生物组织的δ-P1近似漫反射光学模型

本文研究了生物组织的改进的δ-P₁近似漫反射光学模型,推导了含有等效光源一阶矩的双点源近似空间分辨漫反射解R_δ－P1(ρ).研究表明,考虑等效光源一阶矩的光学模型,较好地描述了具有强的前向散射特性和较大吸收系数的生物组织散射特性;与漫射近似下的漫反射率R_SDA(ρ)相比,新的光学模型能较好地描述光源附近的漫辐射强度分布,并且由于解析表达式中含有散射相函数的二阶参量γ,这对 关键词： 组织光学 1近似')" href="#">δ-P₁近似 等效光源 微区漫反射     

Delta-P1近似漫反射光学模型的二阶参量灵敏度

基于Delta-P₁近似漫反射光学模型, 推导了双点源近似下空间分辨漫反射解对于Henyey-Greenstein散射相函数的二阶参量γ的灵敏度表达式, 研究了参量γ对漫反射分布的影响. 研究表明, 与漫射近似模型相比, Delta-P₁近似漫反射光学模型不仅含有散射相函数的二阶参量γ, 而且在弱吸收或强吸收的情况下, 参量γ对于光源附近(ρ<1.0 mm)的空间分辨漫反射都存在较大的影响(极值大于30%). 因此利用γ研究漫反射光分布对于获取组织光学信息具有重要的意义.     

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。     

基于P3近似的空间分辨漫反射研究

光源附近组织的空间分辨漫反射是近年来生物医学光子学领域的一个研究热点,其目的是发展一种能够测定活体生物组织光学参量的新技术。漫射近似理论研究光源附近组织的空间分辨漫反射具有很大局限性。P3近似理论考虑了相函数的三阶矩,能较准确地描述光源附近组织的光辐射分布。研究了基于P3近似的空间分辨漫反射,从输运理论的PN方程组出发,导出了P3近似方程组和P3近似的格林函数解;阐述了漫射近似与P1近似的关系,给出了外推边界条件下,准直光束近似后的P3近似漫反射率的完整表示,讨论了相函数二阶参量对P3近似漫反射的影响,并与漫射近似和蒙特卡罗模拟结果进行了比较,指出了P3近似的应用范围。     

空间分辨漫反射的高阶参量灵敏度

光源附近的空间分辨漫反射与散射介质的高阶光学参量有关.为了研究高阶参量对漫反射的影响，定义了二阶参量灵敏度和三阶参量灵敏度，它们表示了由于高阶参量变化导致漫反射变化的相对量.从P₃近似理论出发，推导了二阶参量灵敏度和三阶参量灵敏度的解析表示，并进行了数值分析和比较.研究表明，在大于一个输运平均自由程的非漫射近似区域，反射率随二阶光学参量增加而增加，其灵敏度随着空间变化，并在小于两个输运平均自由程内出现极大值；相比之下，三阶光学参量对漫反射率的影响可以忽略. 关键词： 漫反射 3近似')" href="#">P₃近似 灵敏度     

激光应用 激光医学

R318．51 2006065004生物组织中高阶光学参量对空间分辨漫反射的影响=In- fluenee of high-order parameters on tissue spatially re- solved reflectance[刊,中]/单筱莜(鞍山师范学院．辽宁,鞍山市(114005))．刘迎…//光电子·激光．—2006,17(6)．—767-771采用Monte Carlo方法研究了生物组织的二阶和三阶光学参量对空间分辨漫反射率R(ρ)的影响。当光源与探测器问距离ρ为几个输运平均自由程l_1时,漫射近似理论不再适用,R(ρ)与散射相函数的高阶Legendre矩有关。     

基于delta-P1近似模型的空间分辨漫反射一阶散射参量灵敏度研究

以delta-P1近似光学模型为基础, 推导了双点源近似下空间分辨漫反射一阶散射参量μ_s'灵敏度的解析式, 并进行了数值分析和比较. 研究表明, 与混合漫射近似模型和漫射近似模型相比, delta-P1 近似模型能更好地描述强散射较强吸收情况下近光源区域生物组织漫反射光子的分布, 且在有效反照率a'>0.83时, 获得最佳优化距离ρ_opt, ρ_opt 随μ_s' 的增大而减小, 且在距光源约2.7—4个输运平均自由程处μ_s'的变化对测量吸收的影响最小. 这项研究对于优化传感器几何结构以及生物组织光学参量的测量具有重要意义.     

小斜率近似在粗糙面激光散射BRDF计算中的应用

基于小斜率近似法建立了粗糙面激光散射双向反射分布函数的数学模型,采用该模型计算了粗糙度参量已知的合金铝样片的双向反射分布函数值,计算结果与实测结果吻合良好,验证了模型的正确性.研究了粗糙度参量和样片光学常量对双向反射分布函数的影响,结果表明,粗糙面激光散射的双向反射分布函数与表面高度起伏均方根、自相关长度及样片光学常量相关.当入射波长一定时,高度起伏均方根越大,或者自相关长度越小,粗糙面粗糙度越大,入射激光的漫反射特性越强,双向反射分布函数峰值越小且分布越分散;当粗糙度一定时,样片光学常量对双向反射分布函数影响较大,粗糙面对入射激光复折射率的虚部越大,样片双向反射分布函数的峰值越小,当粗糙度参量增大时,样片光学参量对双向反射分布函数的影响逐步减弱.     

生物组织的散射相函数及其二阶光学参量的性质

生物组织是一种复杂介质,在许多情况下仅仅用各向异性因子g来描述其散射特性是不够的。由于二阶参量γ是一个与相函数的二阶矩g2有关,并表示与一阶参量g1关系的量,因此用g和γ两个参量能更好地描述组织的光学性质。对几种目前用于描述人体组织的相函数及其二阶参量作了简要讨论,在此基础上研究了相函数的选取对测量参量γ的影响。研究表明γ是一个可测量的组织参量。研究工作对于建立含有相函数高阶矩的漫散射理论,对如何测量生物组织的高阶参量γ,并能够准确测量其它光学参量具有重要理论意义和实际府用价值。     

光源附近空间分辨漫反射的SP3研究

根据P₃近似对半无限生物组织的空间分辨漫反射理论,研究了强吸收条件下光源附近 光辐射分布的简化表达式SP₃函数.研究表明:组织吸收越强, SP₃函数越能准确描述光源附近空间 分辨漫反射;应用SP₃函数反演强吸收组织光学参数时,由不同起始距离的漫反射数据拟合得到的反演 结果曲线存在极值,极值附近对应的反演结果最接近实际组织光学参数.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.