Effective method of calculating fields in optical cavities with cylindrical symmetry and shaded axial zone

It is proposed to calculate (in the diffraction approximation) fields in optical cavities with shaded axial zone and large mirror aperture, in a cylindrical coordinate frame, using a new algorithm based on the use of the stationaryphase method. Unlike the already known ones, the method has high efficiency in the region of large Fresnel numbers, and is close in speed to the method of fast Fourier transformation. The procedure is described and specific calculation results that illustrate the proposed method are presented.Translated from Preprint FIAN 121, Lebedev Physics Institute, Moscow, 1990.     

Self-consistent field method and non-self-consistent field method for calculating the positron lifetime

Many methods are used to calculate the positron lifetime,these methods could be divided into two main types.The first method is atomic superposition approximation method and the second one is the so called energy band calculation method.They are also known as the non-self-consistent field method and self-consistent field method respectively.In this paper,we first introduce the two basic methods and then,we take Si as an example and give our calculation results,these results coincide with our latest experimental results,finally,we discuss the advantages and disadvantages of the two methods.     

Comparison of methods for calculating the sound field due to a rotating monopole

A spherical harmonic expansion for the sound field due to a rotating oscillating point source has recently been derived. This paper provides further confirmation of the expansion results by comparing it with two known numerical approaches to determining the sound field. In the advanced time approach-applicable for Mach numbers below 1-the sound at transmission time determines the field at an observation point from the distance from source to observation point at the transmission time. In the retarded time approach the field at the observation point at the observation time is determined by solving for the retarded transmission times. The results from all three approaches are shown to be in good agreement. Expressions for the far-field instantaneous frequency are also derived and shown to agree with previous work.     

复杂腔体本征电磁场空间分布的统计方法

利用半经典近似方法分析了电大复杂腔体内电磁波传播的混沌特征,从而引入了3维矢量本征函数的随机平面波假设。根据电磁波传播的随机极化特征,利用统计方法推导出基于该假设本征电磁场空间分布的统计模型。应用数值方法对3维Sinai微波腔体进行模拟计算,其计算结果与统计模型符合较好。这些统计模型与腔体的具体细节特征无关。     

偏心光学系统的中心点亮度的计算

本文讨论了偏心光学系统的中心点亮度计算中所必须考虑的离焦、波差展开式、数值计算等几个主要问题。     

复杂腔体本征电磁场空间分布的统计方法

 利用半经典近似方法分析了电大复杂腔体内电磁波传播的混沌特征,从而引入了3维矢量本征函数的随机平面波假设。根据电磁波传播的随机极化特征,利用统计方法推导出基于该假设本征电磁场空间分布的统计模型。应用数值方法对3维Sinai微波腔体进行模拟计算,其计算结果与统计模型符合较好。这些统计模型与腔体的具体细节特征无关。     

An analytical method for the calculation of the aberrations of optical systems

Based on the exact expression for the angular eikonal of a second-order surface, an analytical method for the analysis of the aberrations of an optical system is constructed and the principles for the optimization of such a system are formulated. Examples of the analysis and optimization of a single surface are given. The theoretical method developed is supported by the results of modeling of the caustic and the focal set in the image space of a point of a spherical refracting surface. The method constructed is exact and does not require using programs for tracing rays through the system.     

Improved calculation of field isotope shift constants for optical spectral lines

Following the approach of previous investigations improved formulae for the field isotope shift constantC _unif of optical spectral lines have been derived assuming a uniform nuclear charge distribution. From these formulaeC _unif may be evaluated forselectrons with an accuracy of better than 1%. After considering the effect of the different normalization procedures the results obtained by different methods of approach are in good agreement.     

Application of the elongation method to nonlinear optical properties: finite field approach for calculating static electric (hyper)polarizabilities

A novel finite-field approach for calculating electric (hyper)polarizabilities based on the elongation method is developed. The method was tested at the semi-empirical PM3 level by using three model systems: the hydrogen chain, the water chain and polyacetylene. The results satisfactorily reproduce the ‘exact’ MOPAC values. The most important advantage of this approach is the large saving of computer time since the dimension of the SCF equation remains the same regardless of the number of atoms in the system. Thus, it is a very useful tool to treat large systems. The method can also be applied to building up a chain containing an arbitrary sequence of monomers.     

超音速化学氧碘激光器内流动与光能提取耦合仿真

针对超音速化学氧碘激光器,实现了包含化学反应的超音速流场和光场的耦合仿真。完善了流体力学计算与波动光学计算的耦合方法,解决了耦合计算中各物理参量有效传递及收敛判据选取等问题,根据具体的激光器参数,完成了耦合仿真。耦合计算体现了腔内光场与包含化学反应的超音速流场相互作用的机制,能够反映出有源腔中振荡光场的衍射和光能提取对流场所带来的影响,计算结果包含激光器流动过程、化学过程及光学过程的诸多工作参量。     

超音速化学氧碘激光器内流动与光能提取耦合仿真

 针对超音速化学氧碘激光器,实现了包含化学反应的超音速流场和光场的耦合仿真。完善了流体力学计算与波动光学计算的耦合方法,解决了耦合计算中各物理参量有效传递及收敛判据选取等问题,根据具体的激光器参数,完成了耦合仿真。耦合计算体现了腔内光场与包含化学反应的超音速流场相互作用的机制,能够反映出有源腔中振荡光场的衍射和光能提取对流场所带来的影响,计算结果包含激光器流动过程、化学过程及光学过程的诸多工作参量。     

New method for calculating the spectra and radiation losses of leaky waves in multilayer optical waveguides

The efficiency of a new method for calculating the spectrum and attenuation coefficient of leaky electromagnetic modes is demonstrated with multilayer planar optical waveguides the guiding properties of which are determined by antiresonant reflection from the multilayer cladding (antiresonant reflecting optical waveguides) rather than by total internal reflection from the core-cladding interface as in standard optical waveguides. The new method applies to calculation of both electromagnetic modes in dielectric waveguides and electron quantum states in multibarrier semiconductor heterostructures. The characteristics of multilayer waveguides calculated by the new method are compared with published data obtained from a complex dispersion relation by the transfer matrix method. As an example, the wavelength dependence of the radiation losses for the first TE mode of a planar optical waveguide containing 52 pairs of layers is calculated.     

小尺度封闭空间声场的无网格数值算法

无网格法是一种新兴的数值计算方法,具有不需要网格支持的特点。本文将该方法引入室内声学建模,推导了无网格声场数值计算模型,并将其应用于典型小尺度封闭空间内部声场的数值分析。针对声传递函数,将本方法与理论解和SYSNOISE计算结果进行了比较,并将计算的混响时间与实验测量结果作了对比,表明本方法具有良好的精度。     

轴对称非静态电流分布轴外场的一种计算方法

在轴对称非静态电流分布的情况下,利用麦克斯韦方程组和轴对称性,给出了轴外电磁场的一种计算方法.     

Tailoring the chemical reactivity and optical properties of clusters by size, structures and lasers

We present results of theoretical investigations in three areas. I. Reactivity of anionic noble metal oxide clusters (Ag, Au) relevant for catalyst design: It will be shown that the cooperative effects are needed to activate clusters in order to invoke strongly size selective reactions with O₂ and CO. These results obtained with DFT method elucidated fully experimental findings. II. Stationary optical properties of silver clusters: ab initio results on absorption spectra of small silver clusters and on geometric relaxation of their excited states leading to the observed fluorescence are presented and compared with experimental data. III. Real-time investigation of ultrafast processes and their control by tailored laser fields: nonstoichiometric Na_nF_n-1 clusters are suitable prototypes to study dynamics in excited electronic states. For this purpose we use our combination of the Wigner distribution method and MD “on the fly” allowing to treat all degrees of freedom. Analysis of simulated pump-probe signals will be shown for Na₂F for which experimental data are available. Pump-dump control of the photoisomerization in Na₃F₂ avoiding conical intersection will be presented using our new strategy for obtaining tailored laser fields based on the intermediate target in excited state which (if available) guarantees the controllability in the complex systems.     

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。