高散射媒质中的光程可分割动态光散射研究

为研究散射光强度随光子在散射媒质中散射光程的变化,基于单散射理论与扩散波光谱理论,采用了低相干动态光散射装置对不同粒径大小的聚苯乙烯悬浮液进行研究。将测量得到的背散射光光场强度谱的线宽与相应的理论计算结果相比较发现,在短光程区域,考虑容器壁附近拖曳效应的影响后,对于不同粒径的颗粒,光程为约5倍粒子平均自由程的区域可看成为单散射区域;对于光程大于225 m的区域可看成为扩散光波区域。实验结果表明低相干动态光散射法可实现高散射媒质从单散射区域到低次散射再到扩散区域的全光程的可分割的光场强度谱测量。     

Doppler-angle measurement in highly scattering media

We describe a dual-channel optical low-coherence reflectometer for accurate measurement of Doppler angles in highly scattering media. Accurate fluid-flow velocity estimation requires measurement of the Doppler shift and angle. Estimated values of the Doppler angle and average fluid-flow velocity from experimental data are in good agreement with preset values.     

Time-resolved optical backscattering model in highly scattering media

A time-resolved backscattering model, which combines a single large-angle scattering with multiple small-angle scatterings, is used to produce a scattered-light profile about a medium. Inhomogeneity of the medium is included in the model. Some multidimensional integrals can be evaluated analytically.     

Temperature-corrected spectroscopic evaluation method for gas concentration monitoring

Combustion exhaust monitoring was simulated by measurement on a sulfur dioxide flow at different temperatures using broadband absorption spectroscopy and electrochemical analysis. A linear relationship with varying rates of slope for different temperatures was found between the gas concentrations obtained using the two methods, attributed to the influence of gas volume increase and absorption line broadening. By utilizing the differential absorption at an on/off pair combined with an experimentally determined temperature correction coefficient, the sulfur dioxide concentration was evaluated with the spectroscopic method yielding a measurement precision of 4%. PACS 42.68.Ca; 33.20.Lg     

Low-coherence enhanced backscattering from highly forward scattering media

We present a theoretical basis for calculation of the angular profile of the coherent backscattering intensity under low spatial coherence illumination. We take into account two contributions to the intensity, namely, the diffusion contribution and the contribution from the waves that experience the small-angle multiple scattering before and after single deflection in the backward direction. The latter contribution describes transport of light at subdiffusion length scales and is responsible for the wings of the backscattering angular profile. Our results are in good agreement with data of Monte-Carlo simulations and experiment.     

Generation of Lommel beams through highly scattering media

Lommel beams have been potential candidates for optical communication and optical manipulation, due to their adjustable symmetry of transverse intensity distribution and continuously variable orbital angular momentum. However, the wavefront of the Lommel beam is scrambled when it transmits through highly scattering media. Here, we explore the construction of Lommel beams through highly scattering media with a transmission matrix-based point spread function engineering method. Experimentally, var...     

A spectroscopic method for determining thickness of quartz wave plate

A spectroscopic method to determine thickness of quartz wave plate is presented. The method is based on chromatic polarization interferometry. With the polarization-resolved transmission spectrum (PRTS)curve, the phase retardation of quartz wave plate can be determined at a wide spectral range from 200 to2000 nm obviously. Through accurate judgment of extreme points of PRTS curve at long-wave band, the physical thickness of quartz wave plates can be obtained exactly. We give a measuring example and the error analysis. It is found that the measuring precision of thickness is mainly determined by the spectral resolution of spectrometer.     

Spectral measurements of the emission from highly scattering gain media

The spectral properties of the emission of a colloidal suspension of titanium dioxide particles in Rhodamine 640 perchlorate were studied systematically. The particle density rho, the dye concentration c, and the energy of the pump pulse were varied over several orders of magnitude; the dependence of the spectra on these three parameters is discussed. We discovered a strong correlation between the particle density and the dye concentration. The amplification by stimulated emission was found to be strongest when the absorption length l(a) and the mean-free-path length l(*) had approximately the same magnitude. The respective l(*) values were determined by a pulsed transmission experiment.     

Asymptotic method for determining the amplitude for three-particle breakup: Neutron-deuteron scattering

The process of neutron-deuteron scattering at energies above the deuteron-breakup threshold is described within the three-body formalism of Faddeev equations. Use is made of the method of solving Faddeev equations in configuration space on the basis of expanding wave-function components in the asymptotic region in bases of eigenfunctions of specially chosen operators. Asymptotically, wave-function components are represented in the form of an expansion in an orthonormalized basis of functions depending on the hyperangle. This basis makes it possible to orthogonalize the contributions of elastic-scattering and breakup channels. The proposed method permits determining scattering and breakup parameters from the asymptotic representation of the wave function without reconstructing it over the entire configuration space. The scattering and breakup amplitudes for states of total spin S = 1/2 and 3/2 were obtained for the s-wave Faddeev equation.     

A spectroscopic method of determining the isotopic composition of magnesium

The composition is determined from the isotopic shift of the Mgl 880.68 nm line. The coefficient of variation for magnesium metal is 1.8%, but 4% for magnesium oxide. Several spectroscopic analyses can be performed in the time needed for one mass-spectrometer analysis, which reduces the error of analysis by a factor two or three.We are indebted to Professor A.N. Zaidel for valuable advice and to N. A. Novozhilova for assistance with the measurements.     

Combined taper-and-cylinder optical fiber probes for highly sensitive surface-enhanced Raman scattering

A combined taper-and-cylinder optical fiber fabricated by simple tube-etching and modified with silver nanoparticles is developed for surface-enhanced Raman scattering (SERS) sensing. It has the advantages of high light transmission efficiency and large interaction areas for light and silver nanoparticles. The detection of rhodamine 6G in remote mode indicates that the sensitivity could realize 10^?13 M. The fiber SERS probe with high flexibility and sensitivity shows great potential for molecule detection in various sensing applications.     

Coherence gating in optical heterodyne detection measurements of scattering and absorption in highly scattering media

Laser-Induced Fluorescence (LIF) from the S₁ state of acetone and 3-pentanone was studied as a function of temperature and pressure using excitation at 248 nm. Additionally, LIF of 3-pentanone was investigated using 277 and 312 nm excitation. Added gases were synthetic air, O₂, and N₂ respectively, in the range 0–50 bar. At 383 K and for excitation at 248 nm, all the chosen collision partners gave an initial enhancement in fluorescence intensity with added gas pressure. Thereafter, the signal intensity remained constant for N₂ but decreased markedly for O₂. For synthetic air, only a small decrease occurred beyond 25 bar. At longer excitation wavelengths (277 and 312 nm), the corresponding initial rise in signal with synthetic air pressure was less than that for 248 nm. The temperature dependence of the fluorescence intensity was determined in the range 383–640 K at a constant pressure of 1 bar synthetic air. For 248 nm excitation, a marked fall in the fluorescence signal was observed, whereas for 277 nm excitation the corresponding decrease was only half as strong. By contrast, exciting 3-pentanone at 312 nm, the signal intensity increased markedly in the same temperature range. These results are consistent with the observation of a red shift of the absorption spectra (9 nm) over this temperature range. Essentially, the same temperature dependence was obtained at 10 and 20 bar pressure of synthetic air. It is demonstrated that temperatures can be determined from the relative fluorescence intensities following excitation of 3-pentanone at 248 and 312 nm, respectively. This new approach could be of interest as a non-intrusive thermometry method, e.g., for the compression phase in combustion engines.     

Coherent backscattering enhancement in highly anisotropically scattering media: Numerical solution

The problem of coherent backscattering enhancement in media with highly anisotropic scattering is considered within the scalar wave theory. A stable computational algorithm, suitable for the media of finite thickness, is formulated. Numerical simulations are performed, and the results are presented and discussed.     

A field expansions method for scattering by periodic multilayered media

The interaction of acoustic and electromagnetic waves with periodic structures plays an important role in a wide range of problems of scientific and technological interest. This contribution focuses upon the robust and high-order numerical simulation of a model for the interaction of pressure waves generated within the earth incident upon layers of sediment near the surface. Herein described is a boundary perturbation method for the numerical simulation of scattering returns from irregularly shaped periodic layered media. The method requires only the discretization of the layer interfaces (so that the number of unknowns is an order of magnitude smaller than finite difference and finite element simulations), while it avoids not only the need for specialized quadrature rules but also the dense linear systems characteristic of boundary integral/element methods. The approach is a generalization to multiple layers of Bruno and Reitich's "Method of Field Expansions" for dielectric structures with two layers. By simply considering the entire structure simultaneously, rather than solving in individual layers separately, the full field can be recovered in time proportional to the number of interfaces. As with the original field expansions method, this approach is extremely efficient and spectrally accurate.     

An interferometric method for determining the mean refractive indices of highly birefringent fibres

An interferometric method with its mathematical derivation is suggested to determine the mean refractive indices and birefringence of highly birefringent fibres using multiple-beam Fizeau fringes in transmission. The application of this method depends on measuring the cross-sectional area of the fibre and the area enclosed under the fringe shift. It is very difficult to measure the area enclosed under the fringe shift in case of highly birefringent fibres, as these fibres have a relatively large optical path difference and a bad connection with the surrounding medium fringe. This difficulty is solved using the suggested method. Poly(aryel ether ether ketone) (PEEK) and poly(ethylene 2,6-naphthalene-dicarboxylate) (PEN) were used as applied examples of highly birefringent fibres for the suggested method. The refractive indices and birefringence of polypropylene fibre with draw ratio 4 are determined using the suggested and conventional methods. The results of the two methods are compared and it is found to be in agreement with the previously published data. The diffraction of He–Ne laser beam was used to determine the mean value of cross-sectional areas of fibres. Microinterferograms and tables are given for illustrations.     

Optical Doppler tomographic imaging of fluid flow velocity in highly scattering media

An optical Doppler tomography (ODT) system that permits imaging of fluid flow velocity in highly scattering media is described. ODT combines Doppler velocimetry with the high spatial resolution of low-coherence optical interferometry to measure fluid flow velocity at discrete spatial locations. Tomographic imaging of particle flow velocity within a circular conduit submerged 1 mm below the surface in a highly scattering phantom of Intralipid is demonstrated.     

Discrete ordinates method for propagation of light in highly scattering vascular tissues

This work considers the propagation of light in a semitransparent layer of vascular tissue, submitted to radiative boundary conditions. The solution procedure must provide accurate light distribution in the layer, so a discrete ordinates method based on the exact transport theory is carried out. An advantage of this method is its ability to account easily for various boundary conditions as well as optical heterogeneity. The influences of anisotropic scattering, optical discontinuity, optical parameters of tissue and refractive index on radiant fluence rate are investigated carefully. It is shown that reflections tend to produce more uniform profiles within the tissue.