by single-wavelength measurement of the refractive index. The dispersion of bovine and rabbit aqueous and vitreous humors was measured from 400 to 1100 nm. In addition, the dispersion was measured from 400 to 700 nm for aqueous and vitreous humors extracted from goat and rhesus monkey eyes. An unsuccessful attempt was also made to use the technique for dispersion measurement of bovine cornea and lens. The principles of white-light interferometry, including image analysis, measurement accuracy, and limitations of the technique, are discussed. In addition, alternate techniques and previous measurements of ocular dispersion are reviewed.     

Effects of RF bias power on electron energy distribution function and plasma uniformity in inductively coupled argon plasma

Changes in the plasma non-uniformity and the electron energy distribution function (EEDF) by increasing RF bias power were observed in inductively coupled plasma using spatially resolved radial EEDF measurements. As the bias power was increased at a fixed ICP power at a low gas pressure, The EEDF was evolved from a bi-Maxwellian to a Maxwellian distribution. The plasma density was decreased in all radial positions and thus plasma non-uniformity was slightly changed. However, strongly improved plasma spatial non-uniformity was observed at a high gas pressure with a decrease in the center-plasma density and an increase in the radial edge-plasma density. This result could be understood by combined effects of the ion acceleration loss and the non-uniform power deposition due to the RF bias power.     

Spatial versus temporal phase shifting in electronic speckle-pattern interferometry: noise comparison in phase maps

Temporal and spatial phase shifting in electronic speckle-pattern interferometry are compared quantitatively with respect to the quality of the resultant deformation phase maps. On the basis of an analysis of the noise in sawtooth fringes a figure of merit is defined and measured for various in-plane and out-of-plane sensitive electronic speckle-pattern interferometry configurations. Varying quantities like the object-illuminating intensity, the beam ratio, the speckle size and shape, and the fringe density allows characteristic behaviors of both phase-shifting methods to be explored.     

Plasmonic focusing reduces ensemble linewidth of silver-coated gold nanorods

Silver coating gold nanorods reduces the ensemble plasmon line width by changing the relation connecting particle shape and plasmon resonance wavelength. This change, we term "plasmonic focusing", leads to less variation of resonance wavelengths for the same particle size distribution. We also find smaller single particle linewidth comparing resonances at the same wavelength but show that this does not contribute to the ensemble linewidth narrowing.     

Localized surface plasmon resonance spectroscopy of single silver triangular nanoprisms

The plasmonic properties of single silver triangular nanoprisms are investigated using dark-field optical microscopy and spectroscopy. Two distinct localized surface plasmon resonances (LSPR) are observed. These are assigned as in-plane dipolar and quadrupolar plasmon excitations using electrodynamic modeling based on the discrete dipole approximation (DDA). The dipole resonance is found to be very intense, and its peak wavelength is extremely sensitive to the height, edge length, and tip sharpness of the triangular nanoprism. In contrast, the intensity of the quadrupole resonance is much weaker relative to the dipole resonance in the single particle spectra than in the ensemble averaged spectrum. Several parameters relevant to the chemical sensing properties of these nanoprisms have been measured. The dependence of the dipole plasmon resonance on the refractive index of the external medium is found to be as high as 205 nm RIU(-1) and the plasmon line width as narrow as approximately 0.17 eV. These data lead to a sensing figure of merit (FOM), the slope of refractive index sensitivity in eV RIU(-1)/line width (eV), as high as 3.3. In addition, the LSPR shift response to alkanethiol chain length was found to be linear with a slope of 4.4 nm per CH2 unit. This is the highest short-range refractive index sensitivity yet measured for a nanoparticle.     

Distributed liquid level sensors using self-heated optical fibers for cryogenic liquid management

We present a continuous liquid level sensing system for both room temperature and cryogenic fluids with millimeter spatial resolution. Change of in-fiber Rayleigh backscattering signal from the distinct thermal response of the heated sensing fiber in liquid and in air were interrogated and spatially resolved using the optical frequency domain reflectometry. Both electrical and optical heating techniques were investigated for cryogenic liquid applications at 4?K, 77?K, and the room temperature. The successful combination of self-heated fiber and wavelength-swept Rayleigh scattering interferometry provides, for the first time to our best knowledge, a truly distributed fuel gauge with high spatial resolution for cryogenic fuel storage, transportation, and management on ground and in space.     

Three-dimensional shape measurement beyond the diffraction limit of lens using speckle interferometry

Speckle interferometry is generally known as a method for measuring the deformation of an object with rough surfaces. In this paper, a three-dimensional (3D) shape measurement method is proposed for superfine structures beyond the diffraction limit using the basic property of speckle interferometry. Since the differential coefficient distribution of the shape of such an object can be detected in speckle interferometry by imparting a known lateral shift to the measured object, the shape can be reconstructed by integrating the differential coefficient distribution. Based on experimental results obtained using diffraction gratings as measured objects, it is confirmed that the proposed method can measure 3D shapes that are beyond the diffraction limit of the lens.     

A new method to determine specific surface area and shape coefficient of a cohesionless granular medium

The specific surface area of soil grains (SSA) influences the physical and chemical properties of soil. Despite the widespread application of the SSA, it is often determined by analytical equations or estimated using empirical relationships and visual comparisons. On the other hand, little attention has been paid, especially to three-dimensional and precise measurements. In this study, the precise SSA and shape coefficient was measured in a group of aggregate with different sizes and shapes using a novel method. Geometrical properties such as volume and surface area were measured for each particle using X-ray micro-computed tomography (µCT) images and image processing. The particle shape coefficient was obtained from the specific surface area and effective diameter. Further, the particle shapes were measured in three distinct characteristics, sphericity, roundness, and roughness. Particle's roundness was measured by Wadell’s formula in the plan outline, which did not show an agreement with the shape coefficient. Nevertheless, as the particle sphericity decreases and roughness increases, the shape coefficient is increased. Hence, the shape coefficient of grains was classified based on the sphericity and the surface roughness. The measured SSA and shape coefficient, for 12 gradations with the three different particle size distribution and four different particle shapes, indicated good agreement with predictive analytical relations for rounded and crushed grains and more dissimilarity for flaky and elongated grains. This novel method can provide the quantitative/qualitative classification for non-spherical particles and also improve our understanding on the properties of granular media.     

Angular distribution of light scattered by single biological cells and oriented particle agglomerates

We used a flow cytometer together with an intensified CCD camera to record spatially resolved light scattering from micrometer-sized single particles and single oriented particle agglomerates. Experimental differential cross sections of an oriented dumbbell made from two identical polystyrene spheres were compared with theoretical values calculated within the discrete dipole approximation, and good agreement was achieved. Furthermore, characteristic two-dimensional patterns of the scattered-light intensity were recorded for single blood cells, yielding information on the cells' shape and volume. Besides flow cytometry, we observed and analyzed differential light scatter of particle clusters of known size, shape, and orientation located within an optical trap.     

Spatial and temporal observation of energy transfer processes in Pr-doped phosphate glasses

A spatially resolved microluminescence technique was used to measure the spatial distribution of emitted light and photon propagation into two different Pr³⁺ doped phosphate glasses. The photon diffusion length for specific wavelengths was measured. It was found that excited state re-absorption plays a crucial role in the propagation. Our results suggest that this microluminescence technique can be applied in the investigation of energy transfer processes in rare-earth doped systems.     

亚微米级扁椭球颗粒群的散射特性

采用T矩阵方法计算亚微米级扁椭球随机取向分布颗粒群的散射特性,研究消光截面、散射截面、吸光截面、单散射反照率、非对称因子以及散射矩阵元素与颗粒的大小、折射率、长短轴比之间的关系。结果表明,随颗粒粒径增大,消光截面、散射截面、吸光截面、非对称因子都单调增加,散射相函数F11的角分布曲线特征可以区分颗粒的大小;颗粒越偏离球形,颗粒对入射光的衰减效率越低,后向散射光强越强,在轴比不大时,前向50°内的F22/F11值可以区分颗粒的形状;折射率变化主要是对后向散射光的分布产生影响,实部、虚部的变化可分别通过F34/F11的角分布曲线、F12/F11的第一个峰值来体现。     

Investigation of spatially resolved light absorption in a spark-ignition engine fueled with propane/air

UV absorption in the combustion phase of spark-ignition engines strongly influences laser-induced-fluorescence measurements and flame-emission techniques because of the attenuation of a laser and/or signal light. This absorption was assessed with spatial, spectral, and temporal resolutions in an optically accessible research engine. Absorption was measured along a line for different crank-angle positions throughout the combustion phase of the engine by use of spectrally resolved transmittance measurements of both broadband illumination from a deuterium lamp and emission of laser-excited hot oxygen. Evaluating the spatial patterns of absorptivity revealed that no increased absorption can be attributed to the flame-front region and that homogeneous absorption cross sections for the whole burned-gas region can be assumed. The temporal change of absorption was shown to depend on the pressure effect with only negligible changes in absorption cross sections. Results obtained from the absorption measurements are applied for spatially resolved corrections of two-dimensional laser-induced-fluorescence measurements of NO concentration fields obtained under different operating conditions.     

Parallel scan spectral surface plasmon resonance imaging

We describe a parallel scan spectral surface plasmon resonance (SPR) imaging technique. We demonstrate experimentally, with a line-shaped light illumination, that an image acquired with an area CCD detector provides both SPR wavelength information and one-dimensional spatial distribution. Thus two-dimensional distribution of the refractive index of the entire sensing plane can be obtained with a one-dimensional optical line parallel scan. The technique offers advantages of both high sensitivity and high throughput, and could have potential applications in biochips analysis.     

High-resolution tomographic imaging of a human cerebellum: comparison of absorption and grating-based phase contrast

Human brain tissue belongs to the most impressive and delicate three-dimensional structures in nature. Its outstanding functional importance in the organism implies a strong need for brain imaging modalities. Although magnetic resonance imaging provides deep insights, its spatial resolution is insufficient to study the structure on the level of individual cells. Therefore, our knowledge of brain microstructure currently relies on two-dimensional techniques, optical and electron microscopy, which generally require severe preparation procedures including sectioning and staining. X-ray absorption microtomography yields the necessary spatial resolution, but since the composition of the different types of brain tissue is similar, the images show only marginal contrast. An alternative to absorption could be X-ray phase contrast, which is known for much better discrimination of soft tissues but requires more intricate machinery. In the present communication, we report an evaluation of the recently developed X-ray grating interferometry technique, applied to obtain phase-contrast as well as absorption-contrast synchrotron radiation-based microtomography of human cerebellum. The results are quantitatively compared with synchrotron radiation-based microtomography in optimized absorption-contrast mode. It is demonstrated that grating interferometry allows identifying besides the blood vessels, the stratum moleculare, the stratum granulosum and the white matter. Along the periphery of the stratum granulosum, we have detected microstructures about 40 µm in diameter, which we associate with the Purkinje cells because of their location, size, shape and density. The detection of individual Purkinje cells without the application of any stain or contrast agent is unique in the field of computed tomography and sets new standards in non-destructive three-dimensional imaging.     

Simultaneous extraction of optical transport parameters and intrinsic fluorescence of tissue mimicking model media using a spatially resolved fluorescence technique

We present a method based on spatially resolved fluorescence measurement for the simultaneous estimation of optical transport parameters, namely, the reduced scattering coefficient (micro s'), the absorption coefficient (micro a), and the intrinsic fluorescence spectra from turbid media. The accuracy of this approach was tested by conducting studies on a series of tissue-simulating phantoms with known optical transport properties. The estimated relative error in the values for micro s' and micro a using this technique was found to be < or =10%. Furthermore, the line shape and intensity of the intrinsic fluorescence recovered by using this approach were observed to be free from the distorting effects of the wavelength-dependent absorption and scattering properties of the medium, and they were in excellent agreement with the directly measured intrinsic fluorescence spectra of the fluorophores.