电多极矩跃迁选择定则的对称分析

只有由群的对称性才可能导出每个不可约表示的对称性波函数, 即对称化基函数.也只有由群的对称性才可能导出电子状态跃迁的最一般选择定则 , 即电偶极跃迁E1, 电四极跃迁E2 和 电八极跃迁E3跃迁的选择原则. 本文以 和 为例, 导出电多积跃迁的选择原则. 角动量的选择定则只是特例. 并用方法SAC-CI/6-31G 计算了 H2O和 CC的基态以及其激发态的激发能和振子强度.本文只适合单光子过程. 计算都与理论相合.     

关于总轨道量子数L的选择定则

多电子原子的电偶极跃迁,不外乎两种情况:其中只有一个电子发生跃迁;或者有两个或两个以上电子同时跃迁.对于总轨道量子数L的选择定则,前者是否△l=±1,后者是△l=0,±1.对于△l=0,±1情况,有的教师存有争议,对此本文给予简单讨论. 关于电偶极辐射,存在一普遍、严格的选择定则,对多电子原子可归纳为两点: 1.原子总电子波函数的宇称必须改变:奇到偶或偶到奇. 2.总电子波函数为各电子波函数的乘积.由于各电子波函数的宇称由该电子的轨道量子数li的奇偶性表征(即(-1)li),故总电子波函数宇称的奇偶性取决于所有电子的轨道量子数之和if.的奇偶性…     

空间群选择定则的计算方法

一、引 言 晶体空间群选择定则是用群论方法研究光与晶体相互作用(例如红外吸收、γ散射等过程)的一个基础工作.在晶体特别是在半导体中,跃迁和散射过程涉及电子和声子、电子和光子以及电子同时和声子及光子的相互作用.例如,在锗、硅等半导体中的光跃迁就包括没有声子参加的直接光跃迁和有声子参加的间接光跃迁.只允许某些跃迁的规则称为选择定则, 由量子力学我们知道,由算符H描述的相互作用引起电子从φm态跃迁到φn态,跃迁几率的大小,由下面的积分决定:当这个积分为0时,跃迁是不允许的;当这个积分不为0时,跃迁是允许的.但这个积分计算起…     

H2O和HLi分子的双光子激发

用全相对论量子力学计算H2O和HLi的双光子偶极激发。为对比起见,同时用非相对论的对称匹配团族-组态相互作用法(SAC-CI)计算其单光子激发。对于无对称中心的H2O和HLi,符合相应群的对称选择原则。双光子跃迁几率一般比单光子跃迁的小3～5个数量级。在计算双光子偶极激发时,应采用同时包含了空间的对称性和时间反转对称性的全相对论。     

PrP_5O_(14)晶体中Pr~(3+)离子的f-d辐射跃迁

本文讨论了计算稀土离子4f~(N-1)5d-f~N辐射跃迁几率的一般方法,提出了这类跃迁的亲态选择定则。并在C_(2v)群对称下,具体计算了Pr~(3+)离子在PrP_5O_(14)晶体中的f-d辐射跃迁几率,结果指出稀土离子的f-d跃迁几率比f-f跃迁几率大得多。     

群论在发光光谱学中的应用

在本文的第一部分里,概述了晶体发光学中常用对称群的特征标表,给定了能级的劈裂以及电偶极和磁偶极跃迁的选择定则。立方体群O_h和四面体群T_d至今仍很重要。近年来,人们发现一些低对称性的群越来越显得重要了,特别是对于稀土离子激活的材料。在第二部分里给出了一些例子:主要是ZnS中的Cu~(2+),还有ZnS中的Ni~+,最近已发现它是和Cu~(2+)等电子的;掺入ZnS,ZnSe和很多其它发光材料中的Mn~(2+)以及稀土离子Ce~(3+)、Yb~(3+)和Eu~(3+)的发光。     

群论在发光光谱学中的应用

在本文的第一部分里,概述了晶体发光学中常用对称群的特征标表,给定了能级的劈裂以及电偶极和磁偶极跃迁的选择定则。立方体群O_h和四面体群T_d至今仍很重要。近年来,人们发现一些低对称性的群越来越显得重要了,特别是对于稀土离子激活的材料。在第二部分里给出了一些例子:主要是ZnS中的Cu~(2+),还有ZnS中的Ni~+,最近已发现它是和Cu~(2+)等电子的;掺入ZnS,ZnSe和很多其它发光材料中的Mn~(2+)以及稀土离子Ce~(3+)、Yb~(3+)和Eu~(3+)的发光。     

H2X(X=O,S,Se,Te)分子的双光子激发

本文采用全相对论量子力学计算了H₂X (X=O, S, Se, Te) 分子的双光子过程, 并考虑相对论效应对双光子过程的影响. 结果表明, 各个不可约表示对称态下激发能有着明显的差异,它反应了双光子吸收过程中选择能级的特点. 同时, 采用非相对论的对称匹配簇/组态相互作用方法 (SAC-CI) 计算其分子的单光子激发, 并与之比较. 双光子跃迁概率要比单光子跃迁概率小2–5个数量级; 同一主族, 随着原子序数的增加, 相对论效应对分子体系的激发能量、跃迁概率、振子强度的大小都有显著地影响; 除此之外,每个分子遵守分子对称群的选择原则. 本文中, 分子H₂X (X=O, S, Se, Te) 的个别不可约表示对称态的跃迁矩分量和振子强度远远大于其他对称态下的跃迁矩分量和振子强度, 甚至大于单光子激发. 这不仅与分子的对称性有一定的关系, 而且应该是选择双光子跃迁能级的重要依据. 关键词： 全相对论量子力学 双光子激发 电偶极跃迁矩 振子强度     

基础课量纲分析法教学举例(下)

例9　原子激发态的平均寿命r 原子由高能级跃迁到低能级,放出一个光子,其能量ω等于跃迁前后两能级之差。ω接近于电子的轨道角频率ω0,作为数量级估计,可取ω0～ω。跃迁是一个量子力学过程,但性质类似于电动力学中的电磁辐射问题。 原子的光学跃迁通常表现为电偶极(E1型)跃迁,其寿命较短。如电偶极跃迁被量子数的选择定则禁止,则跃迁表现为磁偶极 (M1)型或电四极(E2)型,等等。平均寿命r的数量级可以估计如下: E1型如取-ea,a为原子半径则例如,相当于可见光谱的原子跃迁,如取求得Ml型多极数更高的跃迁可以从此类推,马十l型和MI型跃迁的平…     

fN组态的电偶极跃迁

本文考虑了晶体的对称性和奇、偶次晶场项对fN组态电植极跃迁的影响.引进一个新的波函数,计算了晶体中稀土掺杂离子fN组态能级间电偶极跃迁的矩阵元表达式.讨论和解释了J1=0→J2=0的跃迁,并和Judd公式进行了比较讨论.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.