Noether-Form Invariance of Nonholonomic Controllable Mechanical Systems in Phase Space

In this paper, we study the Noether-form invariance of nonholonomic mechanical controllable systems in phase space. Equations of motion of the controllable mechanical systems in phase space are presented. The definition and the criterion for this system are presented. A new conserved quantity and the Noether conserved quantity deduced from the Noether-form invariance are obtained. An example is given to illustrate the application of the results.     

高斯光束在外加空间调制电场的光折变晶体中的演化

研究了高斯光束在外加空间调制电场的光折变晶体中的演化,结果表明,在不同的外加调制电场作用下高斯光束的光场分布会随着外电场变化而被调制。重点研究了同相位和反相位以及相位差为π/2的高斯光束在外加空间调制电场的光折变晶体中的相互作用,在外加空间分布线性增加电场作用下出现了许多新的实用特性,通过调整外加电场分布,可以让两同相位相干光靠得更近而不发生融合,也可以让两靠得很近的反相位光束可控偏转,还可以控制相位差为π/2的两相干光束进行能量转移。这种连续变化的电场可以用阶梯分布的电场替代,为工程实现提供了可能。     

低能离子束横向发射度的测量及分析

The transverse emittance of an ion beam describes its transverse size as the particles are transported from a source to a target.It allows for predicting beam losses in limiting apertures and the beam focus size at the target.Various definitions and issues are discussed.The most common and emerging measuring techniques are presented,including their advantages.Several methods of emittance data analysis,their accuracy and trustworthiness,are discussed.     

可控硅外特性的研究

开发和推广可控硅特性研究的物理实验,意在启发学生对物理实验的趣味性和思考方法,让学生在实验课中根据观察到的现象和实验数据在实验课后进行分析,最后判断并得出结论.     

Creation evidence of the second non-dispersive Zakharenko wave by helium atomic beams in superfluid helium-II at low temperatures

In this work, the experimental results of the creation of the second non-dispersive Zakharenko wave (C _ph = C _g ≠ 0) in the negative roton branch (the so-called second sound) of the bulk elementary excitations (BEEs) energy spectra are introduced. Several BEE signals detected by a bolometer situated in the isotopically pure liquid helium-II at low temperatures ∼100 mK are shown, which give evidence of negative roton creation in the liquid by helium atomic beams striking the liquid surface. The negative roton signals were clearly distinguished by the following ways: the negative roton signal created by helium atomic beams appeared earlier than the positive roton signal created by the beams, and presence of both positive and negative roton signals together. It is natural that the negative roton creation by the beams requires the ⁴He-atom energies ∼12 K, while the positive roton creation by the atomic beams requires energies ∼35 K. Therefore, successive increase in the heater power resulting in an increase in the ⁴He-atom energies gives solid evidence that the negative rotons are first created in the liquid by the helium atomic beams.      

天鹅绒阴极产生的双脉冲强流相对论电子束特性实验研究

在时间分辨的模式下, 实验研究了天鹅绒阴极产生的双脉冲相对论强流电子束的束心运动、束包络和束的发射度. 在实验中, 电子束流强度和电子束心运动用电阻环进行测试, 而电子束和石英玻璃的相互作用产生的契仑科夫辐射用来给出电子束包络和发射度信息. 电子束和石英玻璃作用产生的契仑科夫辐射用1台8幅分幅相机记录. 实验结果表明, 天鹅绒阴极产生的相对论强流双脉冲电子束在束流大小、束心运动轨迹、束包络及束发射度等方面具有较好的一致性.     

Flat-topped Mathieu-Gauss beam and its transformation by paraxial optical systems

In order to avoid the severe axial intensity oscillations which appear when an ideal Mathieu beam is truncated, we propose to modulate it by a flattened multi-Gaussian envelope. The obtained beam, which is referred as flattened Mathieu-Gauss (FTMG) beam, can be expanded into a finite series of Mathieu-Gauss beams with various waists. The propagation study of this beam reveals that the axial intensity is unchanged within a certain propagation distance as for super-Gaussian-Bessel beams or Gori’s flattened Bessel beams. By using Collins formula, we derive closed-form expressions of FTMG beam propagating through a paraxial axisymmetric ABCD optical system. Some numerical calculations and discussions are also given.     

Studies of propagation characteristics of elliptical Gaussian beams through circular apertured optical systems

An approximate analytical propagation formula of the elliptical Gaussian beams through a paraxial ABCD optical system with a circular aperture is obtained on the basis of the expansion of a hard-edged aperture into a finite sum of complex Gaussian functions. And the parameter characteristics of the truncated beams including the beam propagation factor and the kurtosis parameter are also studied in detail by using the second-order-moments method.     

无衍射光的干涉实验与理论分析

分析了两束无衍射光的干涉场分布形式和干涉条纹轨迹。将一束单色光入射两小孔产生的两束相干光照射轴锥镜,在轴锥镜后将产生两束无衍射光。根据单束倾斜光入射轴锥镜的无衍射理论,分析出这两束无衍射光产生的干涉场为每束无衍射光的无衍射场的线性叠加。利用零阶贝塞尔函数的零点公式,推导出两束无衍射光的干涉条纹的轨迹为双曲线。计算结果表明,干涉场中两中心的间距与两孔实际的间距和干涉场距轴锥镜的距离成正比。实验结果与理论仿真相一致。     

Propagation properties of a partially polarized electromagnetic twist anisotropic Gaussian Schell-model beam in turbulent atmosphere

Based on the extended Huygens-Fresnel integral formula, analytical formulae for the elements of cross-spectral density matrix of partially polarized electromagnetic twist anisotropic Gaussian Schell-model (TAGSM) beam propagating in turbulent atmosphere can been derived by a tensor method. Our main attention was focus on the effect of the atmospheric turbulence, twist parameters and partial coherence on the spectral degree of polarization, the spectral degree of coherence and the spectral density. Numerical calculation results and analysis are given.