Consistent determination of photoluminescence quantum efficiency for phosphors in the form of solution, plate, thin film, and powder

We have developed an improved method for easily determining the photoluminescence quantum efficiencies of transparent materials, such as solutions, glass plates, and thin films on a substrate, having various absorbances from ca. 0.05 to 1.0 at the excitation wavelength when reabsorption is negligible. The estimated accuracy for emitting semiconductor nanocrystals is ±5% for solutions. The efficiencies of non-transparent material, such as powder, together with the above-mentioned transparent materials were measured using the traditional integrating sphere method. Comparison of the two values showed that the traditional integrating sphere method usually underestimates the efficiency of powder samples ca. 10-20% depending on the optical density of the powder. This is because the emissions from more than ca. 0.2 mm deep do not leave the powder sample due to internal scattering. We also developed a method to overcome this problem.     

噻酮对离体乳猪皮肤光透明效果影响的实验研究

研究一种新型促渗剂——噻酮对皮肤组织光透明效果的影响。分别用单纯聚乙二醇400(PEG400)溶液以及PEG400与噻酮的混合溶液作用于含角质层及去角质层的离体乳猪皮肤,利用积分球系统动态检测样品对632．8 nm光的透射率变化,并对样品拍照获得直观图。结果表明:混合溶液作用于两种皮肤模型后,其光透明性均有不同程度的增加,即衰减系数降低;比较去角质层皮肤与含角质层皮肤的衰减系数的变化,前者比后者大19倍;单纯的PEG400仅对去角质皮肤有一定的光透明效果,并且所导致的皮肤衰减系数的降低仅为混合液作用后的2/3。因此,噻酮作为良好的促渗剂能与PEG400产生协同效应,有效提高皮肤光透明效果。     

基于截断奇异值分解的三维火焰温度场重建研究

利用CCD摄像机得到的火焰辐射能图像进行炉膛三维火焰温度场重建，但温度重建矩阵方程是一个不适定方程组，从而重建问题是一个不适定问题.应用截断奇异值分解(truncated singular value decomposition，TSVD)的正则化方法对该不适定方程组进行求解，并且采用了L曲线法对正则化参数进行选取.结合重建算例，采用奇异值分解(singular value decomposition，SVD)与离散Picard条件对这个不适定问题进行了分析.重建结果表明，在不同的模拟测量误差下，TSVD能够成功得到合理的解，重建温度场较好的再现了原始假设温度场的特征.     

Near-field optical microscopy using an integrating sphere

A scanning near-field optical microscope using an integrating sphere is demonstrated. The images from a usual near-field optical microscope often include contrasts caused by the sample structure because the reflection and transmission angles of signal waves depend on the size and shape of the sample. The observation angle dependency of signals can be avoided by using an integrating sphere. Background signals resulting from using the sphere can be reduced by using lock-in detection synchronously with modulation of tip–sample distance. The whole detection system is possibly useful for observing the distribution of the refractive index and/or the absorption coefficient. Received: 27 October 2000 / Final version: 29 August 2001 / Published online: 7 November 2001     

The flow of a model suspension fluid past a sphere

The paper is concerned with the flow of a dilute suspension of monosized spheroids past a sphere placed at the centerline of a cylindrical tube. The suspension is modeled by the transversely isotropic fluid model and the numerical solution is obtained by a time-dependent boundary element method. No steady-state solution to the problem was found. However, the amplitude of the long-time oscillations in the drag force on the sphere is only about 1% of its mean value at a solid volume concentration of 0.01 and an aspect ratio of 10 for the spheroids. The initial orientation of the microstructure has a small effect on the drag force: it can give rise to a ±1 % variation in the drag force at large time.     

Multi-wavelength holography in Bi12TiO20 crystals: Applications in refractometry

We present a recent development in holography with multimode, large free-spectral range (FSR) diode lasers in photorefractive sillenite crystals. A novel refractometry method based on this type of holographic recording in Bi₁₂TiO₂₀ (BTO) crystals is proposed. The holographic image of a prism-shaped transparent sample appears covered of interference fringes, and as the sample is properly translated, the fringes run along the holographic image. An expression providing the refractive index of the medium as a function of the sample displacement and the correspondent number of running fringes was derived. The refractive indexes of optical (BK7) glass, ethanol, hexan, cumene and aqueous solution of NaCl with different concentrations were measured in order to test the method. The obtained results are in good agreement with the ones reported in literature or measured by us using a commercial Abbe refractometre.     

Absolute Measurements of Photoluminescence Quantum Yields of Solutions Using an Integrating Sphere

We demonstrate that absolute measurements of the photoluminescence quantum yield of solutions can be made using an integrating sphere and a conventional fluorimeter. With this method the need for measurements against a luminescence standard is overcome. The sphere is mounted inside a commercial fluorimeter, which gives flexibility in excitation and emission wavelength ranges. A number of compounds have been investigated and the results are compared to literature values and data obtained using a comparative method.     

Finite element approximation of the Fokker-Planck equation for diffuse optical tomography

In diffuse optical tomography, light transport theory is used to describe photon propagation inside turbid medium. A commonly used simplification for the radiative transport equation is the diffusion approximation due to computational feasibility. However, it is known that the diffusion approximation is not valid close to the sources and boundary and in low-scattering regions. Fokker-Planck equation describes light propagation when scattering is forward-peaked. In this article a numerical solution of the Fokker-Planck equation using finite element method is developed. Approach is validated against Monte Carlo simulation and compared with the diffusion approximation. The results show that the Fokker-Planck equation gives equal or better results than the diffusion approximation on the boundary of a homogeneous medium and in turbid medium containing a low-scattering region when scattering is forward-peaked.     

积分球非中性对出射光谱的影响

从积分球非中性的角度出发,研究了光(辐射)经过积分球后的光谱性质变化.根据积分球理论公式,推导了积分球光谱透过率的非中性与内壁涂层光谱反射比非中性的关系,证明积分球非中性通常大于内壁涂层非中性|且内壁涂层非中性一定时,涂层反射比越高,积分球非中性越大.然后分别以A光源和氙灯作为入射光源,测量了硫酸钡和聚四氟乙烯两种典型涂层的积分球出射光的光谱分布、色坐标和色温.结果表明,两种积分球的非中性对出射光谱的影响特征相同,表现在色度上是色坐标(x,y)增大,色温降低.其中聚四氟乙烯积分球非中性较小,其出射光色温在A光源、氙灯作为入射光源时分别降低约20 K和70 K|而硫酸钡积分球的出射光色温则分别降低约300 K和1 000 K,非中性影响明显.     

Integrating sphere effective optical path length calibration by gas absorption spectroscopy

A method of integrating sphere effective optical path length (EOPL) evaluation using tunable diode laser absorption spectroscopy for gas detection was demonstrated. Oxygen was used as a sample gas for an 8.38 cm diameter integrating sphere calibration; 393.7 ± 1.3 cm EOPL was obtained from the wavelength modulation spectroscopy with second harmonic calibration by measuring oxygen P11 line at 764 nm, which is in agreement with that of 393 cm by using direct absorption spectroscopy calibration. The EOPL calibration accuracy of this method can reach 0.33 %. It has been justified that the EOPL of an integrating sphere is independent of the incident light intensity.     

Initial-value problem for plasma oscillations in a uniform magnetic field

The solution is given of the initial-value problem for the nonrelativistic linearised Vlasov-Maxwell equations describing longitudinal and transverse plasma oscillations in an external uniform magnetic field. The problem is solved for all directions of propagation except normal to the external magnetic field, and the equilibrium distribution is not assumed isotropic. The method of solution is an extension of Van Kampen's eigenfunction expansion technique, already developed considerably by Zelazny and McCure, in which the problem is reduced to the solution of a system of singular integral equations.     

小波在求解黑体辐射反问题中的应用

针对黑体辐射反问题,提出将其离散为线性不适定问题,利用小波变换方法进行数值求解.将小波变换和正则化方法相结合,利用小波函数的紧支撑性,将原不适定问题转化为粗子空间上的适定问题.数值模拟结果表明方法可行,重构区域温度分布有效.     

Remote sample characterization based on fluorescence monitoring

The possibilities and limitations of remote sample characterization using induced fluorescence are discussed. General equations for remote sensing of fluorescence are presented and discussed. The implications of different elements of a system for remote fluorescence sensing on different parameters of the equations are treated. Background light influence and signal processing are considered. Pulsed lasers, flashlamps and cw lamps as excitation sources are compared when matched to the proper detection scheme employing boxcar integration or lock-in detection. Model experiments have been performed to demonstrate different measurement strategies. Examples from remote oil-slick characterization are chosen as illustrations.     

基于积分球反射计的红外光谱发射率测量系统校正方法

针对非理想参考反射标准对光谱发射率测量结果的影响,基于积分球反射计的红外发射率测量系统原理,提出了一种适用于反射法光谱发射率测量系统的校正方法。通过参考反射标准样光谱反射率的数据拟合,得到反射率的曲线方程,计算反射测量系统的校正系数,校正参考标准样的输出电压,推导出光谱反射率为1的参考标准样输出电压曲线,消除了非理想参考标准造成的系统误差。应用该修正方法对基于积分球反射计的太阳能选择吸收涂层光谱发射率测量系统进行了校正,将校正后的光谱发射率测量结果与能量比较法的测量结果进行对比,验证了校正方法的可行性,有效性,提高了光谱发射率测量的准确度。     

Equations governing the oscillations of a self-gravitating elastic sphere under the influence of gravitational waves

We consider the influence of a plane gravitational wave on the following Newtonian system: a self-gravitating elastic sphere without rotation. We determine the equation governing the elastic oscillations within the framework of the general relativity. We include dissipative processes by using a simple relativistic model of viscoelasticity. If the wavelength is much larger than the dimension of the elastic sphere, we transform these equations into the form derived by Ashby and Dreitlein previously. We also determine the equations governing the elastic oscillations within the framework of the Brans-Dicke scalar-tensor theory of gravitation.     

离体正常乳腺组织350～850 nm波段光谱特性

采用带有积分球附件的紫外/可见/近红外分光光度计测量了离体正常乳腺组织在350～850 nm光谱范围的反射率和透射率,运用反向倍加法得到了离体正常乳腺组织在相应光谱范围的光学参数,分析了正常乳腺组织的光学穿透深度随波长的变化情况。实验结果表明：350～850 nm波段正常乳腺组织的约化散射系数μ′_s大于吸收系数μ_a。μ′_s随着波长的增加而减小,即从350 nm波长值为9.731 mm-1～850 nm波长值为1.476 mm-1。μ_a从350 nm波长值为0.798 mm-1～850 nm波长值为0.102 mm-1,410 nm波长处存在一个吸收峰,其值为0.506 mm-1。光学穿透深度随着波长的增加而增大,从350 nm波长值为0.199 mm-1～850 nm波长值为1.439 mm。基于反向倍加法计算获得乳腺组织的光学参数,采用Monte Carlo模拟得到其相应光谱范围的反射率和透射率,并与实际测量值进行比较,二者的一致性较好。实验结果为乳腺组织的光活检及其光学治疗提供重要参考。     

Image reconstruction in diffuse optical tomography using the coupled radiative transport-diffusion model

The coupled radiative transport-diffusion model can be used as light transport model in situations in which the diffusion equation is not a valid approximation everywhere in the domain. In the coupled model, light propagation is modelled with the radiative transport equation in sub-domains in which the approximations of the diffusion equation are not valid, such as within low-scattering regions, and the diffusion approximation is used elsewhere in the domain. In this paper, an image reconstruction method for diffuse optical tomography based on using the coupled radiative transport-diffusion model is developed. In the approach, absorption and scattering distributions are estimated by minimising a regularised least-squares error between the measured data and solution of the coupled model. The approach is tested with simulations. Reconstructions from different cases including domains with low-scattering regions are shown. The results show that the coupled radiative transport-diffusion model can be utilised in image reconstruction problem of diffuse optical tomography and that it produces as good quality reconstructions as the full radiative transport equation also in the presence of low-scattering regions.     

An efficient method for model refinement in diffuse optical tomography

Diffuse optical tomography (DOT) is a non-linear, ill-posed, boundary value and optimization problem which necessitates regularization. Also, Bayesian methods are suitable owing to measurements data are sparse and correlated. In such problems which are solved with iterative methods, for stabilization and better convergence, the solution space must be small. These constraints subject to extensive and overdetermined system of equations which model retrieving criteria specially total least squares (TLS) must to refine model error. Using TLS is limited to linear systems which is not achievable when applying traditional Bayesian methods. This paper presents an efficient method for model refinement using regularized total least squares (RTLS) for treating on linearized DOT problem, having maximum a posteriori (MAP) estimator and Tikhonov regulator. This is done with combination Bayesian and regularization tools as preconditioner matrices, applying them to equations and then using RTLS to the resulting linear equations. The preconditioning matrixes are guided by patient specific information as well as a priori knowledge gained from the training set. Simulation results illustrate that proposed method improves the image reconstruction performance and localize the abnormally well.     

Roughness and correlation-length determination of rough-surface objects using the speckle contrast

A method using the speckle contrast for the determination of both the roughness and the correlation length of surface-height variations of a rough-surface object is proposed on the basis of the statistical properties of the Gaussian speckle field in the image region. The expression for the speckle contrast is first theoretically derived in the optical imaging system as a function of the defocus distance and the surface parameters of the object. By solving the equations expressing the speckle contrasts at the image and defocus planes, a unique solution is found to exist for the roughness and the correlation length. In particular, a useful approximate relation that the roughness depends only on the contrast ratio is derived for relatively small values of the roughness. The experiments were performed to confirm the validity of the proposed method. The present method has an advantage of the simplicity in a measuring procedure where the contrasts at only the two points are required to determine the surface parameters.     

A simple method to simulate diffraction and speckle patterns with a PC

A simple, intuitive and pedagogical method is proposed in order to simulate the phenomenon of light diffraction in simple cases. A diffracting plane obstacle is simulated by means of a model with a variable transmittance from one point to another. A numerical matrix is built with transmittance values at those points taken as samples. The matrix is handled with the Matlab program, and the Fraunhofer approximation is used. The method is applied to variable module and constant phase transmittance obstacles in single slit, double slit, square window and round window cases. The method is also applied to an obstacle with a constant reflectance module and random variable phase with Gaussian statistics, which gives rise to speckle phenomenon.