衍射光学器件光线追迹公式的实验验证

本文介绍了一种衍射光学器件光线追迹的方法，并给出了计算公式。作为验证，在实验室里制作了具有连续相位的体全息器件，将其实际再现光斑与计算点列图进行比较。构造透射体全息片的物光为离轴的球面波，始于轴外点Ａ（０，１３２ｓｉｎ８°，－１３２ｃｏｓ８°），参考光为平面光束，其与Ｚ轴夹角为１７°。激光器采用氩离子激光器（Ｓｐｅｃｔｒａ－ｐｈｙｓｉｃｓＭｏｄｅｌ２０２０），波长４８８ｎｍ；干板感光胶为重铬酸明胶（ＤＣＧ），胶层厚为１５μｍ；通光口径３０ｎｍ。测试时把全息片放在干板的位置。挡住物光，让再现光以和参考光路相同的路径平行入射到全息片上，在全息片后垂直光轴放置毛玻璃片，平行光轴移动毛玻璃片，可观察到－１级衍射光的变化。在距离原点的距离分别为（ａ）４０ｍｍ，（ｂ）７０ｍｍ，（ｃ）８７ｍｍ，（ｄ）９５ｍｍ的地方用ＣＣＤ拍摄了衍射光的形状，与程序计算的点列图在形状和大小上都吻合     

高阶模激光束通过会聚光学系统的聚焦特性

以惠更斯 -菲涅尔原理和取样理论为基础 ,利用计算机编程计算和绘图软件 Graftool得到高阶模激光束 (如厄米 -高斯光束 TEM1 1 、TEM1 2 (或 TEM2 1 )、TEM2 2 和拉盖尔 -高斯光束 TEM1 0 、TEM1 1 )经过会聚光学系统 (以双透镜聚焦系统为例 )传播后的聚焦曲线 (r- z)。在聚焦曲线上 ,r的极小值 rmin就是激光束会聚的聚焦光斑尺寸 ,对应的 z值是束腰位置 zfocus。这样就从理论上获得了上述激光束通过会聚光学系统后的束腰位置和聚焦光斑尺寸 ,从而为研究高阶模激光束的聚焦问题提供了一种新方法     

Complex ray representation of the astigmatic Gaussian beam propagation

The method of Gaussian beam ray-equivalent modelling, first proposed by Arnaud, is generalized to the case of general astigmatism. It has been shown that a generally astigmatic Gaussian beam can be properly represented by two complex rays, or equally by four real rays, which are treated by the well-known propagation equation and ray tracing method in geometric optics, and from which the beam parameters are easily obtained. Illustrative numerical examples are given. The equivalence between the complex-ray treatment and the generalized ABCD law is also shown.     

Principal surface wave velocities in the point focus acoustic materials signature V(z) of an anisotropic solid

This paper deals with the point focus beam (PFB) acoustic materials signature V(z) of an anisotropic solid, and in particular how it tends to be dominated by a limited number of principal surface rays. These rays are associated with propagation directions in which the Rayleigh wave (RW), pseudo-surface acoustic wave (PSAW) or a lateral wave slowness has an extremum. The phenomenon is interpreted in terms of the complex azimuthally averaged reflectance function of the surface, and also explained on the basis of a ray model. We illustrate the phenomenon with a number of examples, pertaining to the surfaces of single crystal copper and a carbon-fibre epoxy composite. In the case of copper, which has a much larger acoustic impedance than the water couplant, the oscillations in V(z) are dominated by principal RW and PSAW, whereas for the composite there is no RW or pseudo-SAW to be discerned with acoustic microscopy (AM), and V(z) is dominated by principal lateral waves. The utility of PFB AM in the study of anisotropic solids is further elaborated with examples showing how V(z) is sensitive to surface orientation, and how V(z) is affected by the presence of a surface over layer. The phenomena examined in this paper expand the scope for determining materials characteristics, such as elastic constants, crystallographic orientation, residual stress and over layer properties, from PFB V(z) measurements.     

面向HIRFL-CSR主动式点扫描技术的剂量标定方法研究(英文)

基于HIRFL-CSR肿瘤重离子治疗终端主动式束流配送系统发展了面向三维点扫描适形调强治疗技术的在线监测器点扫描剂量标定方法。为了验证点扫描剂量标定方法的稳定性和可靠性,利用HIRFL-CSR提供的C离子束考察了在线监测器剂量标定因子的能量依赖以及不同扫描步长的影响。结果表明:在线监测器剂量标定因子存在能量依赖;不同扫描步长对剂量标定因子影响较小（偏差小于1.8%）。证明了点扫描剂量标定方法的稳定性和可靠性。鉴于在三维点扫描适形调强治疗技术中影响在线监测器点扫描剂量标定因子的因素较多,建议今后续继续研究点扫描剂量标定因子影响因素,修正和完善点扫描剂量标定方法。As an important step of the application of spot scanning technique to heavy ion therapy, an experimental calibration procedure of online beam monitors based on standard of absorbed dose to water has recently been developed for scanned pencil like carbon ion beam in the deep seated tumor therapy terminal at the Heavy Ion Research Facility in Lanzhou (HIRFL). In this work, creating homogeneous irradiation field with steerable spot beam was tested using a 207 MeV/u penci like carbon ion beam. Then the verification of energy dependence of the calibration factors (CFs) and the influence of scanning step on the CF were also shown, as a part of the heavy ion clinic dosimetry researches. The results showd that the monitor CF presented energy dependence and performed stable response with deviation of 1.8% for the variation of scan steps. In this paper, the suitability and effectiveness of beam monitor calibration procedure for dynamic particle beam delivery were verified and the further research points to improve the calibration procedure were suggested.     

A sound ray tracing algorithm in three-dimensional heterogeneous media based on wavefront traveltimes interpolation

A kind of three-dimensional（3-D） sound ray tracing algorithm in heterogeneous media is studied. This algorithm includes two steps： the first step computes the wavefront traveltimes forward; the second step traces the sound rays backward. In the first step, the computation of wavefront traveltimes at discrete grid points from the sound source, was found on Eikonal equation solutions and carried out by GMM （Group marching method） wavefront marching method based on level set. In the second step, sound ray tracing was proceeded gradually from the receiver to each cell towards the sound source, with wavefront traveltimes computed in the first step. Time values on arbitrary positions in each cuboid cell can be expressed by linear interpolation of wavefront traveltimes at the same cell＇s grid points. Thus, an algorithm of 3-D sound ray tracing in heterogeneous media is put forward. The simulation results indicate that this method can improve both the accuracy and the efficiency of 3-D sound ray tracing greatly.     

Generation of an axially super-resolved quasi-spherical focal spot using an amplitude-modulated radially polarized beam

An axially super-resolved quasi-spherical focal spot can be generated by focusing an amplitude-modulated radially polarized beam through a high numerical aperture objective. A method based on the unique depolarization properties of a circular focus is proposed to design the amplitude modulation. The generated focal spot shows a ratio of x:y:z=1:1:1.48 for the normalized FWHM in three dimensions, compared to that of x:y:z=1:0.74:1.72 under linear polarization (in the x direction) illumination. Moreover, the focusable light efficiency of the designed amplitude-modulated beam is 65%, which is more than 3 times higher than the optimized case under linear polarization and thus make the amplitude-modulated radial polarization beam more suitable for a wide range of applications.     

基于光的反射与折射定律的表述方法推导及应用

光的反射和光的折射是几何光学应用中最基本的方法。在现代精密光学元件加工过程中,其不同的表述方法可以为光线追迹、棱镜误差分析以及棱镜装调提供不同的解决思路。介绍了光的反射定律和折射定律的传统形式表述方法,并推导了光的反射定律和折射定律的矢量、矩阵及四元数3种表述方法。通过Matlab辅助下的模拟计算,得到施密特棱镜检验光路中2个不同区域入射光线的反射在水平方向上对称分布于前表面反射像两侧,与实际应用相符,实现了矢量、矩阵和四元数表述方法在施密特棱镜检验光路中的应用。3种表述方法可以为光线追迹、棱镜误差分析以及棱镜装调提供科学、实用的解决方法。     

高能激光光束质量β因子的影响因素分析

采用二维线性调频z变换算法,分析了影响高能激光系统光束质量β因子测量准确性的因素。本文详细分析了采样点数(即衍射极限内的采样点数)和衍射光斑图像的能量损失率对光束质量β因子的影响。在衍射极限角直径2(λ/D)范围内不同采样点数的模拟结果表明:采样点数越高,光斑衍射图像的分辨率越高,进而光束质量β因子计算越准确。在一倍衍射极限角2.44(λ/D)范围内应最低不少于10个采样点,即可将β因子的测量误差控制在3%。同时,不同像差对光斑图像能量损失率的敏感程度不同,相同能量损失率下,高阶像差的β因子测量误差要高于低阶像差。特别是球差类的像差对能量损失最为敏感,约5%的能量损失就可带来15%~30%的β因子计算误差。     

Identification of radiative properties of reticulated ceramic porous inert media using ray tracing technique

The radiative properties of reticulated porous inert media are computationally identified using the real three-dimensional structural data of porous media. The computational grids data are reconstructed from three-dimensional computer tomography scans and magnetic resonance image scans of different reticulated porous media. A ray tracing algorithm is used to track the rays inside the grid structure. Statistically large numbers of rays are traced for their path length and incident angle, which are used to find the probability based equivalent extinction coefficient and scattering phase function. The equivalent extinction coefficients are found for porous media with different porosities and pore densities. The dependency of specular and diffuse scattering phase functions on the porous structure and surface reflectance are also studied.     

Flat-top beam profile generated using a fiber-bundle prism-coupled beam shaper

In this paper, an optical beam shaping system is theoretically and experimentally investigated. The optical system design software ZEMAX is used to simulate and analyze the reported beam shaping design. By using this software ray tracing diagrams are presented with the aim of studying the direct beam propagation, total reflection rays, and the lost rays. The prism duct output beam shape and radiance profiles in both position space and angle space are also studied. For experimental investigation, a two-stage beam shaping design including a fiber-bundle and a prism duct is used. A source light is used for the fiber-bundle illumination and the photograph image of the output beam is taken by a digital camera. The fiber-bundle output beam cross section is a rectangular shape with a dimension of 25.65 mm width and 2.44 mm height. In another experiment, the prism output beam is captured by a CCD camera. The prism output beam shape depends on the prism exit face, which is a rectangle (4.15 mm × 3.55 mm) for this case. The image date of the prism output beam is converted to a response curve, which is approximately a flat-top profile. The experimental image profiles are compared with the simulated image profiles and there is a good agreement between the observed results.     

Pulse propagation in optical fibres with index profiles slowly varying along their length

This paper describes the formalism for calculating the effect of profile variations along the fibre on transit times and path parameters for rays in multimode fibres. The ideal case of power-law profiles is considered in detail and it is shown that when the exponentq is given byq=q ₀+f (z), the fibre may be described by an equivalent exponentq _e. Simple formulae forq _e in terms of the average properties off(z) are given. The ray parameter varies and this is shown to have only a minor effect on transit time, but does imply that some rays suffer an attenuation when0. If the amount of dopant in any crosssection is assumed constant, the fibre radius must vary whenq varies and profiles with this attribute are examined and shown to have ray behaviour similar to that described above.     

Propagation of supercontinuum laser sources in a slant path through the atmosphere

Taking the atmospheric refraction, extinction and turbulence into account, the propagation characteristic of supercontinuum laser sources in a slant path through the turbulent atmosphere is investigated. The effect of spectral width, initial spot size and zenith angle in a slant path on the beam width and propagation efficiency are studied in details. Numerical examples reveal that the beam width and propagation efficiency are different values while the spectral width varies. With the zenith angle in a slant atmospheric path increasing, the beam width of supercontinuum laser sources will increase and propagation efficiency will decrease. The initial spot size has an optimal value when spectral width and zenith angle are fixed.     

轴棱锥-透镜系统产生局域空心光束中心亮斑的消除

本文提出利用相位调制的新方法, 在光路中插入螺旋相位板, 使句域空心光束(Bottle beam)中心变为相位奇点, 在使用轴棱锥-透镜系统产生局域空心光束(Bottle beam)时, 消除了衍射等因素导致Bottle beam内部的轴上光强, 这利于用Bottle beam构建空心光镊系统. 理论分析及数值模拟与实验结果很好地吻合.     

Spatial correlation of the sound field in an ocean shelf zone

The spatial correlation of explosive signals received by hydrophones lying on the bottom of a shelf zone is studied as a function of the length of the propagation path. The correlation coefficient is found to exhibit quasi-periodic variations with increasing distance to the explosive source of sound. It is shown that the value of the correlation coefficient noticeably increases and its periodic variations practically disappear when the measurements are performed for the signals arriving by individual rays or narrow ray bundles. The low efficiency of a linear horizontal receiving array is pointed out.     

机械刻划光栅的光线追迹方法

为了评价光栅的光谱质量,完成所设计光栅的光线追迹,针对机械刻划光栅的光线追迹提出了一种改进方法.在费马原理的基础上利用光程函数法得到入射光通过光栅后的光谱分布情况,再使用传输矩阵的计算方法构造出光谱的点列图.该方法适用于刻划在平面、球面和非球面基坯上的等间距和变间距光栅,光栅的光谱面可以为平面或者二次曲面. 通过刻划在非球面基坯上的凹面光栅验证了光线追迹方法的可靠性.     

神龙二号热阴极注入器束流调试

神龙二号注入器是一台感应叠加型强流脉冲电子束源,采用热阴极工作模式,为神龙二号加速器提供间隔可调的三脉冲电子束。该注入器的束流调试采取PIC模拟和实验调试交互验证、互相促进的方式,先是通过束斑测量确定引导线圈磁场的加载范围,然后通过PIC方法逐级梳理阳极段束线各线圈的磁场配置,再通过束斑测量加以确认。通过这种束流调试方法,获得了保持束流脉冲平顶完整通过的三种磁场配置,以适应下游加速段束流传输的不同要求。讨论了影响束流调试效果的因素,认为提升神龙二号注入器性能的关键是进一步改进大面积热阴极发射的均匀性。     

A unique approach to accurately measure thickness in thick multilayers

X‐ray optics called multilayer Laue lenses (MLLs) provide a promising path to focusing hard X‐rays with high focusing efficiency at a resolution between 5 nm and 20 nm. MLLs consist of thousands of depth‐graded thin layers. The thickness of each layer obeys the linear zone plate law. X‐ray beamline tests have been performed on magnetron sputter‐deposited WSi₂/Si MLLs at the Advanced Photon Source/Center for Nanoscale Materials 26‐ID nanoprobe beamline. However, it is still very challenging to accurately grow each layer at the designed thickness during deposition; errors introduced during thickness measurements of thousands of layers lead to inaccurate MLL structures. Here, a new metrology approach that can accurately measure thickness by introducing regular marks on the cross section of thousands of layers using a focused ion beam is reported. This new measurement method is compared with a previous method. More accurate results are obtained using the new measurement approach.     

General Geometric Optics Formalism in Plasmas

This paper exploits a general approach to geometric optics in inhomogeneous plasmas based on the properties of the local dielectric tensor ?. We express ? in terms of its eigenvalues ?j and eigenvectors ?. Then to zeroth order in the geometric optics approximation the determinant D = ?1?2?3 vanishes and the elements ?j vanish separately in pairs or simultaneously. It is shown that this branching in the dispersion relation changes the formulation of the geometric optics equations. The ray tracing and the transport of the amplitude of the wave in both degenerate and nondegenerate cases is described. The general procedure for transition through a boundary between degenerate and nondegenerate regions, where the rays split into two parts each following a different branch of the dispersion relation is also presented in this paper. We demonstrate our general method in a case, where radiation from a vacuum region enters an inhomogeneous magnetized plasma layer.     

Submicrometer hard X‐ray focusing using a single‐bounce ellipsoidal capillary combined with a Fresnel zone plate

A single‐bounce capillary with an ellipsoidal shape has been used for two‐step focusing in combination with a Fresnel zone plate (FZP). The FZP serves as a first microfocusing element and produces a demagnified micrometer image of the source, before the elliptical capillary makes a last final compression of the beam. With 15 keV X‐rays from the European Synchrotron Radiation Facility BM5 bending magnet, the two‐step demagnification system produced a focus of about 250 nm with a gain of more than 1000. The use of an ellipsoidal capillary as a micro‐mirror under off‐axis illumination using micro‐prefocusing optics might open up new opportunities in nanofocusing developments.