被光阑像散透镜聚焦高斯-谢尔模型光束轴上的光谱开关

从部分相干光的传输理论出发,研究了高斯-谢尔模型光束通过光阑像散透镜聚焦的光谱异变和光谱开关。研究表明,在考虑像散的情况下,聚焦场轴上也会出现光谱异变和光谱开关。光谱异变和光谱开关不仅与空间相关性、截断参量、菲涅耳数和源光谱谱宽有关,透镜像散对光谱异变和光谱开关也会产生影响。通过数值计算结果,重点对透镜像散对光谱移动和光谱开关的影响进行了分析。与无像散情况相比,像散会使出现光谱开关的临界位置发生变化,当像散较大时出现光谱开关的临界位置明显向几何焦面移动,特别是当像散增加到一定数值时,光谱开关会消失。     

Effect of astigmatism on spectral switches of partially coherent beams

A detailed study of the spectrum of partially coherent beams diffracted at an astigmatic aperture lens is performed. Considerable attention is paid to the effect of astigmatism on spectral switches of polychromatic Gaussian Schell-model beams. It is shown that the spectral switch can also take place in the vicinity of intensity minimum in a geometrical focal plane for the astigmatic case, but the astigmatism of the lens and the spatial correlation of the beam affect the critical position u_c, spectral minimum S_{min}, and transition height Δ of spectral switches.     

On-axis spectral shifts and spectral switches of Gaussian Schell-model beams focused by an astigmatic aperture lens

Starting from the propagation law of partially coherent light, the on-axis spectral shifts and spectral switches of Gaussian Schell-model (GSM) beams focused by an astigmatic aperture lens are studied. It is shown that, as compared with an aberration-free case whose spectral shifts and spectral switches are induced by spatial correlation and aperture diffraction, the spectral shifts and spectral switches of GSM beams also depend upon the astigmatism of the lens for an astigmatism case. Detailed numerical calculations are made to illustrate the behavior of spectral shifts and spectral switches of GSM beams focused by an astigmatic aperture lens.     

Propagation properties of partially polarized Gaussian Schell-model beams through an astigmatic lens

Based on the beam coherent-polarization (BCP) matrix approach and propagation law of partially coherent beams, analytical propagation equations of partially polarized Gaussian Schell-model (PGSM) beams through an astigmatic lens are derived, which enables us to study the propagation-induced polarization changes and irradiance distributions at any propagation distance of PGSM beams through an astigmatic lens within the framework of the paraxial approximation. Detailed numerical results for a PGSM beam passing through an astigmatic lens are presented. A comparison with the aberration-free case is made, and shows that the astigmatism affects the propagation properties of PGSM beams.     

Focal switching of partially coherent modified Bessel–Gaussian beams passing through an astigmatic lens with circular aperture

The axial intensity distribution of partially coherent modified Bessel–Gaussian (PCMBG) beams passing through an astigmatic lens with circular aperture is derived on the basis of Collins formula. The influences of truncation parameter δ and astigmatic coefficient α on the axial intensity distribution are presented. The research shows that the axial intensity changes with the variation of α, and twice focal switches have been found. Furthermore, the physical interpretation of the twice focal switches is given and is also illustrated by numerical calculations. It has been revealed that the existence of astigmatism and the effect of the truncation parameter are the two main reasons for the twice focal switches of PCMBG beams passing through an astigmatic lens with circular aperture.     

非均匀偏振光束通过环状光阑像散透镜的聚焦特性

借助于光束相干偏振矩阵和广义惠更斯－菲涅耳衍射积分公式,研究了非均匀偏振(NUP)光束通过环状光阑像散透镜的聚焦特性,并将圆孔光阑作为环状光阑内径为零的特例处理.数值计算结果表明,实际焦点位置、光强和偏振度分布与透镜的像散、环状光阑的菲涅耳数和遮拦比以及NUP光束参量有关.     

高斯-谢尔模型光束通过光阑像散透镜传输轴上光谱变化

从部分相干光的传输理论出发,研究了高斯-谢尔模型(GSM)光束通过光阑像散透镜传输轴上的光谱变化规律.结果表明,与光源光谱相比,高斯-谢尔模型(GSM)光束通过光阑像散透镜传输轴上光谱发生了中心频率的移动,这种现象被称为光谱位移.详细分析了透镜的像散、光束的空间相关性和光阑的截断参量对光谱变化的影响.数值计算表明,这些参量会对光谱移动产生比较大的作用.     

Modeling of astigmatic-elliptical beam shaping during fs-laser waveguide writing including beam truncation and diffraction effects

In this work, we report a model for accurately calculating the focal volumes corresponding to astigmatic elliptical beams used in fs-laser waveguide writing. The model is based on the use of the ABCD matrix formalism for the propagation of a Gaussian beam. The code includes the effects of propagation on the astigmatic elliptical beam, and the effects of beam truncation and diffraction at the entrance pupil of the focusing objective due to beam clipping when overfilling the pupil. The results predict that for a given astigmatism value and propagation distance it is possible to efficiently suppress the astigmatic focus closer to the surface. This explains previous experimental results where single structure waveguides with controllable aspect-ratio were fabricated using astigmatic-elliptical beams. Furthermore, we investigate the respective roles of astigmatism and beam propagation, as well as the strong impact of truncation and diffraction effects caused by clipping the beam at the pupil of the focusing optics. Finally, based on the results from our model, we present some practical considerations in terms of beam propagation and phase wrapping constraints.     

聚丙烯酸酯泡沫密度均匀性的射线检测技术

低密度泡沫材料大多存在一定程度的密度不均匀性，这对其后续使用性能将带来不良影响。文中简述了ICF靶用聚丙烯酸酯泡沫的制备方法，并利用β射线和X射线检测技术，对直径为mm量级的低密度聚丙烯酸酯泡沫柱进行密度分布表征。研究结果表明:泡沫柱沿轴向的密度分布比较均匀，而沿径向呈内低外高分布，形成了明显的密度梯度。实验表明:射线检测技术测量靶用低密度泡沫的方法可基本满足目前的实验要求，但密度分辨率和空间分辨率还有待进一步提高。     

像散透镜对高斯光束的变换特性

 基于广义惠更斯-菲涅尔衍射积分,并考虑了像散的影响,对高斯光束通过像散透镜后的传输特性作了解析研究,以光束传输因子和桶中功率为参数分析了像散高斯光束的光束质量,并以数值计算例加以说明。     

Spectral shifts of Gaussian Schell-model beams in passage through an astigmatic lens

Starting from the propagation law of partially coherent light, a closed-form expression for the spectrum of Gaussian Schell-model (GSM) beams propagating through an astigmatic lens is derived, which enables us to study the dependence of spectral shift of GSM beams on the astigmatism of the lens and spatial coherence of GSM beams both analytically and numerically. A comparison with the aberration-free case is made, and shows that the astigmatism affects the spectral behavior of GSM beams. Two special cases of the full coherence and incoherence are discussed and illustrated physically.     

Propagation of astigmatic stochastic electromagnetic beams in oceanic turbulence

In this paper, we investigate the characteristics of astigmatic stochastic electromagnetic beams through oceanic turbulence. Taking the electromagnetic Gaussian Schell-model (GSM) beam as an example, the analytic expressions for the spectral density and the spectral degree of polarization of the beam propagating the oceanic turbulence are derived. It is indicated that the spectral density along the z-axis of the GSM beam in the oceanic turbulence is severely influenced by the source correlation properties, as well as by the sea-related parameters. We show that the characteristics of the spectral density along the x-axis, y-axis and z-axis of astigmatic electromagnetic GSM beams passing through the oceanic turbulence are qualitatively different. Furthermore, we find that as the astigmatic coefficient becomes larger, the maximum value of the spectral density along the z-axis increases rapidly and the width of the spectral density becomes shorter rapidly. Finally, the results have shown that different strengths of astigmatism have different effects on the spectral degree of polarization.     

平顶光束通过像散透镜的传输和光束参量的变化

对平顶光束通过像散透镜的传输和光束参量(包括束宽、束腰宽度和位置、远场发散角和M2因子)的变化做了研究.结果表明,像散使平顶光束在x方向的束腰宽度增加,远场发散角减小,实际焦点的位置远离透镜,而在y方向正相反.平顶光束的M2因子与像散无关.x、y方向束宽和远场发散角的相对误差随光束阶数,瑞利长度,像散系数和透镜焦距变化.当x、y方向的光束阶数和初始束宽相等时,几何焦面上两方向束宽的相对误差相等,但在实际焦面上不同.     

Kerr非线性介质中聚焦像散高斯光束的传输特性

当高功率激光通过Kerr非线性介质传输时,Kerr效应会严重影响激光的传输特性.实际应用中常遇到像散光束.迄今为止,像散光束传输特性的研究大都局限于在线性介质中的传输,而在非线性介质中传输的研究较少,且还未涉及像散激光束通过含光学系统的Kerr非线性介质传输变换的研究.本文主要研究Kerr效应对聚焦光束像散特性和焦移特性的影响,以及聚焦像散高斯光束的自聚焦焦距和光束焦点调控.在光束扩展情况下,推导出了聚焦像散高斯光束在Kerr非线性介质中传输的束宽、束腰位置和焦移的解析公式,研究表明:在自聚焦介质中,随着自聚焦作用增强(如光束功率增强),光束像散越强,但焦移越小;在自散焦介质中,随着自散焦作用增强(如光束功率增强),光束像散越弱,但焦移越大.另一方面,在光束自聚焦情况下,推导出了自聚焦焦距的解析公式,研究表明利用光束像散可以调控光束焦点个数.     

Transformation and spatial shaping of partially coherent cosh-Gaussian beams through an astigmatic lens

Based on the propagation law of partially coherent beams, the closed-form propagation expression for partially coherent cosh-Gaussian (ChG) beams through an astigmatic lens is derived. The transformation and spatial shaping of partially coherent ChG beams through the astigmatic lens are studied and illustrated by numerical examples. It is shown that a suitable choice of the spatial coherence parameter and/or astigmatic coefficient, different beam profiles, such as Gaussian-like, flat-topped and bottle beam profiles, and beam profile with a central dip, at the geometric focal plane and at a certain plane are realizable.     

像散Bessel光束自重建特性的理论和实验研究

基于菲涅耳衍射积分理论和巴比涅原理,推导出像散Bessel光束经圆形障碍物后的光强分布一般表达式.数值模拟了像散Bessel光束经圆形障碍物遮挡后光场的自重建过程,并设计相关实验进行验证,实验结果与理论模拟基本符合.结果表明：零阶像散Bessel光束经过轴上和离轴障碍物后均会发生光束重建现象.随着传输距离的增加,像散Bessel光束的外轮廓尺寸变大、中心光点阵列数增多,逐渐重建出不同于障碍物前的完整光束.并且观察到光束在重建过程中横向和纵向的重建速度并不一致,存在一定的速度差.利用螺旋相位板产生高阶像散Bessel光束,验证了高阶像散Bessel光束经障碍物遮挡后同样具有自重建特性.研究结果对像散Bessel光束在多层面粒子操纵方面的应用具有参考价值.     

线偏振相位涡旋光束的像散特性

提出采用像散系数表征涡旋光束的像散特性。利用螺旋相位板产生了线偏振相位涡旋光束,并对其光束质量及像散特性进行了实际测量。数值模拟了不同拓扑荷数的涡旋光束的传输特性及光束质量,分析了像散系数随拓扑荷数变化的规律,结果表明:当拓扑荷数为整数时,光束无像散,像散系数为零;当拓扑荷数为半奇数时,光束的像散特性明显,像散系数达到极大值;随着拓扑荷数整数部分的增加,像散系数的极大值减小。     

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.     

Vortex-edge dislocation interaction in the presence of an astigmatic lens

The vortex-edge dislocation interaction in the presence of an astigmatic lens is studied both analytically and numerically, where the effect of astigmatism is stressed. It is shown that for the aberration-free case the edge dislocation bending and break up into a pair of oppositely charged vortices and the shift of the initial vortex appear. The astigmatism leads to some richer vortex evolution behavior. By suitably varying the astigmatic coefficient of the lens, the motion, creation, annihilation and shift to infinity of vortices take place. The off-axis distance additionally affects the vortex evolution behavior for the case of the on-axis vortex and off-axis edge dislocation interaction. In the vortex evolution process the total topological charge is not conserved in general.