Calibration of quantitative rescattering model for simulating vortex high-order harmonic generation driven by Laguerre–Gaussian beam with nonzero orbital angular momentum

We calibrate the macroscopic vortex high-order harmonic generation(HHG)obtained by the quantitative rescattering(QRS)model to compute single-atom induced dipoles against that by solving the time-dependent Schr?dinger equation(TDSE).We show that the QRS perfectly agrees with the TDSE under the favorable phase-matching condition,and the QRS can accurately predict the main features in the spatial profiles of vortex HHG if the phase-matching condition is not good.We uncover that harmonic emissions from short and long trajectories are adjusted by the phase-matching condition through the time-frequency analysis and the QRS can simulate the vortex HHG accurately only when the interference between two trajectories is absent.This work confirms that it is an efficient way to employ the QRS model in the single-atom response for precisely simulating the macroscopic vortex HHG.

Propagation of Gaussian Schell-Model Array Beams through a Jet Engine Exhaust

Here a Gaussian Shell Model Array (GSMA) beam is used to investigate the propagation characteristics in the jet engine exhaust region. It has great significance to improve various optical systems for wide application in trapping cold atoms, creating gratings, and atmospheric optical communication. We calculate analytical formulas for the spectral density (SD) and the propagation factors Mx2 and My2 of a GSMA beam. The influence of inner scale of turbulence in the jet engine exhaust region on its power spectrum has been also analyzed. According to these results, the influence of turbulence in a jet engine exhaust on a GSMA beam has been reduced by changing the parameters of light source and turbulence. For example, it is an excellent tool for mitigation of the jet engine exhaust-induced anisotropy of turbulence to increase the source coherence length, the root-mean-squared (rms) beam width, the wavelength or reduce the outer scale of turbulence.

Influence of moderate-to-strong anisotropic non-Kolmogorov turbulence on intensity fluctuations of a Gaussian–Schell model beam in marine atmosphere

The scintillation index（SI） of a Gaussian–Schell model（GSM） beam in a moderate-to-strong anisotropic nonKolmogorov turbulent atmosphere is developed based on the extended Rytov theory. The on-axis SI in a marine atmosphere is higher than that in a terrestrial atmosphere, but the off-axis SI exhibits the opposite trend. The on-axis SI first increases and then begins to decrease and saturate as the turbulence strength increases. Turbulence inner and outer scales have different effects on the on-axis SI in different turbulent fluctuation regions. The anisotropy characteristic of atmospheric turbulence leads to the decline in the on-axis SI, and the rise in the off-axis SI. The on-axis SI can be lowered by increasing the anisotropy of turbulence, wavelength, and source partial coherence before entering the saturation attenuation region. The developed model may be useful for evaluating ship-to-ship/shore free-space optical communication system performance.

Comparison between relay propagation and direct propagation of Gaussian-Schell-model beam in turbulent atmosphere along a slant path

a） The relay propagation of Gaussian-Schell-model in turbulent atmosphere along a slant path is studied in this paper. Based on the extended Huygens-Fresnel principle and a quadratic approximation, an analytical formula of average intensity for Gaussian-Schell-model beams in turbulent atmosphere along a slant path is derived, and some special cases are discussed. From the study and the comparison with the direct propagation, we can see that the relay propagation has an advantage over the direct propagation. When the altitude of the target is low, the peak intensity of relay propagation is much larger than that of direct propagation. However, because of the limitation of the relay system aperture for relay propagation and the variation of coherence length for direct propagation, the difference in peak intensity between the two propagations decreases with the increase of the target altitude.

Focusing properties of Gaussian Schell-model beams by an astigmatic aperture lens

This paper studies the focusing properties of Gaussian Schell-model （GSM） beams by an astigmatic aperture lens. It is shown that the axial irradiance distribution, the maximum axial irradiance and its position of focused GSM beams by an astigmatic aperture lens depend upon the astigmatism of the lens, the coherence of partially coherent light, the truncation parameter of the aperture and Fresnel number. The numerical calculation results are given to illustrate how these parameters affect the focusing property.

Effect of the Relative Position with Gaussian Beam Center and Droplet Center on Optical Caustics

In this paper, a vector ray-tracing model (VRT) is used to simulate the optical caustic structures associated with the secondary rainbow for an ellipsoidal droplet illuminated by a Gaussian beam. The optical caustics of drops with an equatorial radius a = 50 μm, 100 μm, 200 μm, and 500 μm are studied at the same drop/beam ratios (i.e. γ the ratio between the droplet equatorial radius and the Gaussian beam waist) using concentric illumination with a Gaussian beam, and the effect of droplet size on the optical caustics is analyzed. The curvature of the rainbow fringe and the evolution of the cusp caustics position, in this case, are obtained;the diameter range of droplet shape (ellipsoid) measured by Gaussian beam illumination is broadened. Based on this model, the effects of the relative positions d = 0, 0.5yR, and yR on the optical caustics of the droplet when the center of the Gaussian beam deviates from the droplet center (the center of the Gaussian beam waist is on the same y-axis as the droplet center) are discussed. The optical caustics of the droplet when the center of the Gaussian beam is off the droplet center (the center of the Gaussian beam waist is on the z-axis with the droplet center) are also discussed. The effects of the relative positions of the center of the beam waist and the droplet center d = 0, 0.5yR, and yR on the optical caustics are also discussed. A method of measuring droplet shape with Gaussian beam illumination is proposed when the beam waist center is coaxial with the droplet center.

面向复杂地质目标的地震采集观测系统优化方法及应用

采集观测系统优化设计是提高地震资料质量和降低采集成本的一个重要手段。提高复杂地质目标陡坡带阴影区的反射能量是目前观测系统优化设计的一个难点。为此,提出了一种面向复杂地质目标的地震采集观测系统优化方法。首先,在三维模型上利用菲涅耳带半径,对高斯束照明能量重新优化,提高正演模拟的精度,提取各目的层面元接收能量和逆向照明能量。其次,根据不同地质目标和地表障碍物情况采用三种方法对观测系统进行优化:(1)基于目的层面元接收能量均匀性的炮点自动加密;(2)基于目的层逆向照明能量的炮点加密范围优化;(3)基于地表障碍物范围和目的层能量均匀性双重约束的炮点优化。将该方法用于胜利探区BS和G94北两个区块,有效提升了地震资料成像精度。

水声射线传播的黎曼几何建模·基础理论

水声建模一般采用外嵌描述,即以欧氏空间固定坐标系等要素刻画水声信道.黎曼几何是弯曲空间上的内蕴几何学,更能反映流形的本质性质.水声学高斯波束模型借鉴自地震学,可有效避免传统射线追踪的弊端,在以Bellhop为代表的水声模型中得到广泛应用,是水声射线建模与应用的主流方法之一.传统水声射线建模的欧氏空间底流形假设,难以有效刻画高斯波束的弯曲特性.本文通过建立水声射线传播的黎曼几何基本理论,得到程函方程、动态射线方程及高斯波束模型的黎曼几何内蕴形式,分析了水声射线几何拓扑性质,指出水声射线模型中的焦散点等价于黎曼几何中的共轭点,高斯波束几何扩展是测地线沿雅可比场的偏离,波束声线会聚体现为声场正截面曲率作用下偏离的测地线在共轭点的交汇.为验证理论正确性与适用性,本文以水平分层距离相关环境为例,给出特定环境和坐标系下应用前序理论建模的具体方法.3个典型水声传播算例的仿真对比分析,表明水声传播黎曼几何理论模型是准确有效的,相比Bellhop模型所采用的计算方法,具有更为清晰的数学物理含义.本文基础理论可方便推广至曲面、三维各向异性等情形,为后续在三维弯曲球体流形、四维时变伪黎曼流形等声传播环境下的黎曼几何射线建模研究奠定了理论基础.

The simulation of ultrasonic beams with a Gaussian beam equivalent point source model

Point Sources and Gaussian beams are used frequently as fundamental building blocks for developing ultrasonic beam models. Both these models have different weaknesses that limit their effectiveness. Here, we will show that one can develop a Gaussian Beam Equivalent Point Source （GBEPS） model that removes those weaknesses and combines the accuracy and versatility of the point source models with much of the speed and well-behaved nature of Gaussian beam models. We will demonstrate the efficiency and versatility of this new GBEPS model in simulating the beams generated from ultrasonic phased arrays, using as few as one Gaussian beam per element of the array. A single element GBEPS model will be shown to be as accurate as a point source model even when substantial beam focusing or steering is present in the array or where the array beam is transmitted through an interface. At the same time the GBEPS model will be shown to be several orders of magnitude faster than the point source model.

基于高斯混合模型的汽车车架纵梁故障监测方法研究

针对现有汽车车架纵梁故障监测方法效果不佳的问题,提出基于高斯混合模型的汽车车架纵梁故障监测方法。首先利用传感器采集汽车车架纵梁数据,并对其进行预处理。然后基于主成分分析法完成数据降维,在T统计故障监测的基础上引入高斯混合模型设计了一种汽车车架纵梁故障监测方法,通过将T统计控制限、SPE统计量控制限与设置阈值比较,实现故障监测与识别。实验结果表明,该方法对汽车车架纵梁故障监测的准确率达到94%以上,并且不受月份条件的影响,优于对比方法,证明该方法实用性强、故障监测准确率高。

井间地震高斯射线束正演方法

本文根据高斯射线束方法的基本原理和数学表达式，结合井间地震方法的特殊观测方式，开发了井间地震方法的正演模块，给出了不同观测条件下各种模型的试验结果。该模块在二维非均匀各向同性介质中，可以同时或单独计算直达Ｐ波、Ｓ波，上行反射Ｐ波、Ｓ波和转换波，下行反射Ｐ波、Ｓ波及转换波。计算出的地震波场不仅能反映波的运动学特性，还能反映波的高频动力学特征。

部分相干高斯-谢尔光束在大气湍流中的展宽与漂移

基于广义惠更斯-菲涅耳原理,交叉密度函数以及Rytov's相位结构函数二次近似,利用傅里叶高斯变换推导出部分相干高斯-谢尔(GSM)光束在大气湍流中的强度分布表达式,并在此基础上分析了大气湍流对光束展宽、以及光束漂移的影响。数值模拟表明:光束展宽和光束漂移与光束的初始半径、波长、光源的相干宽度以及发射机的位置高度有关,并提出了减小湍流影响的措施。

各向异性堆焊结构中超声传播模拟与缺陷回波预测

奥氏体不锈钢呈现出明显声学各向异性,如何检测与评价这类材料成为声学检测领域的研究难点和热点问题。应用多高斯声束模型来研究超声换能器向各向异性圆管堆焊结构中辐射声场的特征。给出声场模型中材料各向异性系数的具体求解方法;并应用该声场模型计算超声束在有机玻璃楔块、各向异性堆焊层和低合金钢基体三层介质中的传播特征,重点分析堆焊层各向异性和圆管曲率变化两种因素对纵波声束偏转和聚焦形态的影响。进一步,将多高斯声束模型与分离变量法缺陷散射模型相结合,建立适用于各向异性圆管堆焊结构的超声测量模型,用于预测各向异性堆焊层下的横通孔缺陷回波信号。试验测量结果与模型预测结果的比较表明,两者的信号幅度和相位都符合较好。

能量约束下的高斯射线束法地震波场正演

高斯射线束法同时考虑波的运动学和动力学特征,并且无需两点试射追踪,因此运算速度快、精度较高。Zoeppritz方程反映了地层界面上反射波和透射波的能量。本文将高斯射线束正演与Zoeppritz方程联系起来,将高斯射线束正演得到的波场记录赋予能量信息,并利用模型对波动方程、常规射线法和本文方法的计算精度和效率进行了对比,验证了本文方法的可行性和有效性。

光成形的光固化理论分析与实验研究

通过对高斯光斑的曝光固化理论分析 ,得到了固化物形状、大小与光强分布和曝光量的关系 ;利用光纤直接曝光固化实验 ,得到了紫外光固化树脂的临界固化能量和吸收系数两个特征值 ;通过Matlab的计算建模和固化实验分析 ,验证了理论分析的正确性 。

拉盖尔-高斯光束与高斯光束捕获力比较

根据高斯光束和拉盖尔-高斯光束两种光源的截面光强表达式,模拟出各自的光强分布.利用几何光学模型分别计算了高斯光束和拉盖尔-高斯光束在不同捕获目标尺寸和折射率、显微镜物镜的数值孔径以及样品池界面处到捕获目标的距离时的捕获效率,对高斯光束和以拉盖尔-高斯光束为代表的空心光束的捕获能力进行了比较.结果表明,拉盖尔-高斯光束相对于高斯光束其捕获能力具有很大的优势,拉盖尔-高斯光束的最大反向捕获效率高于高斯光束的最大反向捕获效率,在光镊稳定平衡点附近的刚度大于高斯光束的刚度.拉盖尔-高斯光束由于其特殊的光强分布,当物镜的数值孔径足够大时球差对其影响较大.

钢轨轨头内多元高斯声场模拟及其缺陷响应

钢轨不规则的几何外形造成超声检测时缺陷信号难以准确提取。根据多元高斯声束理论,结合轨头的几何参数及声学性能、探头及耦合剂的特性参数,建立了超声波在轨头内传播的多元高斯声束模型,以此研究不同探头频率、晶片直径下轨头区的声场分布规律,探求入射角、踏面曲率对声场的影响,并分析各情况下探头的有效检测区域;基于建立的轨头内多元高斯声束模型,结合基尔霍夫近似获得的散射模型,建立超声测量模型,实现轨头内缺陷响应的回波预测。通过对轨头内的横通孔进行模型预测与实验检测,两信号主体部位的峰值峰位均良好吻合,验证了该方法的有效性,研究成果对钢轨超声检测工艺有积极的理论指导意义。

高斯波束在双负媒质中的传播特性分析

提出了一种基于Drude色散媒质模型的2维TM模时域有限差分法,数值模拟了高斯波束从自由空间垂直入射和斜入射到双负媒质(介电常数和磁导率同时为负)平板后的折射现象,并给出了平板内外的电场强度分布。模拟结果显示:垂直入射时,双负媒质平板对高斯波束具有汇聚作用,通过改变媒质的折射率,可以控制高斯波束通过组合平板的传播时间而不发生衰减;斜入射时,折射波束与入射波束均位于法线的同一侧,高斯波束在双负媒质与空气交界面处发生了负折射。

高斯束层析与全波形反演联合速度建模

基于叠前地震波场模拟的全波形反演(FWI)技术走向实用化充满挑战性。陆上地震资料的低信噪比、缺失低频、复杂近地表及三维数据的巨大内存需求和海量计算等因素都制约了FWI技术的应用推广。为此,研究并开发了高斯束层析速度建模技术,弥补了传统射线层析无法反演得到的中波数速度成分,为FWI提供了高精度宏观速度模型,有效避免了周波跳跃现象;利用基于相位匹配的互相关目标泛函取代L2范数求解梯度,降低了反演对低频数据的依赖,有效解决了FWI海量计算难题;利用伪保守波动方程形成自伴随的正演算子,大幅度提升了基于伴随状态法的梯度计算能力,增强了反演对陆地数据的适应性,实现了陆地资料的FWI高分辨率速度建模能力。