一维Klein-Gordon双原子链中的能隙呼吸子

采用旋转波近似，讨论一维Klein-Gordon双原子链中的能隙呼吸子. 在驻波边界条件下数值求解一维Klein-Gordon双原子链晶格振动的运动方程组，得到不同耦合系数、不同非线性系数以及不同原子质量比情况下的以重原子为中心的对称模能隙呼吸子. 随着耦合系数的增大，原子之间的耦合作用增强，呼吸子的空间扩展范围增大；非线性作用越大，能隙呼吸子局域化越强；随着原子质量差的增大，呼吸子在空间越来越局域. 关键词： 能隙呼吸子 一维Klein-Gordon双原子链 耦合系数 非线性     

Discrete gap breathers in a two-dimensional diatomic face-centered square lattice

In this paper we study the existence and stability of two-dimensional discrete gap breathers in a two-dimensional diatomic face-centered square lattice consisting of alternating light and heavy atoms, with on-site potential and coupling potential. This study is focused on two-dimensional breathers with their frequency in the gap that separates the acoustic and optical bands of the phonon spectrum. We demonstrate the possibility of the existence of two-dimensional gap breathers by using a numerical method. Six types of two-dimensional gap breathers are obtained, i.e., symmetric, mirror-symmetric and asymmetric, whether the center of the breather is on a light or a heavy atom. The difference between one-dimensional discrete gap breathers and two-dimensional discrete gap breathers is also discussed. We use Aubry's theory to analyze the stability of discrete gap breathers in the two-dimensional diatomic face-centered square lattice.     

Periodic, quasiperiodic and chaotic discrete breathers in a parametrical driven two-dimensional discrete diatomic Klein--Gordon lattice

We study a two-dimensional (2D) diatomic lattice of anharmonic oscillators with only quartic nearest-neighbor interactions, in which discrete breathers (DBs) can be explicitly constructed by an exact separation of their time and space dependence. DBs can stably exist in the 2D discrete diatomic Klein--Gordon lattice with hard and soft on-site potentials. When a parametric driving term is introduced in the factor multiplying the harmonic part of the on-site potential of the system, we can obtain the stable quasiperiodic discrete breathers (QDBs) and chaotic discrete breathers (CDBs) by changing the amplitude of the driver. But the DBs and QDBs with symmetric and anti-symmetric profiles that are centered at a heavy atom are more stable than at a light atom, because the frequencies of the DBs and QDBs centered at a heavy atom are lower than those centered at a light atom.     

VO分子2Δ3/2-12Δ3/2电子跃迁P线系发射谱线的研究

本文利用孙卫国课题组建立的能精确计算(预言)某双原子分子电子态P线系发射谱线的物理新公式, 首次研究了VO分子从电子态²Δ_3/2跃迁到电子态1²Δ_3/2的(0, 0)跃迁带中的P线系发射谱线. 获得的研究结果不仅重复了实验上已知的低转动态谱线数据,而且还正确预言了该跃迁带在 实验上难以精确测量的转动量子数J=80.5以内的高振转激发态的P线系发射光谱. 为研究VO分子内部结构提供了重要的物理信息.     

Nonsequential double ionization of nonaligned diatomic molecules N2 and O2

Nonsequential double ionization (NSDI) processes of nonaligned diatomic molecules N2 and O2 are studied using the S-matrix theory. Our results show that the NSDI process significantly depends on the molecular symmetry and structure. The ratio of NSDI rate to single ionization rate as a function of the field intensity is obtained. It is found that N2 behaves closely with its companion atom Ar in the ratios over the entire intensity range, while O2 exhibits an obvious suppression effect, which is qualitatively consistent with the experiment.     

Line strength measurements of carbonyl sulfide (OCS) in the 2v3, v1+2v2+v3, and 4v2+v3 bands

To support planetary studies of the Venus atmosphere, we measured line strengths of the 2v₃, v₁+2v₂+v₃, and 4v₂+v₃ bands of the primary isotopologue of carbonyl sulfide (¹⁶O¹²C³²S), whose band centers are located at 4101.387, 3937.427, and 4141.212 cm⁻¹, respectively. For this, infrared absorption spectra in normal carbonyl sulfide (OCS) sample gas were recorded at an unapodized resolution of 0.0033 cm⁻¹ at ambient room temperatures using a Bruker Fourier transform spectrometer (FTS) at the Jet Propulsion Laboratory. The FTS instrumental line shape (ILS) function was investigated, which revealed no significant instrumental line broadening or distortions. Various custom-made short cells and a multi-pass White cell were employed to achieve optical densities sufficient to observe the strong 2v₃ and the weaker bands in the region. Gas sample impurities and the isotopic abundances were determined from mass spectrum analysis. Line strengths were retrieved spectrum by spectrum using a non-linear curve fitting algorithm adopting a standard Voigt line profile, from which Herman–Wallis factors were derived for the three bands. The band strengths of 2v₃, v₁+2v₂+v₃, and 4v₂+v₃ of ¹⁶O¹²C³²S (normalized at 100% of isotopologue) are observed to be 6.315(13)×10⁻¹⁹, 1.570(2)×10⁻²⁰, and 7.949(20)×10⁻²¹ cm⁻¹/molecule cm⁻², respectively, at 296 K. These results are compared with earlier measurements and the HITRAN 2004 database.     

The optimum regime of compression of Gaussian pulses in opposing interaction in a medium with cubic nonlinearity

In the present article the effect of compression of Gaussian pulses during their opposing propagation in a medium with inertial cubic nonlinearity is considered. Using methods of computer simulation, conditions are found that determine the optimum regime of compression. It is shown that after single passage through the medium the compression degree is equal to two. B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 840–842, November–December, 1997.     

Self-broadening, self-shift and self-mixing in the ν2, 2ν2 and ν4 bands of NH3

Using Fourier-transform spectra (Bruker IFS 120 HR, resolution ≈0.004 cm⁻¹) of NH₃ in nine branches of the ν₂, 2ν₂ and ν₄ bands, self-broadening and self-shift as well as self-mixing coefficients have been determined at room temperature (T=295 K) for more than 350 rovibrational lines located in the spectral range 1000–1800 cm⁻¹. A non-linear least-squares multispectrum fitting procedure, including line mixing effects, has been used to retrieve successively the line parameters from 11 experimental spectra recorded at different pressures of pure NH₃. The accuracies of self-broadening coefficients are estimated to be better than 2% for most lines. The mean accuracies of line-mixing and line-shift data are estimated to be about 15% and 25%, respectively. The results are compared with previous measurements and with values calculated using a semiclassical model based upon the Robert–Bonamy formalism that reproduces rather well the systematic experimental J and K quantum number dependencies of the self-broadening coefficients.The results concerning line mixing demonstrate a large amount of coupling between the symmetric and asymmetric components of inversion doublets mainly in the ν₄ band. The line mixing parameters are both positive and negative. More than two thirds of the lines studied here have a positive shift coefficient. However, for most of them the shift coefficients are negative in the 2ν₂ band. They are positive for the R branch of the ν₂ band and for the ^PR and ^RP branches of the ν₄ band. For the other branches they are both positive and negative. Some components of inversion doublets illustrate a correlation between line mixing and shift phenomena demonstrated by a quadratic pressure dependence of line position.     

GeS2-Ga2S3-CsCl玻璃的三阶非线性光学性能研究

用传统的熔融急冷法制备了组分为(100-2x) GeS₂-xGa₂S₃-xCsCl (x= 15, 20, 25 mol%)系列硫卤玻璃, 测试了样品玻璃的吸收光谱. 采用Z-扫描方法测试了样品的三阶非线性光学特性. 分析了激光光子能量与玻璃三阶非线性光学特性的关系,并研究了组分变化对玻璃的三阶非线性性能的影响. 研究结果表明,光子能量的少许改变可以使非线性吸收系数在一个较大的范围内变化,随着光子能量的增大, 玻璃的非线性吸收系数β 增大;当光子能量趋近于0.5E_g时, β值趋近于0,玻璃有最佳的品质因子; 玻璃样品中CsCl含量的增加使得玻璃的光学带隙E_g增大,短波截止边蓝移,非线性吸收系数β 减小. 但是由于结构与带隙对光学非线性的影响相反,非线性折射率γ 值变化不大. 该结果表明样品的光学非线性性能由光学带隙和结构两方面因素共同决定,对今后研究全光开关用硫系玻璃具有一定的指导意义和参考价值.     

Ferroelectricity in a diatomic Ising chain as investigated by the elastic Ising model

An elastic Ising model for a one-dimensional diatomic spin chain is proposed to explain the ferroelectricity induced by the collinear magnetic order with a low-excited energy state. A statistical theory based on this model is developed to calculate the electrical and magnetic properties of Ca₃CoMnO₆, a typical quasi-one-dimensional diatomic spin chain system. The calculated ferroelectric polarization and dielectric susceptibility show a good agreement with recently reported data on Ca₃Co_2-xMn_xO₆ (x ≈0.96) (Phys. Rev. Lett. 100 047601 (2008)), although the predicted magnetic susceptibility does not coincide well with experiment. We also address the rationality and deficiency of this model by including a first-order correction which improves the consistency between the model and experiment.     

NH3 self-broadening coefficients in the ν2 and ν4 bands and line intensities in the ν2 band

Self-broadening coefficients of NH₃ in the ν₂ and ν₄ bands and absolute line intensities in the ν₂ band have been measured at room temperature for some selected lines in the P- and R-branches. Using a Fourier transform spectrometer, line intensities and collisional widths were obtained by fitting Voigt profiles to the measured shapes of the lines. The results of self-broadening coefficients are in reasonable agreement with calculated linewidths using a semiclassical model which reproduce rather well the systematic experimental J and K quantum numbers dependencies. Satisfactory agreement was also obtained for line intensities with previous measurements in the ν₂ band. From the intensity measurements, we have determined effective transition dipole moments as well as Herman–Wallis parameters for the ν₂ band.     

Discrete breathers in a model with Morse potentials

Under harmonic approximation, this paper discusses the linear dispersion relation of the one-dimensional chain. The existence and evolution of discrete breathers in a general one-dimensional chain are analysed for two particular examples of soft (Morse) and hard (quartic) on-site potentials. The existence of discrete breathers in one-dimensional and two-dimensional Morse lattices is proved by using rotating wave approximation, local anharmonic approximation and a numerical method. The localization and amplitude of discrete breathers in the two-dimensional Morse lattice with on-site harmonic potentials correlate closely to the Morse parameter a and the on-site parameter к.     

中红外高双折射高非线性宽带正常色散As2 S3光子晶体光纤

设计了一种中红外As₂S₃光子晶体光纤,利用多极法研究了这种光纤的双折射、色散和非线性特性.数值研究发现,该光纤在中红外波段λ = 3.625 μm处双折射B高达0.098;其x偏振方向的非线性系数γ_x达到了1.69 m^-1 ·W^-1, y偏振方向的非线性系数γ_y达到了0.78 m^{- 关键词： 光子晶体光纤 中红外波段 双折射 非线性}     

Self-modulation of Bessel-Gaussian wave beams in a medium with cubic nonlinearity

A semi-discrete dynamic model has been developed for the formation of the spatial structure of wave fields in a medium with cubic nonlinearity. The characteristic features of self-focusing and conical modulation of intense Bessel-Gaussian light beams of different orders have been studied in different stages of their evolution during propagation. It has been shown that as a result of nonlinear refraction, in the far zone wave structures are formed consisting of three spatially separated conical beams. Increasing the cone angle of the wave vectors leads to a decrease in the effect of conical modulation of the radiation, and improves the structural stability of the beam. The considered self-modulation effects can be used for passive limiting of the laser radiation power. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 626–630, September–October, 2006.     

First-principles study on the electronic structure and optical properties of T12Cd2（SO4）3 and Rb2Cd2（SO4）3

With the help of ab initio full-potential linearized augmented plane wave （FPLAPW） method, calculating the electronic structure and linear optical properties is carried out for XCd2（SO4）3 （X =Tl, Rb）. The results show that Tl2Cd2（SO4）3 （TlCdS） has a larger band gap than Rb2Cd2（SO4）3 （RbCdS） and the energy bands for RbCdS are more dispersive than those of TlCdS. From their partial densities of states （PDOS）, we have observed that the hybridization between S ionic 2p and O atomic 2p orbitals forms SO4 ionic groups. The remarkable difference between RbCdS and TlCdS is, however, the degree of hybridization between cation （Tl and Rb） and its surrounding oxygen atoms. In the view of quantum chemistry, the strong p-d hybridization indicates the existence of their cation ionic bonds （Cd-O, Rb-O, and Tl-O）. The calculations of TlCdS and RbCdS show their optical properties to be less anisotropic. Their anisotropies in the optical properties mainly occur in a low photon energy region of 5-16 eV.     

钪原子的自电离里德伯能级3d4s(1D2)nf2 D3/2,3d4s(1D2)nf2 F5/2和3d4s(1D2)np2 D3/2<

在多通道量子亏损理论框架下,利用相对论多通道理论,分别在冻结实近似和考虑偶极极化下计算钪原子的J^π=(3/2)^-,(5/2)^-的三个收敛于 3d4s(¹D₂)的自电离里德伯系列的能级.对3d4s(¹D₂)np²D_3/2和3d4s(^{1 关键词： 相对论多通道理论 多通道量子亏损理论 电子-电子关联 自电离里德伯系列}     

一维双原子链中杂质引起的局域振动模

对含杂质的一维双原子链,在链中所有原子之间近邻相互作用力常数均相等的情况下,数值求解晶格振动的运动方程组,得到不同局域振动模的振动图像和产生条件,给出了局域模关于杂质原子质量和原胞中两种晶格原子质量比分布的相图．     

The third-order optical nonlinearity of The pyrochlore phase 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 thin film on quartz

The xPb(Mg_1/3Nb_2/3)O₃–(1−x)PbTiO₃ (PMNT) (with x=0.7) thin film is prepared on quartz substrates prepared using a sol–gel process. The PMNT thin film has a well-crystallized pyrochlore phase structure. The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility χ⁽³⁾ of the thin film have been determined by the Z-scan technique performed at 800 nm with a femtosecond laser. The nonlinear refraction index coefficient γ, the nonlinear absorption coefficient β of the thin film are 1.37×10⁻¹² cm²/W and −6.73×10⁻⁸ m/W, respectively. The real and imaginary part of the third-order nonlinear susceptibility of the film are 1.06×10⁻¹⁷ and −1.65×10⁻¹⁹ m²/V², respectively. The results suggested that the nonlinearity is dominated by the refractive for the film.     

Study on the structure dependent ultrafast third-order optical nonlinearity of GeS2–In2S3 chalcogenide glasses

The results of the femtosecond time-resolved optical Kerr at 820 nm in GeS₂–In₂S₃ chalcogenide glasses indicate that the response time in GeS₂–In₂S₃ glasses is subpicosecond, which is predominantly due to the distortion of the electron cloud. The value of χ⁽³⁾ in 0.95GeS₂–0.05In₂S₃ glass is also as large as 2.7 × 10⁻¹³ esu, and it reduces with the addition of In₂S₃, which may be ascribed to the microstructure evolution of GeS₂–In₂S₃ glasses. It is deduced that the intrinsic [Ge(In)S₄] tetrahedral structure units that possess the high hyperpolarizability may do great contribution to the enhancement of third-order optical nonlinearity while [S₃Ge–GeS₃] ethane-like molecular units make no considerable contribution to that in femtosecond time scale. These GeS₂–In₂S₃ and GeS₂–In₂S₃-based chalcogenide glasses would be expected to be the promising materials for all-optical switching devices.     

Magnetic structure of the cubic U2Te3 with a non-stoichiometric Th3P4 type of structure

The neutron diffraction patterns of the cubic U₂Te₃ have been obtained at 15 and 150 K. There are no extrapeaks of magnetic origin below the Curie point T_c = 70 ± 5 K. Thus the ordering corresponds to a collinear ferromagnetic structure. The value of the magnetic moment is 1.78 μ_B which is close to those values determined for a few cubic uranium pnictides and chalcogenides.