平面透射光栅的菲涅耳衍射

从标量场的菲涅耳衍射理论出发,研究了球面波入射平面透射光栅的衍射场,导出菲涅耳衍射场的复振幅分布,并得到光栅菲涅耳衍射角的计算公式．结果表明,在理想情况下菲涅耳衍射的每一级衍射波都是一个球面波;在对菲涅耳衍射角进行新的定义后,衍射角的计算仍然可以采用夫琅禾费衍射的光栅方程．     

菲涅耳单缝衍射动态演示实验

通过设计简单扩束系统获得近似匀强球面波,并利用计算机技术,开发出一个可以动态显示菲涅耳单缝衍射光强分布的演示实验。     

如何划分菲涅耳衍射和夫琅和费衍射

在讨论光的衍射时,一般总是把它分为菲涅耳衍射和夫琅和费衍射、但如何划分?根据是什么?这问题看法很不统一.在一般经典的光学著作中都是以所取的近似程度来划分的,而目前在一些现代光学的书中却划分得比较简单,提出了近场衍射即菲涅耳衍射和远场衍射即夫琅和费衍射的概念. 关于光在平面屏幕上的衍射问题早在1882年就由基尔霍夫得出了菲涅耳-基尔霍夫衍射公式式中U(P)为光在P(x,y)处的复振幅分布.∑为衍射孔,r0表示点光源P0(x0,y0)到孔上P1(xl,y1)点的距离,r表示观察点P到P1处的距离n为衍射孔的外法线. 后来索末菲又于1896年,首次给出了…     

光学系统中的光栅衍射自成像现象:广义的Talbot效应

本文基于菲涅耳-克希霍夫(Fresnel-Kirchhoff)积分推导了在菲涅耳(Fresnel)近似下,光栅在光学系统中的衍射自成像现象:广义的Talbot效应。并把几何成像归结为Talbot成像的一个特殊情况。依据广义Talbot公式,讨论了在平行光、球面波照明时,光栅的衍射自成像特点。最后,用干涉观点解释了光学系统中的衍射自成像现象。     

菲涅耳数字全息成像系统的脉冲响应分析

数字全息成像由CCD记录数字全息图后经过计算机数值重建物光波场,这个过程从傅里叶变换角度看等同于数字全息图的频谱分析。讨论了数字成像系统的脉冲响应函数,并分别推导了其实像、虚像、零级像在平面波和球面波照射下的波前复振幅分布。结果表明,实像和虚像是移位的夫琅和费衍射分布,而零级像是CCD光瞳的菲涅耳衍射分布,且与参考光波前分布无关。     

菲涅耳-基尔霍夫积分与半波带法分析衍射光谱

惠更斯菲 涅耳原理指出光的衍射本质是无穷多次波的相干叠加.在研究衍射光谱的强度时可使用菲涅耳-基尔霍夫衍射积分进行计算,但该积分的计算较为复杂.为了简化计算而引入菲涅耳半波带的概念,把积分运算简化为振幅矢量的叠加,从而在研究衍射时由菲涅耳-基尔霍夫衍射积分过渡到菲涅耳半波带法.在菲涅耳半波带法中波前上相邻两个半波带到达叠加点的光程差为半个波长,从而导致相位差π.因此相邻两个半波带引起的振动在叠加点发生相消,最终叠加点的光强由发出次波的半波带数目的奇偶性决定.奇数个半波带在叠加点的光强得到加强,偶数个半波带在叠加点的光强发生相消.     

光学系统像点附近的光强空间分布

根据准确的菲涅耳衍射振幅和光强解析表达式推导出光学系统像点队近的光强空间分布。与采用洛梅尔函数计算不同,文中使用常用的贝塞尔函数准确地计算了光强空间分布,从而使计算更容易、结果更直观。并对菲涅耳数这一物理概念进行了论述。     

高斯光束菲涅耳圆孔衍射轴上的光强分布

本文从惠更斯－菲涅耳原理的数学表达式出发，在菲涅耳圆孔衍射的情况下求出了高斯光束入射时轴上光强分布的解析表达式，并对比平面波和球面波入射的情况进行了分折讨论．     

用菲涅耳半波带法计算屏障的声插入损失

本文以惠更斯-菲涅耳衍射原理为基础,运用菲涅耳半波带叠加的概念,给出了在一半无限大薄屏后球面波的衍射声场中接收点的声压幅值的近似表达式,并推广至声屏障为一尖劈或一个三边厚障板的情况,得到了屏障声插入损失的一种新的计算方法,称为菲涅耳半波带法。理论计算值与实验结果符合较好,表明该方法可应用于噪声控制工程中。     

物理光学 其他

O436 2005053267 会聚球面波通过环形光阑的光强分布=Intensity distribu- tion of converging spherical waves passing through an an- nular aperture[刊,中]／刘波(西南交通大学应用物理系． 四川,成都(610031)),吕百达∥激光技术．-2005,29 (1)．-77-79,93 基于菲涅耳衍射积分公式,推导出了会聚球面波通过 环形光阑后场分布的解析公式,并讨论了一些特殊情况。 数值计算例表明,光强分布与菲涅耳数和遮拦比有关。使 用轴上光强公式和近似公式对焦移计算结果的比较,证明 了近似公式的适用范围。图4参5(杨妹清)     

Modeling of Multiple Scattering from an Ensemble of Spheres in a Laser Beam

This paper details the results of upgrading an effective numerical technique (derived for multiple-scattering simulations in photon correlation/cross-correlation with a plane-wave light source) for the modeling of multiple scattering in a laser beam. The off-axis shape coefficients of an arbitrary beam are computed starting from the set of known beam-shape coefficients for an on-axis location by using the addition theorem for the spherical vector wavefunctions of the first kind. The discussed technique is verified by comparison with a localized approximation for a focused Gaussian beam and with Barton's spheres-arbitrary beam interaction theory. An additional advantage of the proposed technique (self-testing of the computation accuracy by comparison of the off-axis beam-shape coefficients evaluated from two different on-axis origins) is demonstrated.     

Acoustic field of a point source in water with air bubbles

A model problem of sound wave propagation from a point source located in water at the center of a spherical bubble cloud is solved. The resulting dependences of wave attenuation on the sound frequency and bubble concentration are compared with those obtained in the approximation of a quasi-homogeneous medium. The validity limits of this approximation are determined.     

Laguerre-Gaussian beam scintillation on slant paths

Scintillation evaluations for Laguerre-Gaussian (LG) beams for slant paths are made using Rytov approximation. On- and off-axis scintillation is formulated and calculated up to several tens of kilometers of slant distances for different zenith angles. Scintillation index variations against radial receiver point and different source sizes are also investigated. In all cases evaluated, it is found that LG beams with higher radial mode numbers result in less scintillation than Gaussian beam. Kolmogorov spectrum function is utilized in the scintillation calculations.     

Stationary electromagnetic fields around black holes

In the framework of the Newman-Penrose formalism the electromagnetic field of a general stationary source occurring in the vicinity of a Schwarzschild black hole is obtained in the test-field approximation. The field is expressed in terms of hypergeometric functions (radial parts) and spin-s spherical harmonics (angular parts) both outside and inside the radius at which the source is, located. As examples, the fields of point charges, charged rings, current loops and magnetic dipoles (generally located in non-axisymmetric positions) are calculated.     

棱镜分光光谱仪的光学系统设计与光谱特性计算

设计了离轴全球面成像光谱仪和离轴校正透镜棱镜分光成像光谱仪两种光学系统.在离轴全球面成像光谱仪的基础上,提出了改进型离轴校正透镜光谱仪,仅采用一个色散棱镜,避免了大口径同心透镜;有效校正了大视场像差,色散非线性修正效果显著.通过调节离轴角和光谱仪的焦距控制了畸变,补偿了与波长相关的狭缝弯曲,减小了残余像差,并降低了整个光谱仪工程实施的难度.从工程合理性、加工可实现性和光学性能等方面比较了两个系统的特点,推导和给出了光谱分辨率和狭缝弯曲的计算结果.从设计结果看,改进型离轴校正透镜光谱仪的传递函数最小值大于75％,而离轴全球面成像光谱仪的最小值只大于60％.从加工难易程度看,离轴全球面成像光谱仪采用一个接近Φ200 mm的石英透镜,其透射材料远不如改进型离轴校正透镜光谱仪透镜材料的均匀性和面形准确度高,而且大口径透镜大大增加了制备难度和成本.从工程布局看,改进型离轴校正透镜光谱仪充分考虑了与机械结构的匹配,狭缝与第一面反射镜的轴向距离较合理.从光谱特性看,两个光学系统的光谱分辨率结果基本接近,离轴全球面成像光谱仪光谱弯曲结果略好于离轴校正透镜结构.因此,综合比较得出离轴校正透镜光谱仪是最佳的选择方案,该系统可应用在短波红外波段的光谱成像的遥感探测.     

Quantitative measurement of large-aperture aspheric surfaces by off-axis Ronchi test

An off-axis Ronchi test based on the phase-shifting technique is presented to measure the aspheric mirror quantitatively. In this paper, slopes of deviations from the mirror's ideal aspheric shape are derived when an off-axis point source is used. By integrating these slopes, the deviations of the shape are obtained and then the tested shape can be reconstructed. Compared with the coaxial Ronchi test, the measurement error caused by combination fringes can be avoided, and this system is more flexible. In the experiment, a marked point is used to guide the phase unwrapping procedure, which improves the accuracy of extracting corresponding phase points. In addition, the method has strong anti-noise ability. The validity of the method has been verified by both computer simulations and a preliminary experiment.     

离轴球形粒子对高斯波束的散射光通量的计算

利用矢量球谐函数展开的方法,研究了离轴球形粒子对椭圆高斯波束的散射。根据其远区散射场的形式,得出了归一化散射场的斯托克斯参量(散射强度)与颗粒直径、折射率以及散射角的关系。建立了计算离轴球形粒子对高斯波束散射通量的解析模型,计算了散射光在任意散射方向上的光通量,得到了前向任意立体角内散射通量的计算公式,为激光散射探测提供了理论依据。     

Three-dimensional locating of paraxial point source with axicon

This Letter presents a theoretical and experimental study of an axicon illuminated by an off-axis paraxial point source. The Fresnel diffraction integral is applied to show that a paraxial point source produces a Bessel beam. A simple analytical relationship is demonstrated between the location of the point source and the spatial frequency and the center of the resulting Bessel beam in the image plane of a camera. Finally, experimental verification is given by translating a point source of light along the optical axis of an axicon and comparing the resulting predicted and recorded beam intensity profiles. The resulting images are then analyzed to predict the location of the point source with excellent accuracy.     

Comparison between radiative transfer theory and the simplified spherical harmonics approximation for a semi-infinite geometry

In this study, the third-order simplified spherical harmonics equations (SP3), an approximation of the radiative transfer equation, are solved for a semi-infinite geometry considering the exact simplified spherical harmonics boundary conditions. The obtained Green's function is compared to radiative transfer calculations and the diffusion theory. In general, it is shown that the SP3 equations provide better results than the diffusion approximation in media with high absorption coefficient values but no improvement is found for small distances to the source.     

Scintillations of multiwavelength Gaussian, cos, cosh and annular Gaussian beams

We provide the scintillation formulation for a multiwavelength source. Within this context, the scintillation aspects of Gaussian, cos, cosh and annular Gaussian beams are investigated. For all situations examined, it is found that for a source comprising many wavelengths, there will be less scintillations as compared to a single wavelength source of the lowest wavelength and but the reverse will be true if the comparison is with respect to the single wavelength source of the highest wavelength. The same is observed at all propagation distances, source sizes, on-axis and off-axis positions considered. Additionally, it is seen that the scintillation characteristics of multiwavelength sources will follow similar trends of single wavelength sources. The analysis is based on the Rytov approximation, therefore our results are valid for conditions of weak atmospheric turbulence.