Nd：YAG单晶光纤光学特性研究

本文测量了用激光加热基座法拉制的Nd:YAG单晶光纤(具有块状晶体)的吸收谱线,荧光谱线等光谱学特性.根据测得的散射特性分析了用该法拉制的单晶光纤的生长缺陷和直径波动及其与单晶光纤质量的关系.     

一种血流变参数在体实时探测方法

介绍了一种新的在体实时监测血流变参数的光学方法——光散射法。设计了一种实用的同轴多光纤探针装置。在装置中间,其中一根光纤用于传输入射激光,周围多根光纤与中心光纤等间隔,用于接收血液中的散射光。用扫描法布里-珀罗干涉仪产生散射光谱。结果表明,用该装置测得了含成分的液体、实血和不同血液成分的光散射光谱。     

蓝宝石光纤及其高温传感器

单晶蓝宝石光纤具有热稳定性好、机械性能强、化学性能稳定等优点,在高温、高压等恶劣环境中的应用受到广泛关注.介绍了单晶蓝宝石光纤的制备方法、基本特性及高温传输特性.重点讨论了目前基于单晶蓝宝石光纤制备的高温传感器件,包括法布里-珀罗干涉仪、布拉格光栅、以及迈克尔逊干涉仪,并分析了这些传感器的制备方法和工作原理.最后针对单晶蓝宝石光纤与传统单模光纤难兼容的问题,介绍了蓝宝石衍生光纤的制备及其传感器的最新进展,并展望了未来蓝宝石光纤的发展方向.     

采用解析法对Nd:YAG单晶光纤的温度场研究

采用解析法对Nd:YAG单晶光纤激光器热效应相关的光纤温度场分布进行研究。建立了Nd:YAG单晶光纤热模型,在单晶光纤所满足的边界条件下通过解析求解热传导方程,得到在高功率808 nm泵浦光抽运下产生946 nm激光的单晶光纤温度场分布,并与传统Nd∶YAG激光晶体的温度场进行比较,然后分别与同泵浦条件下的有限元数值方法的分析结果进行研究对比,最后分析泵浦光参数、单晶光纤参数等对温度场的影响。结果表明,功率为86 W的泵浦光入射至单晶光纤端面的最高温升仅为30.98℃,明显优于同泵浦条件下传统Nd∶YAG晶体的端面温升结果94.37℃,与有限元数值法得到的Nd:YAG单晶光纤19℃温升结果相比,该解析法结果更接近于实验的测量值31℃,能够更精确描述晶体光纤温度场。本文可对单晶光纤激光器热效应的精确研究提供一定参考,进而有利于提高单晶光纤激光器的性能。     

LED白光源用Pr3+,Ce3+:YAG光纤制备与特性

采用激光加热基座法制备LED白光源用Pr3+,Ce3+:YAG单晶光纤荧光材料,对所制备材料的荧光光学特性进行了实验分析结果表明,在Pr3+和Ce3+共掺发光过程中,Pr3+离子的发光可以通过Ce3+敏化作用使得其610 nm谱线荧光强度得到有效增强|利用所制备Pr3+,Ce3+:YAG单晶光纤荧光材料与蓝色LED合成产生高效LED光纤白光源,光源的色坐标为(x＝0.322,y＝0.335),显色指数84.3,表明光源品质良好,有望用于未来高效大功率光纤白光源.     

LED白光源用Pr~(3+),Ce~(3+):YAG光纤制备与特性

采用激光加热基座法制备LED白光源用Pr3+,Ce3+:YAG单晶光纤荧光材料,对所制备材料的荧光光学特性进行了实验分析结果表明,在Pr3+和Ce3+共掺发光过程中,Pr3+离子的发光可以通过Ce3+敏化作用使得其610 nm谱线荧光强度得到有效增强;利用所制备Pr3+,Ce3+:YAG单晶光纤荧光材料与蓝色LED合成产生高效LED光纤白光源,光源的色坐标为(x＝0.322,y＝0.335),显色指数84.3,表明光源品质良好,有望用于未来高效大功率光纤白光源.     

从室温到1800℃全程测温的蓝宝石单晶光纤温度传感器

表述了从室温到１８００℃测温范围的全程测温的蓝宝石单晶光纤温度传感器。该光纤传感器综合了光纤辐射测温技术和光纤荧光测温技术的特点,利用特殊生长的端部Ｃｒ＾３＋离子掺杂的蓝宝石单 光纤,使两者有机地结合实现用单一光纤传感头达到大范围的温度测量,介绍了端部掺杂的蓝宝石单晶光纤的生长方法,分析了它的荧光温度特性、光纤传感头上荧光信号与热辐射信号的相互干扰以及光纤温度传感器的系统结构和工作原理,给出了实验     

均匀折射率包层铌酸锂单晶光纤远离截止区的模特性讨论

给出了具有均匀折射率包层铌酸锂单晶光纤的场强颁上和本征值方程，分析了远离截止区的模特性。     

激光等离子体光谱测量影响因素分析

建立了一套激光等离子体光谱测量实验装置,以Nd:YAG调Q固体激光器(单脉冲平均能量38 mJ)为激发光源,铜合金为样品,得到了Cu原子辐射谱线随时间的变化情况,分析了系统中软、硬件因素对测量的谱线影响。实验证明激光器输出能量波动、每个数据点的平均次数、靶面相对于透镜焦点的位置、接受辐射的光纤束相对靶面法线的位置以及接受光纤束的有效通光口径都影响测量谱线的强度和重复精度。     

掺铒光纤自发辐射特性研究

本文对掺铒光纤的自发辐射特性进行了研究,分析了掺杂铒离子光纤的吸收截面、辐射截面、自发辐射谱、净增益系数等的特性,以及在掺铒光纤中,泵浦功率、自发辐射功率、光纤长度、自发辐射谱之间的关系,并用单色仪和波长为1.48um的InGaAsP半导体激光器测试了国产掺铒光纤的吸收谱和它的自发辐射谱。     

Comparative analysis of characteristic electron energy loss spectra and inelastic scattering cross-section spectra of Fe

The inelastic electron scattering cross section spectra of Fe have been calculated based on experimental spectra of characteristic reflection electron energy loss as dependences of the product of the inelastic mean free path by the differential inelastic electron scattering cross section on the electron energy loss. It has been shown that the inelastic electron scattering cross-section spectra have certain advantages over the electron energy loss spectra in the analysis of the interaction of electrons with substance. The peaks of energy loss in the spectra of characteristic electron energy loss and inelastic electron scattering cross sections have been determined from the integral and differential spectra. It has been shown that the energy of the bulk plasmon is practically independent of the energy of primary electrons in the characteristic electron energy loss spectra and monotonically increases with increasing energy of primary electrons in the inelastic electron scattering cross-section spectra. The variation in the maximum energy of the inelastic electron scattering cross-section spectra is caused by the redistribution of intensities over the peaks of losses due to various excitations. The inelastic electron scattering cross-section spectra have been analyzed using the decomposition of the spectra into peaks of the energy loss. This method has been used for the quantitative estimation of the contributions from different energy loss processes to the inelastic electron scattering cross-section spectra of Fe and for the determination of the nature of the energy loss peaks.     

Quantification of surface effects: Monte Carlo simulation of REELS spectra to obtain surface excitation parameter

The surface excitation effect is investigated by using the quantum mechanical frame work of complex self-energy of electrons which interact with a bounded semi-infinite medium. In the self-energy formalism, differential inverse inelastic mean free path (DIIMFP) has contributions from bulk and surface plasmons. Monte Carlo simulation of the interaction of electrons with a solid medium and surface has been performed. The surface excitation parameter (SEP) is then obtained from the simulated reflection electron energy loss spectroscopy (REELS) spectra. The calculated SEP results by Monte Carlo simulation are compared with the previous calculations of total surface excitation probability, which was estimated by a numerical integration of surface term of DIIMFP. The contribution merely due to surface excitations towards REELS spectra is extracted by subtracting the two Monte Carlo simulated REELS spectra that based on the two models of electron inelastic scattering, i.e. a full surface model (SM) and a pure bulk model (BM). The surface excitations found to be significant at low energy losses and diminish at higher energy losses whereas the bulk plasmon contributions show opposite behavior and are negligible at lower energy losses. The average number of surface excitations is then evaluated by the computation of ratio of the integrated surface contribution to the elastic peak. The calculated results for Ag are found to be reasonably in agreement with our previous results for total probability of surface excitations and other reported experimental data for SEP. Surface correction factor (SCF) is calculated using SEP for several metals and is compared with the reported ratio of SCF with Ni sample as reference.     

Raman optical activity spectra: basis set and electron correlation effects

Raman and vibrational Raman optical activity (ROA) spectra have been calculated for three molecules: H₂O₂, CHDTF and CHDTOH. The effects of electron correlation on the ROA parameters of these relatively small systems have been investigated by means of the multiconfigurational self-consistent field (SCF) approach. A range of correlation-consistent basis sets has been used in the calculations. The basis set convergence of the calculated ROA parameters is fairly well achieved when sets of at least d-aug-cc-pVTZ quality are used. On the other hand, the aug-cc-pVDZ set seems to be sufficient for a qualitative analysis. Diffuse functions, possibly a double set, are essential to ensure a good quality of the calculated ROA spectrum. In most cases the sign and approximate magnitude of the ROA are correctly predicted at the SCF level, and the corresponding ROA spectra should be considered qualitatively accurate.     

Self-consistent field theory of collisions I. Scattering channels

The conventional Hartree and Hartree-Fock approaches for treating many-electron bound systems have been extended recently to positive energy scattering problems, in which both the bound and continuum orbitals are determined by the requirement of full self-consistency. Serious consequences of such a theory are that the target orbitals become energy dependent and the asymptotic boundary conditions are satisfied only approximately, in lowest order. It is important therefore to test the theory for its convergence under configuration mixing. This self-consistent field (SCF) theory for scattering has been tested here for scattering from hydrogenic target as a model where the target function is determined dynamically. Penetration of the projectile inside the bound target orbital is manifest through the SCF for the bound state. Our results show that the theory converges to the correct amplitudes and to the exact boundary conditions as more configurations are added. The use of the amputated functions and the weak asymptotic condition (WAC) upon which the SCF theory is based, is justified as the WAC converges to the correct limit. It is then applied to the positron-helium and electron-helium scattering systems where the helium function is calculated simultaneously together with the scattering function. The resulting phase shifts and the SCF target functions are compared with those obtained with the pre-determined target functions in the conventional approaches. Received 22 September 1999     

Orthogonalized-plane-wave approximation in the calculation of photoionization cross sections of molecules

The physical bases of the OPW approximation in the calculation of molecular photoionization cross sections are considered in terms of the scattering theory, and the ways of improving the calculation within the framework of OPW approximation are discussed.Numerical calculations are done on several molecules by the ordinary OPW method and by its modifications using the bound orbitals obtained by ab initio SCFMO calculations with gaussian basis set.     

Combined Sign Coherent Factor and Delay Multiply and Sum Beamformer for Plane Wave Imaging

Plane wave imaging is a relatively new technique in ultrasound imaging. However, in traditional methods, the coherent information of different emissions and different elements are not considered. In fact, the sign coherent factor (SCF) can improve the lateral resolution of the imaging greatly. In addition, the delay multiply and sum (DMAS) beamformer is mainly based on the spatial correlation of background scattering signals, it has higher contrast and resolution, but suffers from energy loss at great depths. In this paper, combining the advantages of SCF and DMAS, the sign coherent factor delay multiply and sum (SCF-DMAS) beamformer for plane wave imaging is proposed. Unlike the traditional plane wave imaging, the proposed SCF-DMAS beamformer is based on the 2-D echo data set, which improves the imaging speed greatly. Finally, we simulated the point targets and the cyst phantom to evaluate the performance of proposed method. Compared with the traditional plane wave imaging, the lateral resolution of SCF-DMAS beamformer improves greatly for the point targets, and for the cyst phantom the contrast ratio (CR) and contrast-to-noise ratio (CNR) increased by 96.97 and by 79.98% respectively without reducing the frame rate.     

Quantum chemical calculations of vibrational spectra of <Emphasis Type="Italic">para</Emphasis>-ethylbenzenesulfonic acid

Quantum chemical calculations of vibrational spectra of para-ethylbenzenesulfonic acid have been conducted by means of a non-empirical SCF MO LCAO method with the use of the 6-31G(d) basis set. Calculated IR and Raman frequencies are assigned to vibrations of specific atomic groups. It is shown that para-ethylbenzenesulfonic acid can serve as a reasonable quantum chemical model in calculations of vibrational spectra for polystyrene sulfonic resins of various degrees of hydration.     

Optical constants of Cu measured with reflection electron energy loss spectroscopy (REELS)

Two energy loss spectra of 1000 and 3000 eV electrons reflected from a Cu surface are analysed to give the normalized distribution of energy losses in a single surface and volume inelastic scattering process. These single scattering loss distributions are subsequently fitted to theoretical expressions for the differential inverse inelastic mean free path (DIIMFP) and differential surface excitation probability (DSEP) providing the real and imaginary part of the dielectric function in terms of a set of Drude-Lorentz oscillators. The optical constants obtained in this way are subjected to several sum rule checks and compared with other experimental data and with density-functional-theory (DFT) calculations. The present optical data agree excellently with the DFT-results, while the earlier optical data deviate significantly from these two data sets for energies below 30 eV. The mean free path for inelastic electron scattering for energies below 2000 eV is derived from the dielectric data and is found to agree satisfactorily with values reported earlier.     

Application of quantum mechanical method to analysis of the intensity distribution in spectra of resonant hyper-Raman scattering of low-symmetry molecules

The quantum-mechanical method of calculating the relative intensities of lines in the spectra of resonant hyper-Raman scattering of polyatomic molecules in the Herzberg-Teller approximation is tested with respect to low-symmetry molecules. The method makes it possible to describe resonant Raman and hyper-Raman scattering spectra, as well as vibronic absorption spectra, from the same viewpoint based on a common set of parameters. The particular features of the implementation of the method are discussed based on the calculation of the spectra of resonant hyper-Raman scattering of chlorobenzene and adenine, and the expedience of the application of the method is illustrated. Satisfactory agreement is obtained between calculation results and available experimental data.