高斯射线束方法在深海匹配场定位中的应用

匹配场定位作为一种水声被动定位方法,其拷贝场计算方法的精度和速度对定位效果和定位效率有着直接的影响。尤其在深海,目前浅海中常用的拷贝场计算方法如简正波法、抛物方程近似等在深海中往往存在计算效率不够、内存需求大、难以满足实际应用的需求。高斯射线束方法具有计算速度快,物理意义清晰,易于并行化处理等优点,非常适合于深海近程声场计算。通过数值仿真算例和海上实验数据的处理验证了高斯射线束方法用于拷贝场计算的有效性。仿真和实验数据处理结果表明,采用高斯射线束方法计算拷贝场在深海匹配场定位中有很好的定位效果.      

束旋转90°对束变换环孔腔输出性能的影响

 使用积分方法和差分方法结合的快速计算方法，在实际燃烧驱动氟化氢化学激光器增益介质沿径向分布不均匀的情况下，考虑在光束变换环形孔径激光谐振腔的紧束段引入光束旋转90°对其输出性能的影响。计算结果显示：在无腔失调的情况下，在紧束段引入光束旋转对束变换环孔激光谐振腔输出功率及光束质量的改善并不显著；在存在腔失调的情况下，紧束段光束旋转对于输出功率和光束质量的改善有显著效果。     

高能中性束注入加热

本文仔细地研究了高能中性束注入加热的有关问题,利用多束模型计算了中性束注入加热。本文的主要特点是在捕获快离子与本底离子和电子能量交换表示式中,直接用误差函数积分进行计算,而不像以前的计算中作大参量和小参量展开近似。当快离子能量比较低时,大参量展开不再适用,因此本文的计算更为精确,更为有用。给出了多束注入加热的计算结果及其结果的讨论。本计算方法可与输运方程联立求解,数值模拟等离子体行为。     

非近轴近似多高斯声束模型的相控阵换能器声场计算

针对近轴近似的多高斯声束模犁无法准确计算离轴区域声场的问题,我们提出了一个矩形源的非近轴近似多高斯声束模型,用于计算偏转聚焦时线性相控阵换能器辐射的声场.利用该方法计算了由矩形阵元组成的相控线阵的辐射声场,并与瑞利积分、近轴近似方法及夫琅和费近似方法进行了分析和对比,计算结果表明该方法克服了常规近轴近似条件的限制,可以准确、快速地计算较大偏转范围内的换能器辐射声场,在计算相控阵换能器偏转聚焦声场中具有独特的优势.     

周期场中强束流的特性研究

用薄透镜近似空间电荷相互作用的方法研究了强束流在周期场中的传输特性.通过计算可以说明束晕的形成.同时,也为研究比K–V分布更为复杂、真实的束流分布的传输特性提供了一种新的计算方法.     

随机表面散射光场的格林函数法与基尔霍夫近似的比较

从简谐光波满足的亥姆霍兹方程出发，将由格林定理得到的介质分界面上的积分方程转化为以表面上的光波及其导数为未知量的线性方程组，并对其进行数值求解，实现了光场的数值计算. 同时，由透射光场的格林函数积分得出了基尔霍夫近似下光场的表达式. 通过类比推导夫琅和费面上散斑场自相关函数的方法，提出了产生随机表面及其导数的傅里叶变换方法. 在此基础上，对采用基尔霍夫近似进行自仿射分形随机表面的散射光场数值计算的精确程度进行了研究. 发现在随机表面粗糙度比较小时，基尔霍夫近似的精度比较高；在粗糙度相同的情况下，表面的分形 关键词： 格林函数积分 基尔霍夫近似 自仿射分形随机表面     

计算水下凹面目标散射声场的声束弹跳法

为了解决含有多次散射时水下目标声散射场的计算问题,提出了一种声束弹跳方法。把入射声波划分为若干声束,根据几何声学方法计算每条声束在目标表面的反射方向和能量损失,利用物理声学方法计算最后一次反射的声束所对应的面元的散射场,通过计算所有声束产生的散射场的叠加得到整个目标的散射场。计算了直角凹面圆锥体的散射声场,并对具体模型进行了水池测量实验,理论计算和实验测量结果一致。表明该方法作为一种高频近似的数值计算方法,可以计算存在多次散射时水下目标的散射声场。      

平面光波导光场分布的有限时域差分法计算

用有限时域差分法计算了简单三层对称平面光波导中的光场,得到了任意截面上光场的分布.这一方法的优点在于它能完全模拟波导中光场的时域特性,使波导中的光传播完全可视化,模拟横向传播,提取光在波导中的传输模式,也可用于有源波导的计算如光波导放大器.有限时域差分法直接求解依赖时间的麦克斯韦旋度方程,利用二阶精度的中心差分近似,把旋度方程中的微分符直接转换为差分形式.每一步计算都无须作矩阵求逆运算,因此,比其他数值计算方法更有效、精度更高.     

混合笔束模型在电子剂量算法中的应用

将双群模型计算的宽束电子的能量沉积与FermiEyges理论的侧向解相结合来构造电子笔束模型,即混合笔束模型.由于混合笔束模型的计算精度和效率较好,并且适用范围较大,因此,混合笔束模型展示了在放射治疗临床应用上的可能性.在混合笔束模型的基础上,改进了混合笔束模型对电子侧向分布的参数计算.计算结果表明,改进的混合笔束模型的精度符合临床应用的要求,同时,其计算速度非常快.因而显示出较好的临床应用价值 关键词： 笔束模型 双群模型 混合笔束模型     

光脉冲传输模拟的快速数值差分递推算法及其应用研究

利用零邻域的马克劳林展开对归一化非线性薛定谔方程的频域差分形式进行分析，得出一个能够同时考虑光学媒质的色散作用以及非线性克尔作用的时域快速数值差分递推公式.选取若干算例，将运用该公式的数值计算结果与已知的解析结果和传统分步傅里叶方法所得的计算结果做了相应的比较，结果表明这种快速数值差分递推公式不但拥有相当快的计算速度，也有很高的计算精度，而且在物理上符合光脉冲在光学媒质中传输时色散和非线性作用同时施加影响的客观实际，这说明它是研究非线性光学媒质中光脉冲传输的一种科学、合理而快速有效的数值计算方法. 关键词： 快速数值差分递推公式 零邻域马克劳林展开 非线性薛定谔方程 光脉冲传输     

光束变换环形孔径有源激光谐振腔模式的数值模拟

建立了燃烧驱动环柱型高能化学激光器环形增益介质的五种分布模型,使用差分和积分相结合的方法计算了束变换环孔腔在不同增益分布和折射率分布时的模式特征,研究了增益分布和折射率分布对束变换环孔腔输出性能的影响,结果表明束变换环孔腔在不同的增益介质及折射率分布情况下,仍然可以保持良好的输出光束质量,很高的提取效率,在化学激光器增益流存在激波扰动的情况下,输出光场的施特雷尔比仍达到0．8991,同时腔镜上光强分布较为均匀,可以避免镜面因热应力分布不均匀而造成镜面变形和破坏。该腔不但适用于高能化学激光器,也可以用于高能固体激光器,起到克服固体增益介质热畸变与热应力的作用,可获得优良的输出光束质量。     

具有高空间分辨力的整形环形光式差动共焦测量法

提出一种新的具有高空间分辨力的整形环形光式差动共焦测量方法。该方法通过整形环形光式共焦测量法和锐化爱里斑主瓣，改善系统横向分辨力；通过差动共焦测量法改善系统的轴向分辨力，最终达到提高系统空间分辨能力的目的。理论分析和实验表明：整形环形光内孔归一化半径ε越大，横向分辨力改善越明显，量程扩展范围越宽；当入射光波长λ=632.8nm，物镜数值孔径取NA=0.85，ε=0.5时，该系统的横向分辨力优于0.2μm，轴向分辨力优于2nm。该方法为光触针测量系统空间分辨力的提高提供了1种新的方法，可广泛应用于超精密三维微细结构工件的超精密测量。     

Scintillation index of astigmatic annular beams in a turbulent atmosphere

The scintillation properties of astigmatic annular beams in a weak turbulent atmosphere are investigated. Expression for the on-axis scintillation index of an astigmatic annular beam is derived. It is found that the scintillation index of an astigmatic annular beam can be smaller than that of a Gaussian beam, an elliptical Gaussian beam and a stigmatic annular beam in a weak turbulent atmosphere under certain conditions. The scintillation properties of astigmatic annular beams are closely controlled by its beam parameters.     

Improvement of confocal microscope performance by shaped annular beam and heterodyne confocal techniques

In order to further improve the performance of a confocal microscope (CM) used for measurement of surface profiles and 3D microstructures, a shaped annular beam heterodyne confocal measurement method based on annular pupil filter technique and reflection confocal microscopy, is proposed to expand the measurement range and to improve the defocused property of CM. The approach proposed uses a confocal dual-receiving light path arrangement and a heterodyne subtraction of two signals received from detectors with axial offset to enable CM to be used for bipolar absolute measurement and to improve the defocused property of CM, and it uses the annular pupil filter technique to produce a binary optical shaped annular beam, which expands the measurement range by expanding the full-width at half-maximum of intensity curve received from two detectors in a heterodyne confocal microscopy system. Theoretical analyses and experimental results indicate that a shaped annular beam heterodyne microscope has a measurement range expanded from 4 to 14 μm, achieved an axial resolution of 2 nm and improved the defocused property, when ε=0.5 and NA=0.65. It can be therefore concluded that the shaped annular beam heterodyne confocal measuring method proposed is a new approach to ultraprecision measurement of surface profiles and 3D microstructures.     

Long-range propagation of annular beam for lidar application

Long-range propagation characteristics of an annular beam were examined from the viewpoint of lidar application. The annular beam permits to use a reflecting telescope for transmission and improves the transmission efficiency because it can pass through the telescope without the obstruction of the telescope’s secondary mirror. As the annular beam can enlarge up to the telescope diameter, it can be eye-safe and its divergence is also reduced.The annular beam generated by a couple of Axicon prisms; conical prisms, transforms its beam shape into the central peak narrow beam; nearly non-diffractive beam, through the far-field propagation. We evaluated how the central peak intensity and its width of the transformed beam change in long-range of 3-100 km. The difficulty of the optical arraignment and the requirement of the beam quality to obtain the enough performance of the beam shape transformation were also examined theoretically and experimentally for the lidar application. The stability of the transformed beam was also confirmed in the atmospheric fluctuation.     

Bessel光束经椭圆环形孔径后的衍射光场

基于菲涅耳衍射积分理论及硬边孔径的复高斯函数展开法导出了Bessel光束经椭圆环形孔径后的光场表达式, 数值模拟了其光场的强度分布. 研究了Bessel光束经椭圆环形孔径后的光场变化及其传播过程; 在实验上利用轴棱锥输出的近似无衍射Bessel光, 通过椭圆环形孔径, 使用电荷耦合器件拍摄得到不同传播距离处的光强分布. 理论结果和实验结果均表明无衍射光束经椭圆环形孔径后会产生空心光束.     

Property study of coherent annular beam generated by the annular phase-locking laser

An annular phase-locking laser with annular gain media is presented. In this paper, the light field distribution of coherent annular beam (CAB) can be given by an analytical expression based on the Collins formula. Typical numerical examples are given to illustrate the application of our analytical result and the propagation property of a CAB through a paraxial ABCD optical system.     

Analysis on thermal characteristics of annular beam pumped vertical-external-cavity surface-emitting lasers by finite element method

The annular beam as a pump light of VECSELs is presented for the first time in this study. The thermal characteristics of VECSELs were calculated and simulated by finite element method, and the influence of the annular beam's annulus radius, the annulus width, and the pumping power to the VECSELs’ thermal characteristics was analyzed in detail. The results indicated that the annular beam can improve the VECSELs’ thermal characteristics efficiently, and provide a favorable term to generate laser in the central part of the annular. The theoretical results provided theoretical reference and experimental study for the design of high-power optically pumped VECSELs.     

Excitation of microwave by an annular electron beam in a plasma-filled dielectric lined waveguide

An axial relativistic electron beam passing through a slow wave structure is unstable to an electromagnetic perturbation whose phase velocity equals the velocity of the beam. This phenomenon of Cherenkov emission is the basis of all traveling wave tubes. In this paper an excitation of Cherenkov radiation by a thin annular relativistic electron beam in a plasma-filled dielectric-lined waveguide is analysed by use of the self-consistent linear theory. The effect of the thin annular electron beam on the beam-wave interaction is completely described by a jump condition. The dispersion equation and the simultaneous condition of the beam-wave interaction are derived. Finally, the growth rate of the wave is obtained, and the effect of the background plasma density and the electron beam radius on the growth rate of the wave are presented.This work is supported by National Natural Science Foundation of China.     

非均匀偏振光束通过环状光阑的传输

 使用光束相干偏振矩阵方法,推导出非均匀偏振光束通过环状光阑后偏振度和光强分布的表达式,研究了非均匀偏振光束通过环状光阑后偏振度和光强的变化。结果表明,在横平面上通常偏振度为非均匀分布,但在中心区域近似为均匀分布,均匀分布范围与非均匀偏振光束参数、光阑遮拦比和传输距离有关。初始为均匀分布的光强通过光阑后变为具有中心主极大和小衍射旁瓣的非均匀分布。