二次型复折射率介质中的光导现象

本文讨论了n(z,r)=n_0(z)+n_2(z)r~2/r_e~2型复折射率介质中的激光传输问题,给出了激光传输参数(光束半径和波阵面曲率)的演化公式。指出只要存在一定大小的n_(21),在传输过一段特征距离z_c之后,将出现完全光导(即自相似模的传播),而且自相似模是激光体系的特征模式。其传输参数只与n_2有关,而与激光初始参数无关。自相似模必定是高斯球面波,而不是高斯平面波。     

Efficient generation of a photon pair in a bulk periodically poled potassium titanyl phosphate

In this report, we demonstrate the efficient generation of collinearly propagating photon pairs in a bulk periodically poled potassium titanyl phosphate pumped by a cw laser. The detected coincidence counts are more than 7400/s with 3.58 mW pump power in a Hanbury-Brown-Twiss-type experiment. The estimated photon pair production rate is about 0.73 MHz/mW. This is very promising for some applications, such as quantum key distribution, proof of the Bell-inequality, preparation of single photon states in broadband wave packets, Franson-type interference and so on.     

锕系核集体运动的负宇称态

从锕系区40多个核的正负宇称态的实验数据,如激发能、J^π、电偶极跃迁等,得到一系列与核结构有关的物理量,如宇称劈裂能级差δE_I,正负宇称带的第一和第二类转动惯量J⁽¹⁾和J⁽²⁾及第一负宇称态的电偶极跃迁强度比等,以及它们与角动量I或转动角频率ω的动力学和核子数A的系统行为,从而为研究锕系核负宇称态的产生机制及动力学特点提供了信息.     

Ab initio calculations of accurate dissociation energy and analytic potential energy function for the second excited state B1∏ of 7LiH

The reasonable dissociation limit of the second excited singlet state B¹∏ of ⁷LiH molecule is obtained. The accurate dissociation energy and equilibrium geometry of the B¹\Pi state are calculated using a symmetry-adapted-cluster configuration--interaction method in full active space. The whole potential energy curve for the B¹∏ state is obtained over the internuclear distance ranging from about 0.10nm to 0.54nm, and has a least-square fit to the analytic Murrell--Sorbie function form. The vertical excitation energy is calculated from the ground state to the B¹∏ state and compared with previous theoretical results. The equilibrium internuclear distance obtained by geometry optimization is found to be quite different from that obtained by single-point energy scanning under the same calculation condition. Based on the analytic potential energy function, the harmonic frequency value of the B¹∏ state is estimated. A comparison of the theoretical calculations of dissociation energies, equilibrium interatomic distances and the analytic potential energy function with those obtained by previous theoretical results clearly shows that the present work is more comprehensive and in better agreement with experiments than previous theories, thus it is an improvement on previous theories.     

浅谈物理教学改革的几点认识

围绕物理课程改革，中国物理学会前两届教学委员会曾举办过一系列研讨会，主题是基础物理教学的现代化和物理教育与科学素质培养．后来，又举办过两次会议，说明物理教学的改革在一步步地深化．笔者通过参加有关会议和亲身体验，对新情况下的物理教学有了新的理解．下面仅就我近来想到的、听到的，和被问到的问题，谈一些个人看法．     

Total internal reflection–refraction beam expander

Beam expanders being used presently have complex structure and none is perfect. A novel beam expander is proposed first. The beam expander can magnify (or decrease) the diameter of incident laser beam according to the theory of total internal reflection–refraction (TIR-R) principle. The characteristic of the beam expander was studied by using ray-tracing method and computer simulation. The beam expander can propagate a parallel laser beam along the propagation axis and would not change the propagation direction of the beam. For a nonparallel beam the Lagrange invariant (the product of diameter and divergence angle) is not constant. This beam expander would be an effective device in some applications.     

NⅡ离子2p4f—2p3d辐射跃迁概率的理论研究

在全相对论理论框架下，利用多组态Dirac-Fock(MCDF)方法，系统计算了NⅡ离子2p4f—2p3d的辐射跃迁概率，得到的结果与已有实验值符合很好.具体计算中，详细分析了相对论效应、电子关联、弛豫效应、Breit相互作用和量子电动力学(QED)效应对能级精细结构及辐射跃迁概率的影响.结果表明：相对论效应、电子关联和弛豫效应对NⅡ 2p4f-2p3d辐射跃迁概率有很重要的影响,考虑了这些效应后计算值得到明显改善.     

Compare study between smoothing efficiencies of epicyclic motion and orbital motion

The smoothing efficiencies of epicyclic motion and orbital motion in CCOS (computer controlled optical surfacing) were compared. CCOS polishing can smooth out mid-to-high spatial frequency errors which are smaller than tool size on optical mirrors due to the rigidity of polishing tools. The smoothing efficiencies of epicyclic motion and orbital motion with pitch lap and RC lap were compared and the result proved pitch lap with epicyclic motion smoothed ∼1.6 times faster than pitch lap with orbital motion while RC lap with epicyclic motion smoothed ∼1.85 times faster than RC lap with orbital motion.     

Pyridine-thermal synthesis and high catalytic activity of CeO2/CuO/CNT nanocomposites

Carbon nanotubes (CNTs) were controllably coated with the uninterrupted CuO and CeO₂ composite nanoparticles by a facile pyridine-thermal method and the high catalytic performance for CO oxidation was also found. The obtained nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction as well as X-ray photoelectron spectroscopy. It is found that the CuO/CeO₂ composite nanoparticles are distributed uniformly on the surface of CNTs and the shell of CeO₂/CuO/CNT nanocomposites is made of nanoparticles with a diameter of 30-60 nm. The possible formation mechanism is suggest as follows: the surface of CNTs is modified by the pyridine due to the π-π conjugate role so that the alkaline of pyridine attached on the CNT surface is more enhanced as compared to the one in the bulk solvent, and thus, these pyridines accept the proton from the water molecular preferentially, which result in the formation of the OH⁻ ions around the surface of CNTs. Subsequently, the metal ions such as Ce³⁺ and Cu²⁺ in situ react with the OH⁻ ions and the resultant nanoparticles deposit on the surface of CNTs, and finally the CeO₂/CuO/CNT nanocomposites are obtained. The T₅₀ depicting the catalytic activity for CO oxidation over CeO₂/CuO/CNT nanocomposites can reach ∼113 °C, which is much lower than that of CeO₂/CNT or CuO/CNT nanocomposites or CNTs.