面光源对人肺组织中光能分布的影响

用Monte Carlo方法仿真了两种面光源(高斯光束和圆平面光束)在人肺组织中的传播,讨论了不同面光源以及不同大小的光束入射到该组织时,其光能流率和漫反射强度的分布情况.结果表明激光光斑形状和大小的选择对激光的临床应用将有很大影响.     

光纤耦合LD输出光场特性研究

根据光纤传输的模式理论,分析了单芯光纤输出端面的光场分布.利用单模光纤测量了纤端光场的强度分布,拟合了光纤输出端面光强分布的近似表达式.根据此数值计算和实验测量了多芯光纤输出端面的强度分布,结果基本吻合.表明光纤出射端面的光强分布应是介于高斯分布和几何分布之间的一种准高斯分布.     

光纤耦合激光束输出光空间分布及其影响因素分析

通过分析光纤出射端面的光强分布,研究了光纤传输过程中激光二极管出射光束进入光纤时的指向角对出射端面光场分布的影响.提出一种影响光纤输出端光场的新因素,对数值孔径和光纤芯径两个影响因素进行了补充.在光纤传输过程中,将激光二极管出射的光束等效为大量光线,在二极管输出光的位置以及空间分布确定的情况下,使用光线追迹方法依次分析了单束和多束光的指向角以及光纤长度对出射面光强分布的影响.结果显示:单束入射光指向角的偏差会引起光纤输出端面光强极值位置的偏移,多束的情况可以导致光纤输出端光强呈现明显的环状分布,得出了入射光束指向角的偏差是影响光纤出射面光强分布和峰值位置的重要因素的结论,而光纤长度的变化对上述分布状况同样存在影响.     

倒锥透镜型塑料光纤连接器光学特性研究

提出一种基于倒锥透镜光纤端的新型塑料光纤连接器.为了增大光纤的数值孔径,降低光纤端面对于对准准确度的要求,连接器的光纤连接端面制成倒锥透镜形状.利用截断法对该类型连接器的光学特性进行了测试.1 m长光纤跳线总损耗有75.7％集中在5.4 dB～6.0 dB之间,连接损耗70.7%集中在2.1 dB~2.7 dB之间,同一组跳线插拔200次连接损耗有95％集中分布在2.2 dB～2.58 dB.实验结果表明：倒锥透镜型塑料光纤连接器可以满足“光纤入户”对连接器性能的要求.     

多极矩分析的教与学探讨

多极矩展开是一种重要的分析方法，由静态电磁场多极矩展开得到的电多极子和磁多极子是基础而重要的物理模型.多极矩展开表示方法、多极子模型与多极子以及电磁场相互作用是多极矩分析教学的核心内容.本文从上述三个方面展开探讨：给出静态电场和静态磁场的内部和外部多极展开；讨论多极矩展开的不同表示的关系；强调多极子是基于远源处电磁势对源进行的等效点源替代；最后，从受力与力矩方面考察电多极子和磁多极子与外电磁场的相互作用.     

光纤端面Nd:YAG激光诱导损伤分析

采用Nd:YAG激光对全石英多模光纤进行激光诱导损伤实验.结果全部为光纤端面损伤,主要是由光纤端面的杂质缺陷引起的.通过对激光损伤形貌的分析,明确光纤端面损伤机理.采用Matlab对光纤损伤端面进行图像处理,获得光纤端面损伤点的大小、出现频率和位置分布的统计特性.通过分析发现,光纤端面损伤点位置分布服从一定的规律,光纤前端面和后端面不同;光纤端面不同大小损伤点出现频率服从高斯分布;注入激光特性参数决定光纤前端面损伤特性,光纤传能特性以及光纤端面质量决定其后端面损伤特性.     

脉冲激光诱导光纤损伤的测试方法

 针对传能光纤的高峰值功率激光损伤过程,研究了光纤损伤测试方法。实验装置搭建中增加了定位孔,有利于激光注入光纤对准;分别采用刀口法和CCD法对入射光束不同截面处光斑大小进行了测量,两种方法的测量结果基本一致。参考GJB1487-92激光光学元件测试方法和ISO11245光学表面的激光诱导损伤阈值测试方法,采用N-ON-1损伤测试和有效光斑面积计算方法对芯径为400 μm的石英包层阶跃折射率石英光纤进行了损伤阈值测试。实验发现：光纤损伤部位全部为入射端面,利用200倍显微镜观察光纤端面,出现明显永久性损伤点。最后采用统计学原理和线性拟合等方法得出测试光纤的端面零概率损伤阈值为3.85 GW/cm²。     

双端抽运热容激光器温度特性分析

通过对激光二级管阵列双端抽运热容激光器晶体的分析,建立了热传导模型及边界条件.利用有限元方法模拟了晶体的温度场分布,并分别对抽运光斑直径、抽运持续时间、抽运光强和晶体端面尺寸等因素对温度场分布的影响进行了分析,得到了热容工作模式下的激光器温度特性.结果表明,晶体端面温差随抽运光斑直径的增大先增后减,存在一个极大值,并且在不同抽运光强下,出现端面温差极大点时的抽运光斑直径不变.     

空气孔正方形排列的低损耗高双折射光子晶体光纤的数值模拟

提出了一种正方形排列渐增空气孔高双折射光子晶体光纤，并利用多极方法对光纤基模的模场分布、色散、双折射以及损耗特性进行了数值模拟.模拟结果表明利用这种结构可以在包层空气孔层数较少的情况下实现极低的限制损耗，通过调节内层空气孔的分布可以有效地控制光纤的双折射和色散特性.本结果对高双折射光子晶体光纤的制备具有一定的指导意义. 关键词： 光子晶体光纤 双折射 限制损耗 多极方法     

光纤耦合激光束输出光空间分布及其影响因素分析

通过分析光纤出射端面的光强分布,研究了光纤传输过程中激光二极管出射光束进入光纤时的指向角对出射端面光场分布的影响.提出一种影响光纤输出端光场的新因素,对数值孔径和光纤芯径两个影响因素进行了补充.在光纤传输过程中,将激光二极管出射的光束等效为大量光线,在二极管输出光的位置以及空间分布确定的情况下,使用光线追迹方法依次分析...     

Evolution of modes in double-clad Raman fiber amplifier

Stimulated Raman scattering in a double cladding optical fiber is studied with a continuous wave laser used as a pump source. Under various launch conditions, pump modes are differently excited. Considering the mode coupling effect among the pump modes, the evolution of the power in the Stokes modes is studied. The results show that the scattered waves （the Stokes waves） in the fiber core with 9%tm diameter and 0.14 NA could propagate predominantly in the fundamental mode of the fiber by carefully adjusting the pump light launching conditions.     

Wide-aperture cathodoluminescent light source based on an open discharge

The feasibility of an effective high-luminance light source based on an open discharge is considered. Experimental data for the light characteristics of different cathodoluminescent screens are presented. Phosphor coatings are excited by an electron beam initiated by a planar cathode-grid injector in an inert gas atmosphere. The feasibility of maintaining an open discharge using continuous or pulsed-periodic excitation of the gas medium in the light emitter is discussed. The use of the specular method to excite the phosphor coating of the screen makes it possible to achieve a higher luminance and a higher luminous efficacy in comparison with these characteristics for cathodophosphors. The design of the cathode-grid unit allows for a large surface area of the electron injector, making it promising for wide-aperture light sources.     

掺钕保偏光纤放大器的研究

对掺钕双包层光纤放大器中抽运光和信号光沿光纤传播的功率分布进行了数值模拟,以808nm半导体激光器为抽运源,掺钕双包层保偏光纤为增益介质,对种子注入主振荡光纤放大器进行了理论分析和实验研究.利用实验室自制的皮秒锁模激光器为种子源,注入1064nm皮秒锁模脉冲,获得了稳定的放大脉冲.小信号时的放大倍数为300（增益为25dB）,获得了平均功率5W的皮秒脉冲.同时利用TDS5104型示波器探测信号光放大前后的波形,并用光谱分析仪得到输出脉冲激光的光谱图. 关键词： 光纤放大器 掺钕保偏光纤 种子注入 反向抽运     

Different supercontinuum generation processes in photonic crystal fibers pumped with a 1064-nm picosecond pulse

Picosecond pulse pumped supercontinuum generation in photonic crystal fiber is investigated by performing a series of comparative experiments. The main purpose is to investigate the supercontinuum generation processes excited by a given pump source through the experimental study of some specific fibers. A 20-W all-fiber picosecond master oscillator-power amplifier （MOPA） laser is used to pump three different kinds of photonic crystal fibers for supercontinuum generation. Three diverse supercontinuum formation processes are observed to correspond to photonie crystal fibers with distinct dis- persion properties. The experimental results are consistent with the relevant theoretical results. Based on the above analyses, a watt-level broadband white light supercontinuum source spanning from 500 nm to beyond 1700 nm is demonstrated by using a picosecond fiber laser in combination with the matched photonic crystal fiber. The limitation of the group velocity matching curve of the photonic crystal fiber is also discussed in the paper.     

Influence of Er-doped superfluorescent fiber source's spectrum-stability on the SNR of fiber optic gyroscopes

The output spectrum-stability of Er-doped superfluorescent fiber source (SFS) was measured by changing the temperature around the excited Er-doped fiber (EDF). With the experiment results, the influences of the SFS's spectrum-stability on the signal-to-noise ratio (SNR) of fiber optic gyroscope (FOG) were simulated. The simulated results demonstrate that the SNR of FOG will change no matter the power, mean wavelength or the spectral bandwidth of the light output from the Er-doped SFS is changing. The results show that the changing of SNR caused by the output power's variation is three orders of magnitude larger than that caused by the variation of mean wavelength or bandwidth. And the main factor influencing the stability of FOG's SNR is the temperature-stability of the output power of Er-doped SFS.     

熔石英亚表面缺陷附近光强分布的数值模拟

 熔石英亚表面缺陷对光场的调制是导致激光辐照场破坏的主要因素。采用有限元方法对熔石英亚表面缺陷（平面和锥形划痕）周围的光强分布进行了数值模拟。结果表明：划痕形状、几何尺寸、方位角、光的入射角等是影响划痕周围光强分布的主要因素;前表面划痕对光强的增强效果比后表面弱;在理想形状的划痕截面和表面同时发生内全反射时,平面划痕周围的光强增强效果明显。锥形划痕周围的光强分布为正确解释交叉划痕的夹角平分线附近的损伤提供了理论依据。     

In situ diagnostics in plasmas of electronic-ground-state hydrogen molecules in high vibrational and rotational states by laser-induced fluorescence with vacuum-ultraviolet radiation

Detection of excited electronic-ground-state hydrogen molecules with v(") up to 13 in a magnetic multipole plasma source was performed for the first time by laser-induced fluorescence with vacuum-ultraviolet radiation. The measurements are taken after fast shutoff of the discharge current. The rovibrationally excited molecules live longer than the plasma background light so that the fluorescence light can be detected with good signal-to-noise ratio. Absolute level populations are measured as well as decay times. The theoretically predicted suprathermal population of the vibrational distribution is clearly identified. The H- density is calculated on the basis of the measured populations and the measured electron energy distribution function. It is in excellent agreement with the H- density measured by photodetachment.     

Plasmons at a hole in a screen

The field distribution and the spectrum of plasma eigenmodes are determined for a circular hole in a screen having the form of a hyperboloid of revolution. The spectrum of plasmons is obtained for a planar screen with a circular hole. The symmetric mode with m=1 can be excited in the field of a dipole oriented along the screen plane, whereas the antisymmetric mode with m=0 can be excited by a dipole perpendicular to the screen plane.     

Experimental study of coherent transition radiation from relativistic electrons in a dihedral angle

Angular intensity distributions for transition radiation excited by a beam of relativistic electrons in the emitter in the form of a dihedral angle are measured in the millimeter range. The angle is formed by the intersection of two conducting planes. The source of radiation is a microtron with an electron energy of 7.4 MeV. We analyze the effect of the magnitude of the dihedral angle of the emitter, the position of the electron transition point on the surface of the angle, and the direction of motion of electrons on the angular distribution of radiation intensity. It is shown that the spectral and angular distributions of radiation intensity in the dihedral angle substantially differ from analogous distributions for a particle intersecting a planar conducting surface. The possibility of using radiation to measure the energy, spatial position, and direction of motion of charges is considered.