全国部分地区非物理类专业大学生物理竞赛题解 第十七届非物理类专业大学生物理竞赛试题及解答(续)

13.(10分 )　如图所示 ,一金质圆环以其边缘为支点直立在两磁极间 ,环的底部受两个固定档的限制 ,使其不能滑动 现环受一扰动偏离竖直面 0 .1弧度 ,并开始倒下 已知Ｂ =0 .5Ｔ ,环半径ｒ1=4ｃｍ ,环截面半径ｒ2 =1ｍｍ ,金的电导率为σ =4 .0× 10 7/Ω·ｍ ,设环重Ｆ =0 .0 75Ｎ ,并可以认为环倒下的过程中重力矩时时都与磁力矩平衡 ,求环倒下所需的时间ｔ 　　解 :依题意 ,在环倒下的过程中偏离原竖直方向θ角时 ,通过环面的磁通量为Φ =πｒ21Ｂｓｉｎθ (1)它变化引起的感应电动势为ε=ｄΦｄｔ =πｒ21Ｂｃｏｓθｄθｄｔ (2 )因为圆…     

Interaction of the Light Field with N Atoms Possessing Dipole-dipole Interaction

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｉｎｔｈｅｆｉｅｌｄｏｆａｔｏｍｏｐｔｉｃｓ,ｂｒｅａｋｔｈｒｏｕｇｈｓｉｎｔｈｅｅｖａｐｏｒａｔｉｖｅｃｏｏｌｉｎｇｏｆｄｉｌｕｔｅａｌｋａｌｉｇａｓｅｓｈａｖｅａｌｌｏｗｅｄｔｈｅｇｅｎｅｒａｔｉｏｎｏｆＢｏｓｅ Ｅｉｎｓｔｅｉｎｃｏｎｄｅｎｓａｔｅｓ(ＢＥＣ) [1,2 ] .Ｓｉｎｃｅｔｈｅｎ ,ｔｈｅｒｅｈａｖｅｂｅｅｎｍａｎｙｉｎｔｅｒｅｓｔｓｉｎｃｒｅａｔｉｎｇａｎａｔｏｍｌａｓｅｒａｎｄｅｘｐｌｏｒｉｎｇｉｔｓｎｏｖｅｌｐｒｏｐｅｒｔｉｅｓ[3 ] .Ｔｈｅｆｉｒｓｔａ…     

Self -frequency- doubling Laser from 1331.0 nm to 665.5 nm in Nd∶GdCOB Crystal

ＨｉｇｈｏｐｔｉｃａｌｑｕａｌｉｔｙＮｄ∶ＣｄＣＯＢｃｒｙｓｔａｌ (7%Ｎｄ,2 5× 40ｍｍ3)ｕｓｅｄｉｎｔｈｅｅｘｐｅｒｉｍｅｎｔｗａｓｇｒｏｗｎｗｉｔｈＣｚｍｅｔｈｏｄ.ＴｗｏｃｒｙｓｔａｌｓｐｅｃｉｍｅｎｓａｒｅｃｕｔａｔｔｙｐｅＩｐｈａｓｅｍａｔｃｈｉｎｇ:ｆｏｒｓｐｅｃｉｍｅｎ 1 ,θ=66.5°,=1 45.5°;ｆｏｒｓｐｅｃｉｍｅｎ 2 ,θ=65°,=3 4 .6°.Ｕｓｉｎｇｐｌａｎｅ (2 0 1 ) ,(4 0 1 )ａｎｄ (0 1 0 )ａｓｐｌａｎｅｏｆｒｅｆｅｒｅｎｃｅ,ｔｈｅｒｅｓｐｅｃｔｉｖｅａｎｇｌｅｓｏｆｓｐｅｃｉｍ…     

A Novel Single-beam Magneto-optical Atom Trap

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｓｉｎｃｅｔｈｅｍａｇｎｅｔｏｏｐｔｉｃａｌｔｒａｐ(ＭＯＴ)ｗａｓｆｉｒｓｔｐｒｏｐｏｓｅｄａｎｄｄｅｍｏｎｓｔｒａｔｅｄｂｙＲａａｂｅｔａｌ.[1],ｉｔｈａｓｂｅｃｏｍｅａｎｉｍｐｏｒｔａｎｔｔｅｃｈｎｉｑｕｅｆｏｒｐｒｅｐｒｅｐａｒｉｎｇａｃｏｌｄａｎｄｄｅｎｓｅａｔｏｍｉｃｓａｍｐｌｅａｎｄｈａｓｏｂｔａｉｎｅｄｗｉｄｅａｐｐｌｉｃａｔｉｏｎｓｉｎａｔｏｍｉｃｐｈｙｓｉｃｓ(ｉｎｃｌｕｄｉｎｇＢｏｓｅＥｉｎｓｔｅｉｎｃｏｎｄｅｎｓａｔｉｏｎｉｎａｔｏｍｉｃｇａｓ…     

平均原子辐射振子强度研究

本文以相对讨论Ｈａｆｔｒｅｅ－Ｆｏｃｋ－Ｓｌａｔｅｒ自洽场平均原子模型为基础，计算了金和铁元素电偶极辐射振子强度，研究了典型谱线振子强度随等离子体温度、密度的变化规律。     

类锂铝离子能级结构及光谱线性质的理论计算

用Ｈａｒｔｒｃｅ－Ｆｏｃｋ－Ｒｅｌａｔｉｖｉｓｔｉｃ（ＨＦＲ）自洽场方法,计算类锂铝离子１ｓ＾２ｎｌ（ｎ＝２～７,ｌ＝０～５）,１ｓｎｌｎ’ｌ’（ｎ,ｎ’＝２～３,ｌ,ｌ’＝０～２）各能级值,电偶极跃迁谱线的光谱线性质（波长、振子强度和跃迁几率）,其波长计算值和现有文献结果符合得较好。特别是实验中已观察到的软Ｘ射线激光跃迁（３ｄ－４ｆ,３ｄ－５ｆ）的波长值与我们的计算值符合得也很好。     

CuⅠ-AsⅤ离子3d104s-3d94s4p跃迁组态的能级和振子强度

利用组态相互作用理论和参数拟合内插的方法计算了类铜ＣｕⅠ－ＡｓⅤ离子３ｄ１０４ｓ－３ｄ９４ｓ４ｐ跃迁组态的能级、谱线波长和电偶极跃迁的振子强度。３ｄ９４ｓ４ｐ组态能级的所有计算结果与现有实验数据符合得很好。而ＺｎⅡ和ＧａⅢ离子的大部分能级纯属预测计算结果。给出了３ｄ１０４ｓ－３ｄ９４ｓ４ｐ能级跃迁的谱线波长和振子强度。     

BOPUXUE ZAZHI(CHINESE JOURNAL OF MAGNETIC RESONANCE)GENERAL CONTENTS

Ｖｏｌ.18　Ｎｏ .1　Ｍａｒ.2 0 0 1ＳｔｕｄｙｏｆｔｈｅＲｅａｃｔｉｏｎｏｆＰｄ(ＯＡｃ) 2 ｗｉｔｈＰＰｈ3ｉｎＣＣｌ4　　　　　………………………ＷＥＩＦｅｎｇ ｐｉｎｇ ,ＨＵＡＮＧＹｏｎｇ ｒｅｎａｎｄＦＥＮＧＬｉａｎｇ ｂｏｅｔａｌ.　 ( 1 -5)…………ＰａｒａｍａｇｎｅｔｉｃｇＦａｃｔｏｒｏｆＺｎＳ :Ｃｏ2 +Ｃｒｙｓｔａｌ 　　　　　……………………………………ＸｉｅＬｉｎ ｈｕａ ,ＨｕＰｉｎｇａｎｄＺｈａｏＭｉｎ ｇｕａｎｇ　 ( 7-1 1 )……………………………ＡＳｔｕｄｙｏｆｔｈｅＣｈａｉｎＭｏｔｉｏ…     

Annual Cumulative Contents of Volume B11.Chinese Journal of Lasers(2002)

·ＬＡＳＥＲＤＥＶＩＣＥＳ·ＥｘｐｅｒｉｍｅｎｔａｌＳｔｕｄｙｏｎＡｃｔｉｖｅ ｐａｓｓｉｖｅＭｏｄｅ ｌｏｃｋｉｎｇＵｓｉｎｇＣｒ4 + ∶ＹＡＧａｓＳａｔｕｒａｂｌｅＡｂｓｏｒｂｅｒ1 61 1ＡＭｉｃｒｏｃｈｉｐＴｕｎａｂｌｅＢｌｕｅＬａｓｅｒＳｏｕｒｃｅＢａｓｅｄＵｐｏｎＣｒ∶ＬｉＳＡＦｉｎＣｏｎｔａｃｔｗｉｔｈＫＮＣｒｙｓｔａｌ1 61 5ＨｉｇｈＰｏｗｅｒ 940ｎｍＡｌ ｆｒｅｅＡｃｔｉｖｅＲｅｇｉｏｎＬａｓｅｒＤｉｏｄｅｓａｎｄＢａｒｓｗｉｔｈａＢｒｏａｄＷａｖｅｇｕｉｄｅ1 61 91 .3 2 μｍＮｄ3+ ∶Ｙ…     

类镍离子（HfXL Ⅴ—ReXLⅧ）能级和振子强度的理论计算

利用多组态Ｈａｒｔｒｅｅ—Ｆｏｃｋ—Ｒｅｌａｔｉｖｉｓｔｉｃ（ＨＦＲ）理论系统地从头计算了类镍离子（ＨｏＬⅤ－ＲｅＸＬⅧ）的能级、电偶极跃迁波长和振子强度。计算结果与实验符合得较好，为我们的高Ｚ元素激光等离子体光谱实验分析提供了重要依据。     

Photodetachment dynamics of H~- ion in a harmonic potential plus a time-dependent oscillating electric field

The photodetachment dynamics of H~- ion in a harmonic potential plus an oscillating electric field is studied using the time-dependent closed orbit theory. An analytical formula for calculating the photodetachment cross section of this system is put forward. It is found that the photodetachment cross section of this system is nearly unaffected for the weak oscillating electric field strength, but oscillates complicatedly when the oscillating electric field strength turns strong. In addition, the frequency of the harmonic potential and the oscillating electric field(the frequency of the harmonic potential and the frequency of the oscillating electric field are the same in the paper, unless otherwise stated.) can also affect the photodetachment dynamics of this system. With the increase of the frequency in the harmonic potential and the oscillating electric field, the number of the closed orbits for the detached electrons increased, which makes the oscillatory structure in the photodetachment cross section much more complex. Our study presents an intuitive understanding of the photodetachment dynamics driven by a harmonic potential plus an oscillating electric field from a space and time dependent viewpoint.This study is very useful in guiding the future experimental research for the photodetachment dynamics in the electric field both changing with space and time.     

Neutron Scattering and Vibrational Spectra of Molecular Crystals

Infrared and Raman spectra of a number of molecular crystals have been measured for studying molecular vibrations and the intermolecular and intramolecular force fields. The infrared absorption bands arise from interaction of the electric wave with the oscillating dipole moment of the crystal. Raman scattering covers inelastic photon scattering processes and accordingly Raman lines arise from the oscillating polarizability of the crystal. Thus, the vibrational modes observed in infrared absorption or Raman scattering spectra are k = 0 modes, for which translationally equivalent molecules vibrate in phase.     

A multi-energy-level lattice Boltzmann model for Maxwell’s equations without sources

A lattice Boltzmann model for the Maxwell’s equations without sources is proposed by taking separate sets of distribution functions for the electric and magnetic fields and using the higher-order moment method. The higher-order moment method is based on the solution of a series of partial differential equations obtained by multi-energy-level techniques, multi-scale techniques, and Chapman–Enskog expansion, As numerical examples, some classical electromagnetic phenomena, such as the electric field and equipotential lines around an electrostatic dipole, the electric and magnetic fields around oscillating dipoles are given. These numerical results agree well with classical ones.     

Transmission of electric dipole radiation through an interface

We consider the transmission of electric dipole radiation through an interface between two dielectrics, for the case of a vertical dipole. Energy flows along the field lines of the Poynting vector, and in the optical near field these field lines are curves (as opposed to optical rays). When the radiation passes through the interface into a thicker medium, the field lines bend to the normal (as rays do), but the transmission angle is not related to the angle of incidence. The redirection of the radiation at the interface is determined by the angle dependence of the transmission coefficient. This near-field redistribution is responsible for the far-field angular power pattern. When the transmission medium is thinner than the embedding medium of the dipole, some energy flows back and forth through the interface in an oscillating fashion. In each area where field lines dip below the interface, an optical vortex appears just above the interface. The centers of these vortices are concentric singular circles around the dipole axis.     

Temporal interference driven by an oscillating electric field in photodetachment of H~- ion

The real time domain interferometry for the photodetachment dynamics driven by the oscillating electric field has been studied for the first time. Both the geometry of the detached electron trajectories and the electron probability density are shown to be different from those in the photodetachment dynamics in a static electric field. The influence of the oscillating electric field on the detached electron leads to a surprisingly intricate shape of the electron waves, and multiple interfering trajectories generate complex interference patterns in the electron probability density. Using the semiclassical open-orbit theory, we calculate the interference patterns in the time-dependent electron probability density for different electric field strengths, different frequencies and phases in the oscillating electric field. This method is universal, and can be extended to study the photoionization dynamics of the atoms in the time-dependent electric field. Our study can guide the future experimental researches in the photodetachment or photoionization microscopy of negative ions and atoms in the oscillating electric field.     

复合场下优化产生粒子对能量分布宽度的特性研究

采用计算量子场论的方法,对振荡场加稳恒场的组合外场下真空中正反粒子对的产生特性进行了研究.通过一系列的对比得到当振荡场的宽度减小时,一方面可增加正反粒子对的产生量,另一方面也可减小正反粒子对的能量分布宽度从而得到能量单一性更好的粒子对.同时,通过分析产生量、能量分布宽度与振荡场宽度的关系可得出,仅在一定范围内减小振荡场的宽度可使能量分布更加集中,则能量分布宽度趋于某个极限值.因此,要得到产生量多且能量分布集中的正反粒子对应选择合适的参数,这可为今后的实验设计提供数据参考.     

强场下真空中粒子对产生的研究进展

随着激光技术的飞快发展,激光强度不断提高,超强外场下真空中正负电子对产生的过程,即能量向质量转化过程,已经成为一个研究热点。主要综述了近几年量子Vlasov方程方法和计算量子场论(数值求解Dirac方程)方法在研究强场下真空中正负电子对产生方面的进展,分别介绍了空间均匀场和空间不均匀场下的粒子对产生的情况。第一种情况主要介绍双脉冲结构振荡电场中电子-正电子对的产生、强双频振荡电场中非微扰电子-正电子对的产生、频率调制的激光场中电子-正电子对的产生和Dirac真空对啁啾外场的快速分辨。第二种情况主要介绍优化空间局域电场提高粒子对的产生率、多个势阱-垒结构的振荡场对粒子对产生的增强、振荡 Sauter 电势中正负电子对产生的问题、操纵Dirac真空以控制其在场诱导下的衰变、作为信息传输介质的Dirac真空还有正负电子对产生中的相干和非相干啁啾机制的转变。     

Li里得堡原子在振荡场中的回归谱研究

文中应用扩展的半经典闭合轨道理论计算了Li原子在平行电磁场加一个振荡电场中的回归谱.与相同情况下平行电磁场中的回归谱比较,当附加含时振荡场时,静外场中的吸收光谱的强度被很大程度地减弱.另外,分别讨论了回归谱强度随振荡场振幅以及频率的变化规律.     

电磁波与电离波面相互作用过程中的静磁场模和振荡电场

利用了匀速运动的均匀等离子体中电磁场的色散关系，对电磁波与由强激光驱动的运动电离波面的相互作用过程中出现的静磁模进行了研究，发现在特定的条件下振荡电场也会在该过程中出现，并确定了振荡电场产生的条件 关键词：     

双模纠缠相干光场与V型三能级原子相互作用系统的原子偶极压缩效应

采用求解Schroedinger方程和数值计算方法，研究了双模纠缠相干光场与V型三能级原子相互作用过程中原子偶极算符的压缩效应，结果表明：此压缩效应与双模纠缠光场的纠缠程度、失谐量相关联。