Vol. 55, No. 9 (2006)
2006-05-05
GENERAL
2006, 55 (9): 4397-4406.
doi: 10.7498/aps.55.4397
Abstract +
The linear transient eddy current electromagnetic field problem for determining solution is characterized by replacing the interface condition of the tangential component of the electric field intensity by the interface condition of the normal component of the magnetic flux density, and ignoring the displacement current in the constraint equations. In is a fundamental theoretical problem whether the solution to the irregular problem for determining solution in unique and stable. In this paper, we introduce a scalar potential function in the nonconducting region,and prove the existence of an auxiliary function which is important to the problem. After deriving the energy estimate inequality, the uniqueness and stability of the solution to the linear transient eddy current electromagnetic field problem for determining solution are proved. The results of the paper can provide theoretical basis for analyzing and calculating the linear transient eddy current electromagnetic field problem. As an application example, we present the analytical solution to the eddy current problem that a single-turn coil driven by solitary pulse current is arranged coaxially with a spherical conductor.
2006, 55 (9): 4407-4413.
doi: 10.7498/aps.55.4407
Abstract +
This paper has derived a new molecular model for simulating semi-rigid main-chain LCPs (liquid crystalline polymers) based on the traditional GB (Gay-Berne)/LJ (Lennard-Jones) model, named Solo-LJ-SP-GB model. A single LJ unit and two nonlinear springs have been firstly used to describe the flexible spacers between GB units in the LCPs. Using the current model, the simulation time is less than 10% of that spent by using the traditional GB/LJ model, when simulating the semi-flexible main-chain LCP of 169 molecular chains with 6 flexible spacers between neighboring GB units, which greatly enhances the computational efficiency. Through using the current model to study the phase behaviors of semi-flexible main-chain LCPs, the odd-even effects of thermodynamic properties depending on the number of flexible spacers and the phase transition from isotropic to liquid crystalline have been observed, which agrees well with the existing experimental data and the simulation results of the traditional model. It is shown that the new model enables to describe the structural properties of semi-rigid main-chain LCPs accurately.
2006, 55 (9): 4414-4419.
doi: 10.7498/aps.55.4414
Abstract +
New exact solutions in terms of the Jacobi elliptic functions are obtained for the nonlinear Schrdinger (NLS) equation by means of modified mapping method.
2006, 55 (9): 4420-4427.
doi: 10.7498/aps.55.4420
Abstract +
The turbulence synchronization is achieved in the excitable media via the mutual coupling method, the coupling coefficient is given and the largest transverse Lyapunov exponent is calculated. Turbulence is suppressed in two ways by coupling with two systems in different states.
2006, 55 (9): 4428-4432.
doi: 10.7498/aps.55.4428
Abstract +
Parikh recently viewed the black hole radiation as a semi-classical tunneling process, and showed that the radiation spectrum for the static Schwarzschild and Reissner-Nordstrm black holes is not pure thermal after considering the self-gravity interaction. In this paper, we adopt the new form of the Kerr solution presented by Doran and extend Parikh's work to investigate the tunneling radiation of a rotating black hole. We obtain a corrected radiation spectrum, which is related to the change of Bekenstein-Hawking entropy. It is not pure thermal, but is consistent with the underlying unitary theory.
2006, 55 (9): 4433-4436.
doi: 10.7498/aps.55.4433
Abstract +
Using the mass M, charge Q, angular momentum J and their corresponding πM,πQ,πJ of Kerr-Newman black hole, we obtain a six-dimensional space. We first establish the resonance model of black hole through criterion transforms. Then we make use of this model to analyze the quantum area spectrum of Kerr-Newman black hole.
2006, 55 (9): 4437-4441.
doi: 10.7498/aps.55.4437
Abstract +
The bifurcation control of period-doubling bifurcation in logistic model have been studied in this paper. The bifurcation maps of logistic model are achieved and the bifurcation characteristic of the dynamical system is changed by using variable-parameter linear controllers. In order to change the parameter value of all existing bifurcation points and modify the shape of a bifurcation chain, we can design variable controllers in for practical aims. Moreover, the bifurcation map may be obtained more effectively by adequately choosing the controller gain.
2006, 55 (9): 4442-4449.
doi: 10.7498/aps.55.4442
Abstract +
This paper presents a novel keyed one-way Hash function based on a chaotic dynamic S-Box together with traditional one-way Hash function construction. The proposed approach can give a chaotic Hash value by means of the look up table of functions and chaotic dynamic S-Box. Compared with the existing chaotic Hash functions, this method improves computational performance of Hash system by using the chaotic dynamical S-Box substitution in place of iterating the original message directly in chaos system. Theoretical and experimental results show that the proposed method has strong one way property, large key space, sensitivity to initial conditions and chaotic system's parameters.
2006, 55 (9): 4450-4454.
doi: 10.7498/aps.55.4450
Abstract +
This brief paper designs a novel chaotic system via convex-combining a unified system with Rssler system. The combined system includes a Unified-Rssler system with double parameters, a Lorenz-Rssler system and a Chen-Rssler system with single parameter. The chaotic intervals in Chen-Rssler system are determined by calculating maximum Lyapunov exponent spectrum and numerical simulation.
2006, 55 (9): 4455-4459.
doi: 10.7498/aps.55.4455
Abstract +
We present a method of anti-control of chaos on the degenerate optical parametric oscillator via modulating the reduced decay rate of the fundamental mode with a sinusoid wave to convert the steady state without output of subharmonical mode or periodic state into chaotic state. Numerical simulation shows that there are different chaotic orbits corresponding to different modulation amplitude and modulating angular frequency only if the maximum Lyapunov exponent of the system is positive. The maximum Lyapunov exponent as a function of modulation amplitude and modulating angular frequency is calculated respectively. We point out here that converting the steady state without output of subharmonical mode into chaotic state is more difficult than converting the periodic state into chaotic state because narrower range of modulation amplitude and modulating angular frequency can be used in the former case.
2006, 55 (9): 4460-4465.
doi: 10.7498/aps.55.4460
Abstract +
The growth of clusters on an inhomogeneous substrate is simulated by using Monte Carlo method. The inhomogeneous substrate is composed of two different kinds of regularly distributed materials A and B with different physical properties. Deposited particles have initial energy E0. It consumes energies EA and EB when a particle diffuses one step on phases A and B, respectively, and it consumes energy EAB when the particle passes through the phase boundary from A to B. In the simulation, E0 is much bigger than EA and EB, and the energy needed for the particle to pass through the phase boundary from B to A is set as EBA=0. Results show that the clusters aggregated on the inhomogeneous substrate are of fractal structure. When EAB is much bigger than EA and EB, the number, radius of gyration and fractal dimension of the cluster all vary periodically with ratio E0/EBA.
2006, 55 (9): 4466-4471.
doi: 10.7498/aps.55.4466
Abstract +
Primary particles produced in the early fire period evolve into bigger aggregates due to Brown coagulation, which take on fractal properties. In this article, smoke particle images were obtained by a field emission scanning electron microscope (SEM), and the fractal characteristics of the particles were analyzed based on the power law of fractal theory. By using digital image processing technique, more fractal parameters such as the fractal dimension, fractal prefactor, primary particles' size and radius of gyration were obtained. The results can provide a fundamental basis for fire smoke detection research.
2006, 55 (9): 4472-4477.
doi: 10.7498/aps.55.4472
Abstract +
Photodynamics of two kinds of peripheral antenna complexes light harvesting 2 (LH2) of Rb. Sphaeroides 601, namely the native LH2 and B800-released LH2, where B800-BChls were partially or completely removed with different pH treatments, were studied using femtosecond pump-probe technique at different laser wavelengths. The obtained results for these samples demonstrate that under the excitation around B800 absorption band, the photoabsorption and photobleaching dynamics are caused by the direct excitation of upper excitonic levels of B850 and excited state of B800 pigments, respectively.
2006, 55 (9): 4478-4482.
doi: 10.7498/aps.55.4478
Abstract +
Balsaming lens will be damaged when irradiated by laser of certain power. The model of one-dimension unstable temperature field during the interaction between multiple-pulse laser and material is established, and the transient temperature distribution of glass material of balsaming lens is calculated. The fusion moment and the moment when cementing material melts are researched by means of numerical calculation. Experiments about damage in several balsaming lenses of the same kind irradiated by multiple-pulse CO2 laser, the parameters of which are 10Hz, 200ns and 20WM, are carried out. It is found that when the irradiation time reaches 12s, the front surface of balsaming lens is molten. When the irradiation time reaches 30s, colorized dapples are suddenly formed in the cementing layer of samples. It indicates that cementing material is intenerated and balsaming lens is thoroughly damaged. The result of theoretical analysis exhibits good agreement with the experimental result.
ATOMIC AND MOLECULAR PHYSICS
2006, 55 (9): 4483-4489.
doi: 10.7498/aps.55.4483
Abstract +
Using one-color two-photon (1C2P) scheme, high-resolution mass analyzed threshold ionization MATI spectra of ethyl bromide have been recorded. Accurate values for the adiabatic ionization energy have been determined to be 83097±3 cm-1 and 85452±3 cm-1 for the X1 2E1/2 and X2 2E1/2 states of the cation， respectively, giving a splitting of 2355±6 cm-1. The ionic vibrational frequencies were also obtained, and the values were in agreement with high accuracy with the literature data. The spectra showed extensive excited vibrational structure as a result of wave packet evolving on the potential energy surface of the dissociative state in the time interval between the absorption of the two photons. The vibrational calibration was done based on the known vibrational frequencies of the neutral ethyl bromide. The spectrum was found to exhibit mainly vibrational modes involving the dissociation of the molecule, including some non-totally symmetric modes.
2006, 55 (9): 4490-4495.
doi: 10.7498/aps.55.4490
Abstract +
Quadratic configuration interaction (QCISD) method has been used to optimize the possible ground-state structures of BH2 and AlH2 molecules. The results show that the ground state of BH2 molecule has C2v symmetry and is in the 2A1 state. The parameters of structure and the harmonic frequencies are RBH=0.1187nm, ∠HBH=128.7914°, De=3.65eV,ν1(a1)=1020.103cm-1,ν2(a1)=2598.144cm-1 and ν3(b2)=2759.304cm-1, respectively. The results also show that the ground state of AlH2 molecule has C2v symmetry and is in the 2A1 state. The parameters of structure and the harmonic frequencies are of RAlH=0.1592nm, ∠HAlH=118.095°, De=2.27eV,ν1(a1)=780.81cm-1,ν2(a1)=1880.81cm-1 and ν3(b2)=1910.46cm-1, respectively. The potential energy functions of BH2 and AlH2 have been derived from the many-body expansion theory. The potential energy functions describe correctly the configurations and the dissociation energies of the two ground-state molecules. Molecular reaction kinetics of BH+H and AlH+H based on the potential energy functions is discussed briefly.
2006, 55 (9): 4496-4500.
doi: 10.7498/aps.55.4496
Abstract +
The low-lying excited states of the SiN cluster are studied using the time-dependent (TD) density functional theory (DFT). The calculated results compared well with the available theoretical ones and are used to assign the features of this cluster in photoelectron spectrum. The results indicate that the ground state of negative SiN is 1Σ, and the X and the A signals in photoelectron spectroscopy correspond to 1Σ→2Σ and 1Σ→2Π, respectively. It shows that TDDFT, by and large, can be used to get good results for the excited states of the SiN cluster.
2006, 55 (9): 4501-4505.
doi: 10.7498/aps.55.4501
Abstract +
The spectra shifts for the intercombination line (1s2p(3P1)→1s2) and the resonance line (1s2p(1P1) →1s2) of He-like neon, which are the two electronic dipole transitions in the Ｋα group emissions, are studied under dense plasma conditions by using the self-consistent field ion sphere model. The results show the two electronic dipole transitions red shift nearly linealy with the increase of plasma electron density. Moreover, the red-shift energy becomes more sensitive to the plasma electron density when the plasma electron temperature is lower. It is worthy to note that the energy discrepancy between these two spectral lines is equal to the exchange energy of state 1s2p(3P1). So, it is the first time that the exchange energy varying with plasma environment is observed both qualitatively and quantitatively. This result may be useful to dense plasma diagnosis in connection with variation of the relative position and the spectral fine structure splitting in high density plasmas.
2006, 55 (9): 4506-4513.
doi: 10.7498/aps.55.4506
Abstract +
Under the optimum experimental condition, the analytical spectral lines of the Fe and Ni trace elements in Pb-Cu alloy are determined in the experiment. The laser-induced breakdown spectroscopy(LIBS) calibration curves of the Fe and Ni trace elements are also determined in buffer gases He, Ar, Air and in vacuum. The standard fit errors for the calibration curves are in the range from 0.02 to 0.08.
2006, 55 (9): 4514-4519.
doi: 10.7498/aps.55.4514
Abstract +
A 2-D isotropic left-handed metamaterial (LHM) in C band with broad bandwidth and low loss is designed. The size of its unit cell is much smaller and configuration of its unit cell is symmetrical compared with previous LHM. The double negative (DNG) feature and the negative index of refraction (NIR) feature are verified by numerical simulation to prove the existence of the LHM. The numerical results show that the DNG and NIR phenomenon appear simultaneously as predicted.
2006, 55 (9): 4520-4527.
doi: 10.7498/aps.55.4520
Abstract +
Spectra of the ionized oxygen atom were researched with the Pro-500i monochromator equipped with CCD. The beam foil method was used at energy of 2 MeV in a 2×1.7 Tandem accelerator. In this work, we report 201 spectral lines determined in the region 250—350 nm, and most spectral lines were attributed to n，l energy level transitions from OⅡ to OⅣ atoms. Our experimental results are in good agreement with existing theoretical calculations. Many lines reported in this paper have not been measured in past experiments, and a majority of them are week transitional lines.
2006, 55 (9): 4528-4534.
doi: 10.7498/aps.55.4528
Abstract +
The laser-focused atomic deposition is a new way to build the nano transfer standard of high reliability adequate for application. Based on the semi-classical model, this paper starts from the motion equation of chromium atom in the laser standing wave field to get the trajectory of the atoms in the standing wave field by analytical simulation. The effects on focal line features are discussed as a result of the angular collimation, velocity spread in the atomic beam and the spherical aberration. The effects from different deposition positions are also discussed. This paper also gives a sample of the grating structure nanofabricated by laser focusing of Cr atoms.
2006, 55 (9): 4535-4541.
doi: 10.7498/aps.55.4535
Abstract +
Based on the theory of coupled-wave, the dispersion equation and coupling condition of helically corrugated waveguide are obtained by the method of impedance perturbation. Then the nonlinear coupled equations are obtained from the relativistic equation which describes the motion of electrons. The numerical calculation and analysis of cold cavity by PIC software are applied to analyze both hot and cold dispersion characteristics of this waveguide.
2006, 55 (9): 4542-4547.
doi: 10.7498/aps.55.4542
Abstract +
A systematic study on the equilibrium geometries and electronic properties of Y-doped gold clusters has been studied by density functional theory calculations. The stability and electronic properties of doped gold clusters are similar to that of pure gold clusters. Their inonization potential and electron affinities alter with odd-even oscillation as a function of the number of atoms. The magic-number behaviour is observed in the Y-doped gold cluster cations, which is in good agreement with the mass spectrum experiment. Thus Au2Y+ and Au6Y+ are more stable than other clustered cations. The most stable isomers of the Y-doped gold cluster tend to have the maximized coordination number of Au atom.
2006, 55 (9): 4548-4552.
doi: 10.7498/aps.55.4548
Abstract +
The geometric configuration and electronic structure of NaBen (n=1—12) clusters have been studied by using density functional theory (DFT).The results show that the atomic structures of NaBen (n=1—12) clusters are significantly different from the host geometries; the nearest inter-atomic distances of Na-Be and the energy gaps (HOMO-LUMO) oscillate with increasing size. It is found that at size n=4, 6 and 9, the clusters are more stable than neighboring ones, especially the NaBe4 cluster. Also, the evolution with increasing size for the electronic properties of NaBen (n=1—12) clusters are discussed.
2006, 55 (9): 4553-4556.
doi: 10.7498/aps.55.4553
Abstract +
Atomic structures of titanium trimer have been obtained at different spin multiplicities by means of density functional theory (DFT) method. Also, vibrational frequencies of corresponding atomic structures were calculated. The results indicate that effects of spin multiplicity on atomic structure of titanium trimer are remarkable, especially for bond distances and vibrational frequencies. After taking account of spin multiplicities, the ground state of titanium trimer is a septet.
CLASSICAL AREA OF PHENOMENOLOGY
2006, 55 (9): 4557-4562.
doi: 10.7498/aps.55.4557
Abstract +
Based on the generalized Lorenz-Mie theory (GLMT), the incident fundamental Gaussian beam is expanded in terms of the vector spherical harmonics. We present an expression of radiation trapping forces acting on a multilayered spherical particle in a Gaussian beam by using the theory of electromagnetic momentum, and, as an example, numerical results are given to an axial two-layer absorbing spherical particle, along with a discussion about the influence of the beam waist radius, relative complex refractive index and thickness of the two layers on trapping forces.
2006, 55 (9): 4563-4568.
doi: 10.7498/aps.55.4563
Abstract +
Based on the nonparaxial vectorial moment theory of light beam propagation proposed by Porras, the characteristic parameters, such as the beam width, far-field divergence angle and M2 factor of nonparaxial vectorial Laguerre-Gaussian (LG) beams with initial circular polarization, are derived and expressed in terms of a series sum. The nonparaxial vectorial Gaussian beam is treated as a special case of our result. It is shown that the second-order-moment based beam width propagates according to the hyperbolic law, and for w0/λ→0 (w0-waist width,λ-wavelength) the far-field divergence angle θ approaches 90°, which is larger than 63.435° predicated by the nonparaxial scalar theory. The M2 factor of nonparaxial vectorial LG beams depends not only on the mode index p, but also on the w0/λ. Finally, comparison between the propagation of nonparaxial vectorial LG beams and that of nonparaxial scalar LG beams indicates that the far-field divergence angle is greatly influenced by the vectorial effect when w0/λ is relatively small. The problem which results from θ→90° and the applicability of the nonparaxial vectorial moment theory as well as the possible method for solving the problem are discussed.
2006, 55 (9): 4569-4574.
doi: 10.7498/aps.55.4569
Abstract +
Based on the vectorial Rayleigh-Sommerfeld diffraction integrals, the closed-form expressions of vectorial nonparaxial circularly polarized Hermite-Laguerre-Gaussian (HLG) beams in the far-field are derived. The vectorial nonparaxial circularly polarized Gaussian beam is treated as a special case of our general formulae. The power in the bucket (PIB) is extended to the nonparaxial regime, where the intensity is replaced by the z component of the time-averaged Poynting vector, and used to characterize the beam quality of nonparaxial beams in the far field. Numerical calculation and analysis show the dependence of the PIB of vectorial nonparaxial HLG beams on the waist width-to-wavelength ratio w0/λ, as well as on the parameter α, mode indexes n and m, and bucket's size chosen.
2006, 55 (9): 4575-4581.
doi: 10.7498/aps.55.4575
Abstract +
The coherently coupled nonlinear Schrdinger (NLS) equation of the propagation of a light pulse in a fiber has been utilized. We have studied modulation instability of linearly polarized lights with near frequency not only in anomalous dispersion regime but also in normal dispersion regime in polarization-maintaining fibers, when the polarization direction along the two birefringence axes are orthogonal and the intensities along the two birefringence axes are equal. The results show that modulation instability can be produced both in anomalous and normal dispersion regimes. The input pulses have obviously different gain spectra when input power regime is different in normal dispersion regime. Furthermore, the gain spectra are different for different wave lengths (or different frequencies) when the power of input pulse is kept constant.
2006, 55 (9): 4582-4587.
doi: 10.7498/aps.55.4582
Abstract +
Achromatic retarder is a device to be used in wide spectral range for optical phase retardation. The phase retardation is constant when the wavelength is changed. Modern polarization technology and optical modulation demand high precision for the measurement of achromatic retarder. Based on the principle of polarizing modulation, this paper sets up an experiment system for measuring the phase retardation for high precision achromatic retarder of rhombic shape. The results indicate that the principle of high precision achromatic retarder is correct and the measurement error is less than 1%, it reaches a high precision and satisfies the requirement of application.
2006, 55 (9): 4588-4594.
doi: 10.7498/aps.55.4588
Abstract +
Multi-layer dielectric gratings for pulse compressor in high-energy laser system must provide high diffraction efficiency. In addition, its laser induced damage property is critical for the system. Nonuniform optical near-field distribution of multi-layer dielectric gratings is one of the important factors to limit its laser induced damage threshold. Electric field distributions in the grating region and multi-layer film region are analyzed by using Fourier modal method. Effects of grating structure on peak magnitude of electric field in grating ridge are analyzed when the top layer material is HfO2 and SiO2, respectively. The results show that there exists an optimum top layer thickness, at which the peak magnitude of electric field within grating ridge is a minimum. And the peak electric field in the grating ridge can be reduced by designing top gratings with high aspect ratio structure when top layer thickness is increasing. Finally, the peak electric field in the grating ridge can also be reduced when the multi-layer dielectric grating is used at big incident angle.
2006, 55 (9): 4595-4601.
doi: 10.7498/aps.55.4595
Abstract +
It is simulated numerically the transmission of beams phase modulated and spectrally dispersed by the unit for smoothing by spectral dispersion put in the laser driver for inertial confinement fusion. The results show that the diffraction spot of a spectrally dispersed beam becomes larger and its near-field uniformity is improved, while there exists area where the intensity is nearly even within the far-field spot. The effects of the main parameters of the electro-optic phase modulator and the grating in the unit on the diffraction characteristics of the beams are further discussed, and it is found that intensity modulation emerges in the far-field spot under some conditions.
2006, 55 (9): 4602-4607.
doi: 10.7498/aps.55.4602
Abstract +
The application of diffractive surface in the bifocal optical system is investigated by taking the advantage of the negative dispersion and the arbitrary phase modulation characteristics of binary elements, an analysis on the zoom equation is made and a sample design is presented. It is shown that good imaging quality can be achieved with the implementation of only four Germanium lenses. When the focal length of the system is 80 mm and the F-number is 0.8, the longitudinal aberration is less than 72 μm, the modulation transfer function (MTF) of 10 lp/mm is greater than 0.8 ；when the focal length is 160 mm and the F-number is 1.6, the longitudinal aberration is less than 35 μm, MTF of 10 lp/mm is greater than 0.7.
2006, 55 (9): 4608-4612.
doi: 10.7498/aps.55.4608
Abstract +
The diffraction electromagnetic field is calculated by rigorous coupled-wave theory for a binary metallic grating of nanometric dimensions. We discuss in detail the influence of the ratio of grating ridge width to grating period, the depth of groves and the angle of incident wave for the enhancement of diffraction electromagnetic field. Calculations for silver grating and gold grating result in some important conclusions.
2006, 55 (9): 4613-4617.
doi: 10.7498/aps.55.4613
Abstract +
In this paper, we report a pulsed digital micro-holography system for recording ultra-fast process of the order of femto-second. Two sub-pulse-train generators can be adjusted independently for generating reference beams with different spatial angles and object beams of the same angle, respectively, and the time delay between the sub-pulses can be adjusted from pico-senconds to femto-seconds. In the experiment, the ultra-fast dynamic process of air ionization induced by a femto-second laser pulse is recorded by the holographic recording system through spatially angular multiplexing, and both of the digitally reconstructed images in intensity and phase are obtained, which show the dynamic process of formation and propagation of the plasma with a time resolution of the order of femto-second.
2006, 55 (9): 4618-4623.
doi: 10.7498/aps.55.4618
Abstract +
Under the assumption of orthogonal electrical dipole moments of a cascade three-level atom with equally spaced energy levels, the full quantum theory is applied to study the emission spectrum of the atom interacting resonantly with a single-mode electromagnetic field in an ideal cavity. Spectral calculations for both the intensity-dependent and intensity-independent couplings are performed and the spectra in the cases of orthogonal dipole moments and parallel dipole moments are compared. It is found that some spectral lines disappear for the atom with parallel dipoles due to destructive interference leading to fewer lines compared with the spectrum of the atom with orthogonal dipole moments.
2006, 55 (9): 4624-4630.
doi: 10.7498/aps.55.4624
Abstract +
The fidelities of quantum states in the two-atom Tavis-Cummings model where the atoms are driven by an external classical field are derived. The influence of the external field and the dipole-dipole interaction of the atoms in a special initial state on the fidelity is discussd.
2006, 55 (9): 4631-4637.
doi: 10.7498/aps.55.4631
Abstract +
Quantum entanglement between a binomial field and a cascade three level atom is studied by using quantum entropy theory, and the influences of the initial state parameters of the field and the atom on the quantum entanglement are discussed. The results show that quantum entanglement of all states from the coherent state to number state interacting with a cascade three level atom can be displayed by using the binomial field property. Steady field-atom qutrit entanglement state can be prepared via the appropriate selection of system parameters.
2006, 55 (9): 4638-4641.
doi: 10.7498/aps.55.4638
Abstract +
The time dependent Schrdinger Equation of a laser-two-level-atom system has been solved by algebraic dynamics method. The exact analytical solution is obtained, and the single qubit logical gate can be realized through adjusting the amplitude and frequency of the single mode laser field as well as strength of the short pulse laser field.
2006, 55 (9): 4642-4646.
doi: 10.7498/aps.55.4642
Abstract +
We propose and demonstrate an improved differential phase shift key distribution scheme. Alice uses a pulsed laser source and two cascaded fiber loops to get coherent pulses, then modulates them randomly under differential phase shift scheme, which compensates for the random polarization mode dispersion and phase shift. An interferometer made up of two Faraday mirrors is employed to detect single photon under gate mode. In one-way transmission, QKD is free from Trojan attack. Our experiment at setup can work stably for a long time (at least 24h) with an error ratio of 3%. The stable scheme is efficient, economical and favorable for practical application.
2006, 55 (9): 4647-4651.
doi: 10.7498/aps.55.4647
Abstract +
In this paper, we investigate the entanglement dynamics of two entangled two-level atoms interacting with a single-mode field in a dissipative cavity. The results show that the evolution properties of the entanglement degree of two entangled atoms depend on the initial atomic entanglement degree and form, the average photon number of the cavity field, and the cavity leakage rate. When the atoms are initially in a particular entangled state, the degree of entanglement can be amplified and not influenced by the dissipation of the cavity field.
2006, 55 (9): 4652-4658.
doi: 10.7498/aps.55.4652
Abstract +
We study the steady and transient optical properties of electromagnetically induced transparency(EIT), spontaneous emission, and the photonic switching for a four-level atomic system embedded in photonic band gap(PBG) structures. The theoretical analysis shows that a special density of modes (DOM) can induce abnormal spectrum of absorption, dispersion，spontaneous emission and transient gain without inversion, and they can be controlled by an externally applied coherent light. Furthermore, we discuss the effects of the nonsingular DOM on the EIT windows and on the photon switch in detail.
2006, 55 (9): 4659-4664.
doi: 10.7498/aps.55.4659
Abstract +
An analytical model of passively Q-switched diode-pumped Er-Yb:glass laser with a Co2+:MgAl2O4 plate as a saturable absorber has been developed. Considering energy transfer between Er3+ and Yb3+, upconversion luminescence and the transition processes of the Co2+ in the Co2+:MgAl2O4 plate, rate equations of the passively Q-switched laser are presented and useful conclusions are drawn by numerical analysis in the paper. The model is very useful for optimizing these kind of lasers.
2006, 55 (9): 4665-4672.
doi: 10.7498/aps.55.4665
Abstract +
A concave mirror and a cat's eye reflector acting as a resonator mirror coustitute a cat's eye cavity. The parallelism of the incident and the reflected beams achieved by using three kinds of cat's eye reflectors (one ideal cat's eye reflector and two reflectors with errors), and the parameters of Gaussian beam in resonators which respectively use the three kinds of cat's eye reflectors are accurately calculated. We arive at the conclusion that for the Gaussian beam the cat's eye reflector is ideal and gives best parallelism of the incident and the reflected beam when the focal length of the convex lens, the radius of curvature of the concave mirror and the distance between them are equal. In this case the cat's eye cavity has the highest stability along with the largest fundamental mode volume and the least far-field divergence angle of fundamental mode. In the cavity design, one should strive to decrease the focal length of the convex lens in the cat's eye reflector and increase the radius of curvature of the output mirror. The influence on resonator performance when there are errors in the cat's eye reflector is also discussed. This paper gives a theoretical basis for the design of cat's eye cavity lasers.
2006, 55 (9): 4673-4678.
doi: 10.7498/aps.55.4673
Abstract +
The theoretical model based on the Fresnel diffraction integral is developed to describe the surface thermal lens (STL) signal excited by a cw modulated top-hat beam. The three-dimensional profile of temperature rise, the radial profile of the surface displacement and the diffraction signal of the probe beam obtained with both top-hat and Gaussian beam excitations are compared by numerical calculation. The dependence of the surface thermal lens amplitude on the experimental parameters are discussed. Numerical results show that the top-hat beam STL instrument is more sensitive than the Gaussian beam STL instrument, with a maximum sensitivity enhancement factor of approximately 2.
2006, 55 (9): 4679-4685.
doi: 10.7498/aps.55.4679
Abstract +
A clad-pumped short pulse Er3+/Yb3+-codoped fiber laser based on master oscillator and power amplifier (MOPA) structure, integrating the performances of broad-band tunable wavelength, uniform output power spectrum, high repetition rate and high average power to together, is proposed and demonstrated. Combining the cavity parameter optimization of the fiber master oscillator and power fiber amplifier with gain saturation characteristic of erbium-doped fiber, we achieved a lasing output with uniform output power and continuously tunable wavelength in the range from 1535 to 1530nm (i.e. 35nm band width). The maximum output power fluctuation is no more than 0.5 dBm, the average power is about 2 W, pulse repetition rate is greater than 10 GHz and pulse width is less than 30 ps in the whole tunable wavelength band width. Furthermore, the laser has advantages of good performance, simple all-fiber structure and convenient operation.
2006, 55 (9): 4686-4690.
doi: 10.7498/aps.55.4686
Abstract +
Using He-Ne laser, semiconductor laser，and Ar+ laser as the light sources, we observed the self-focusing phenomena of light wave at low power and the forming of spatial solitons in nematic liquid crystal. The spatial solitons with a length over five millimeters and multiple-mode spatial optical solitons were viewed. Furthermore, the forming conditions and characteristics of these solitons were also discussed.
2006, 55 (9): 4691-4694.
doi: 10.7498/aps.55.4691
Abstract +
The high order harmonic generation (HHG) of nitrogen molecule irradiated by ultra-intense femto-second pulsed laser is simulated by the time dependent density functional theory (TDDFT) method with the general gradient approximation of the exchange-correlation energy. The effect of different laser polarization direction on HHG is discussed. The results indicate that the HHG spectrum of N2 has similar characteristics as the typical atom HHG spectrum. With the increase of the angle θ between laser polarization direction and molecular axis, the spectral intensity of HHG decreases, which is in agreement with the experimental result by J.Itatanl published in Nature.
2006, 55 (9): 4695-4697.
doi: 10.7498/aps.55.4695
Abstract +
The positive and negative travelling wave solitons are predicted in photorefractive crystal biased by positive electric field in the low intensity regime. The amplitude and width of these solitons do not vary, showing the bright soliton properties, whereas the propagation properties of these solitons differ from previously observed steady-state photorefractive spatial solitons. These travelling wave solitons move on a straight line trajectory. The deflecting angle can be controlled by adjusting the parameter of the system.
2006, 55 (9): 4698-4703.
doi: 10.7498/aps.55.4698
Abstract +
In this paper a kind of high impedance substrate surface covered with different dielectric layer is analyzed by periodic moment method, their band-gap diagrams are described. Meanwhile, the propagating property of surface wave of the high impedance ground plane with different dielectric covering is tested, the results of theoretic analysis are validated. Our results can be helpful for the design of high impedance ground plane with a dielectric cover layer.
2006, 55 (9): 4704-4708.
doi: 10.7498/aps.55.4704
Abstract +
A novel displacement measurement with optical feedback of dual frequency laser has been put forward, which has been investigated both theoretically and experimentally. Intensities of the laser and the two orthogonally polarized modes are detected. It is found that the laser output power will be modulated when the object moves. When the displacement of the object is half wavelength, the signal of optical feedback has two peaks with the same depth of modulation. So the resolution of displacement sensor can be doubled. It is also found that when the object changes its moving direction, the order of intensity variation of the two modes will be changed. It can be used to judge the direction of the displacement. The simulation results are in good agreement with the experimental results. It is indicated that the sensor has advantages of simplicity, high resolution, direction identification cepability, large measurement range, operation in high optical feedback regime, and so on.
2006, 55 (9): 4709-4712.
doi: 10.7498/aps.55.4709
Abstract +
Based on the study of the metal-cladding waveguide on submillimeter scale, a new scheme for wavelength monitoring is proposed in this paper. The free space coupling technique is utilized to excite the ultrahigh-order mode to act as a probe, which is considered to be very sensitive to the wavelength change. It is experimentally demonstrated that a wavelength drift of 1pm is monitored.
2006, 55 (9): 4713-4719.
doi: 10.7498/aps.55.4713
Abstract +
We proposed a novel method to analyze the propagation of sub-picosecond optical pulses through semiconductor optical amplifiers(SOA), fully considering spectral dispersion of ultrashort pulses. A reasonable model is established via sampling the pulses simultaneously in time domain and frequency domain. Based on the established model, we observed an evident shift of the pulse spectrum, which agrees well with the experiment results in literature. Further, the relationship is discussed respectively between the value of shift and several external conditions, including wavelength, energy, width of the pulse, length of SOA and injected current. Gain suppression induced by ultrafast nonlinearities including carrier heating, spectral hole burning and two-photon absorption is described in detail, employing two-beam configuration. The simulated results give good guidance to the improvement of ultrafast dynamic characteristics of SOAs.
2006, 55 (9): 4720-4724.
doi: 10.7498/aps.55.4720
Abstract +
An all-fiber dynamic gain equalizer for flattening Er-doped fiber amplifiers based on a long period fiber grating (LPFG) with rotary refractive index change induced by high-frequency CO2 laser pulses is reported, for the first time to our knowledge. Experimental results show that its transverse load sensitivity is up to 0.37dB/(g·mm-1), which is 9 times higher than that of a normal LPFG induced by the same method. In addition, it is found that the strong orientation-dependence of the transverse load sensitivity of the normal LPFG reported previously has been weakened considerably. Therefore, such a dynamic gain equalizer based on the transverse load and temperature characteristics of this novel LPFG provides a much larger adjustable range and makes packaging of the gain equalizer much easier. A demonstration has been carried out to flatten an Er-doped fibre amplifier to ±0.5dB over a 32nm bandwidth.
2006, 55 (9): 4725-4728.
doi: 10.7498/aps.55.4725
Abstract +
Through calculation of intra-cavity dispersion of Ti:sapphire laser including air, we obtained super-continuum extending from 540 to 1030 nm using four-mirror cavity composed of proper chirped mirrors. The technique to generate an octave-spanning femtosecond pulse was further discussed.
2006, 55 (9): 4729-4733.
doi: 10.7498/aps.55.4729
Abstract +
The temporal dispersion effect and compensation approach of femtosecond laser scanning by an acousto-optical deflector (AOD) was studied. The group delay dispersion (GDD) of a single AOD at 800nm wavelength is about 9300fs2. Based on the principle of angular dispersion of AOD and the prism, an approach that uses single prism pre-compensating an AOD for the temporal dispersion was designed and demonstrated by experiments. At center frequency (70MHz) of the AOD, a 398fs pulse is compressed to 122fs, the range of pulse width on the entire bandwidth (50MHz—90MHz) is 120fs—180fs. This approach is demonstrated to be effective on compensation of temporal dispersion for AOD scanning femtosecond laser.
2006, 55 (9): 4734-4738.
doi: 10.7498/aps.55.4734
Abstract +
Filamentation with and without capillary restriction by focusing intense femtosecond pulses into the Argon-filled tube was experimentally studied in this paper. The results showed that the width of the broadened spectrum was affected by the input pulse energy and position of the capillary with respect to the filament. It was also indicated that the intensity of the short wavelength region of the spectrum was enhanced by the capillary restriction, which would be favorable to obtaining intense, monocycle pulses after compression.
2006, 55 (9): 4739-4743.
doi: 10.7498/aps.55.4739
Abstract +
All-fiber add/drop filter based on fiber-Bragg-grating (FBG) assisted coupler is compact and non-interferometric, which reduces the device's sensitivity to the grating position. By introducing the grating refractive modulation into the evanescent field coupling, the coupled-mode equation of FBG-assisted coupler is obtained and the influences of fiber mismatch on the filter spectra is investigated thoroughly. And a high-quality FBG-assisted filter is achieved by adjusting fiber structure parameters using asymmetric fused taper technology. The experimentally measured results are in good agreement with the numerical calculations.
2006, 55 (9): 4744-4747.
doi: 10.7498/aps.55.4744
Abstract +
We investigated theoretically and experimentally the acoustic waves tunneling and resonant-tunneling through one-dimensional phononic crystals within the frequency gap. The phononic crystal consists of parallel and periodically arrayed plastic plates immersed in water. Acoustic tunneling was observed for this single crystal structure at frequencies inside the band gaps. By slightly increasing the separation of the two plates in the middle, a double-crystal structure forms, which allows acoustic waves to resonantly tunnel through it, with transmission peaks observed inside the band gaps. At resonance, the measured group time is large, while off resonance very fast group velocity is found.
2006, 55 (9): 4748-4753.
doi: 10.7498/aps.55.4748
Abstract +
Experiments are performed to investigate the motion modes of granular particles contained in a vibrating narrow tube. It is found that the motion modes strongly depend on the bed thickness and vibration acceleration. Experiments show that in a container with small lateral size, convection rolls and arching of the particles can be confined. For the bed with sufficient thickness, a condensed state of particles always exists in the lower part of the bed, even when strong vibration is applied. Once a condensed state is formed, subharmonic bifurcations of the impact of granular particles at the container bottom can be observed. Experiments reveal that the bifurcation points are independent on the bed thickness. For shallow beds, the particles may be in condensed states or in convections, depending on the particle size.For spherical particles with a narrow size distribution, an ordered packing of the particles is observed. The packing consists of a concentric array of cylindrical “shells" of particles.In the “shell”, the particles are arrayed hexagonally.
2006, 55 (9): 4754-4759.
doi: 10.7498/aps.55.4754
Abstract +
The effect of granule velocity on the dilute-dense flow transition in granular system is studied both experimentally and by numerical simulations. Our experiments show that high granule velocity above the exit results in a decrease of critical exit size in dilute-dense flow transition if the inflow rate is fixed. When the granular flow becomes the dense flow, the effect of the granule velocity is counteracted by a high density region above the exit, and the outflow rate is almost irrelative with the granule velocity. Similar results are also obtained by molecular dynamics simulations for corresponding two-dimensional systems. With simulation calculations, the space distributions of the density and speed are also obtained. The distributions show that the density and the thickness of the granule accumulation above the exit vary with the incoming granule velocity, and the variation plays a key role in determining the final granular flow state.
2006, 55 (9): 4760-4766.
doi: 10.7498/aps.55.4760
Abstract +
In the paper, the meshless manifold method (MMM) is utilized to analyze transient deformations in dynamic fracture. The MMM is based on the partition of unity method and the finite coverage approximation which provides a unified framework for solving problems involving both continuums and dis-continuums. The method can treat crack problem easily because the shape function is not affected by the discontinuity in the domain. For localization problems at the tip of the discontinuity, these shape functions are more effective than those used in other numerical methods. The method avoids the disadvantages of other meshless methods in which the tip of a discontinuous crack is not considered. In meshless manifold method, the finite coverage approximation is used to construct the shape functions that overcome influences of the interior discontinuities in the displacement. Consequently, the meshless manifold method has some advantages in solving the discontinuity problems when the discontinuities are complex. When the dynamic fracture mechanics is analyzed by the MMM, the weak formulation of the partial differential equation for elastic dynamics is derived from the method of weighted residuals (MWR). The discrete space of the domain is used for the MMM. The Newmark family of methods is used for the time integration scheme. At last, the validity and accuracy of the MMM are illustrated by two numerical examples of which the numerical results agree with the analytical solution.
2006, 55 (9): 4767-4773.
doi: 10.7498/aps.55.4767
Abstract +
Initial stage of nano-void growth in single crystal copper under shock loading along direction has been investigated by using molecular dynamics (MD) simulation. The results show the void growth rate, represented by iucrease of equivalent radius of void vs time, keeps constant under certain shock strength. Two kinds of dislocation mechanisms of single void growth have been observed. When shock strength is lower than a critical value, dislocations nucleate and move outward only in the area around two vertices of the void along the shock direction and the void only grows along shock direction. When shock strength exceeds the critical value, dislocations nucleate and move outward not just in the above area but also in the equator perpendicular to the shock direction, and the void grows both along the shock direction and its normal. By examining the displacement history of atoms around the void surface, we find that the radial velocities of the vertices along and perpendicular to the shock direction almost keep constant during the tensile process. Based on constant radial velocities of vertices, we have derived a model of void growth which explains the constant void growth rate well.
2006, 55 (9): 4774-4782.
doi: 10.7498/aps.55.4774
Abstract +
Lattice Boltzmann method of two-and three-dimensional thermosolutal convection is investigated in this paper. Lattice Boltzmann method with multiple components was applied to simulate two-dimensional thermosolutal convection flow on a square cavity. The numerical results agree well with those of high order finite difference method. It shows that the numerical scheme is efficient. Therefore the lattice Boltzmann method is extended to investigate three-dimensional thermosolutal convection flow in cubic cavity. The comparison between the proposed lattice Boltzmann method and a finite difference method shows a satisfactory agreement. The limitation of the lattice Boltzmann model in the double-diffusive convection is discussed.
2006, 55 (9): 4783-4788.
doi: 10.7498/aps.55.4783
Abstract +
The oscillation property of a laser-induced cavitation bubble in a viscous fluid is investigated by a sensitive fiber-optic sensor based on optical beam deflection. The temporal and spatial evolutions of the bubble wall during the expansion and collapse are traced according to sequential waveforms induced by the bubble oscillation. Both the maximum and minimum bubble radii at each oscillation cycle are determined by experiment. Further, in combination with the theoretical analysis and numerical calculation, the variation of the maximum and minimum radii during oscillation and life-time of the bubble in different viscous fluids is obtained. The experimental results indicate that the liquid viscosity has an obvious influence on the bubble oscillation; larger viscosity makes the bubble contract more slowly, and the corresponding minimum radius and the bubble life-time become larger and longer, while the maximum radius is smaller.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2006, 55 (9): 4789-4794.
doi: 10.7498/aps.55.4789
Abstract +
According to the structure characteristic of the magnetically insulated transmission line oscillator (MILO), a one-sided multipactor discharge model is present. Through the calculations of the susceptibility curves and phase focusing effect, the physical conditions of the multipactor discharge occurring in the MILO are analyzed. The results show that one-sided multipactor modes have a wider phase focusing range than two-sided modes, and there is many chances for electronic grazing incidence on the metal surface for MILO. So the multipactor discharge is more serious for MILO than O-type devices.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2006, 55 (9): 4795-4802.
doi: 10.7498/aps.55.4795
Abstract +
The microstructure of CaO-Al2O3-SiO2(CAS)glass system is studied by molecular dynamics method.When Ca/Al equals to 1/2,which is called tectosilicate glass system,CAS is not a totally full network as conventional theories,but with some Non-Bridging Oxygen(NBO).The theoretical result proves Stebins's experimental conclusion.The result also reveals that when the ratio of Ca/Al is greater than 1/2 Al is preferred inserting in polymerized network to the end of polymerized network,when the ratio of Ca/Al is less than 1/2,the situationis is contrary.The “aluminium avoidance” principle believes that Al—O—Al linkages are energetically less favorable than Al—O—Si linkages in CAS glass system.However when the ratio of Ca/Al alters down across 1/2,there are some Al—O—Si linkages change to Al—O—Al and Si—O—Si linkages.
2006, 55 (9): 4803-4808.
doi: 10.7498/aps.55.4803
Abstract +
The selection of the flux and the design of the proper process are the key factors for the growth of Yb：KY(WO4)2 laser crystal. Yb：KY(WO4)2 crystal is grown by top seeded solvent growth (TSSG) method using K2W2O7 as a suitable flux. On the basis of TG-DTA, which has two obvious absorption peaks at 1045℃ and 1010℃, the Yb：KY(WO4)2 crystal's melting point is 1045℃, phase transition point from tetragonal system to monoclinic system is at 1040℃. Analyzing the X-ray diffraction spectrum of Yb：KY(WO4)2 crystal powder sample, we can conclude that the β-Yb：KY(WO4)2 crystal is of monoclinic system, and C2/c space group. The Yb：KY(WO4)2 crystals structure forms from the WO6 octahedra joined by WOOW double oxygen bridges and WOW single bridges. The IR and Raman spectra showed, the atom group WO6 has flex vibrations at 931cm-1，925cm-1, 891cm-1 and 840cm-1, and bend vibrations at 395cm-1，369cm-1，346cm-1 and 312cm-1, the WOOW double oxygen bridge has vibrations at 901cm-1, 759cm-1, 686cm-1, 435cm-1, 496cm-1 and 298cm-1, and the WOW single bridges has vibrations at 809cm-1, 525cm-1 and 235cm-1. At room temperature, the absorption peaks are at 940nm and 980nm the emission peaks are at 989nm—1030nm.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2006, 55 (9): 4809-4815.
doi: 10.7498/aps.55.4809
Abstract +
The electronic structure of pure and Mg-doped wurtzite ZnO has been investigated by using first-principles ultrasoft pseudopotential method in the generalized gradient approximation. The calculation indicates that the band gap of ZnO broadens with increasing Mg-doping concentrations. Our work shows that the bottom of conduction band is determined by the Zn 4s electron states which can shift to a higher energy due to Mg-doping.
2006, 55 (9): 4816-4821.
doi: 10.7498/aps.55.4816
Abstract +
We use the first-principles method to calculate the electronic band structures of MgCNi3. The calculated results show that the hybridization between C 2p and Ni 3d electron orbits leads to the planar characteristic of Ni 3d band. The Fermi level is located on the right slope of the van Hove singularity (vHs) peak. The high density of states (DOS) at the Fermi level with vHs and large magnetic fluctuations near the ferromagnetic phase transition point are the important factors for the superconductivity of MgCNi3. We study the variance of superconductivity and magnetism for three types of substitute doping in MgCNi3, and find that the electron doping moves the Fermi level to the lower DOS side, and transforms MgCNi3 to paramagneticm phase without superconductivity. The inter-metal compounds with the same valence electrons doping change the shape of Fermi surface, resulting from the hybridization between atoms. The decrease of the DOS decreases their superconductivity. The hole doping enhances the DOS at the Fermi level on the peak of vHs, but the large magnetic exchange interactions induce the ferromagnetic order, and the superconductivity disappears abruptly.
2006, 55 (9): 4822-4827.
doi: 10.7498/aps.55.4822
Abstract +
Using the density-functional theory in combination with nonequilibrium Green's function technique, we studied the densities of states and transport properties of the(7，0)—(8，0)and(8，0)—(9，0)single-wall carbon-nanotube heterojunctions containing one pentagon-heptagon-pair (5/7) topological defect. The result suggests that the effect of pentagon-heptagon-pairs (5/7) topological defects on carbon nanotubes is remarkable.In addition, the heterojunctions constituted by different types of carbon nanotubes also have different characteristics.
2006, 55 (9): 4828-4836.
doi: 10.7498/aps.55.4828
Abstract +
A magnon-phonon interaction model is developed on the basis of two-dimensional square Heisenberg ferromagnetic system. The transverse acoustic phonon excitation is studied through Matsubara Green function theory, and the transverse acoustic phonon dispersion curve is calculated at the main symmetric point and on the symmetric line in the first Brillouin zone. It's found that on the line Σ in first Brillouin zone, there is hardening for the transverse acoustic phonon in the smaller wave vector zone (point Γ near kxa＜0.2), but there is softening for the transverse acoustic phonon in the softening zone (0.25＜kxa＜0.7), there is hardening for the transverse acoustic phonon at point M near (0.75＜kxa). On the line Δ, there is no phonon softening and hardening for transverse acoustic phonon. On the line Z, there is softening for transverse acoustic phonon in smaller wave vector zone (point X near kxa＜0.65), but there is hardening for the transverse acoustic phonon at the point M nearby. The influences of different parameters on the transverse acoustic phonon excitation are also illustrated. It's found that the coupling of the magnon-phonon coupling and the spin wave stiffness are the main factors affecting the transverse acoustic phonon softening.
2006, 55 (9): 4837-4842.
doi: 10.7498/aps.55.4837
Abstract +
Multiple-doped skutterudites SmmCenFe1.5Co2.5Sb12 were prepared by melting and spark plasma sintering method, and the effects of doping atoms Sm and Ce on the thermoelectric properties of these compounds were investigated. For p-type SmmCenFe1.5Co2.5Sb12, with the Sm and Ce multiple-doping amount increasing, the electrical conductivity and the thermal conductivity decrease and the Seebeck coefficient increases. When the doping amount is similar, in comparison with the Sm or Ce doping, the Sm and Ce multiple-doping can lower the thermal conductivity of skutterudites 10%—40%. At 775K, the ZTmax value of 0.84 was obtained for Sm0.22Ce0.20Fe154Co2.46Sb11.89.
2006, 55 (9): 4843-4848.
doi: 10.7498/aps.55.4843
Abstract +
The powders of p-type pseudo-ternary Sb2Te3-Bi2Te3-Sb2Se3 thermoelectric materials prepared by mechanical alloying method were analysed by XRD, with Te，Bi，Sb and Se element granules alloyed after 100h ball milling. The alloyed powders were analysed by SEM, showing granules of fine powders about 10—100nm in size. Blocks of p-type pseudo-ternary thermoelectric materials were prepared with the powders by cold-pressing and sintering. Seebeck coefficient and electrical conductivity for samples with different sintering temperatures were measured at room temperature. The results suggest that thermoelectric properties gradually improve with sintering temperatures during 300℃, the power factor enhances from 0.59μW cm-1K-2 of unsintered samples to 15.9μW cm-1K-2 of samples sintered at 300℃. So the result might play an important role in optimizing sintering temperature.
2006, 55 (9): 4849-4853.
doi: 10.7498/aps.55.4849
Abstract +
N-type (Bi2Te3)0.93(Bi2Se3)0.07 thermoelectric materials doped with various content of TeI4 (0, 0.05, 0.08, 0.10, 0.13, and 0.15wt%) have been fabricated through the combination of zone melting and spark plasma Sintering. Electrical conductivity (σ), Seebeck coefficient (α) and thermal conductivity (κ) were measured in the temperature range of 300—500K. The influence of the variation of TeI4 content on thermoelectric properties was studied. The increase of TeI4 content caused an increase of carrier concentration and thus resulted in an increase of σ and a decrease of α, and the lattice thermal conductivity was decreased by the increase of phonon scattering resulting from heterogeneous ion (I) scattering and carrier scattering. The maximum figure of merit ZT (ZT=α2σT/κ) of the sintered materials in the direction perpendicular to the pressing direction showed a value of 0.92 for the sample containing 0.08wt% TeI4. In addition, the bending strength of the sintered materials was improved to about 80MPa from about 10MPa of the zone-melted ingot, which is of advantage to the fabrication process and the improvement of the reliability for thermoelectric modules.
2006, 55 (9): 4854-4859.
doi: 10.7498/aps.55.4854
Abstract +
Intrinsic SnO2 films as the high resistance transparent (HRT) layers are prepared by ultrasonic spray pyrolysis and used in CdS/CdTe solar cells with a thin CdS layer. XRD and AFM are used to study the performance of the thin CdS layers. The illuminated and dark I-V characteristics, spectral response (SR) and C-V characteristics of the devices are measured. The results show that the thin CdS films deposited on HRT layers have an obvious preferred orientation along (111) plan. But pinholes are formed when using a thin CdS layer. After introducing the HRT layer, the tunneling leakage caused by the pinholes can be avoided, which effectively protects the p-n junction. Meanwhile, higher shunt resistivity, fill factor, short-wave response, carrier concentration and lower dark saturation current density have been achieved. As a result, the conversion efficiency is enhanced by 14.4%.
2006, 55 (9): 4860-4864.
doi: 10.7498/aps.55.4860
Abstract +
ZnSe-based organic-inorganic heterostructure diodes in which ZnSe layer was fabricated by electron-beam evaporation were studied. Electroluminescence from ZnSe peaking at 578nm was observed from bilayer device ITO/ZnSe(50nm)/Alq3(12nm)/Al, but it is difficult to observe any EL emission from single-layer diode ITO/ZnSe(50—120nm)/Al. Based on this, we further introduced a PVK or NPB hole-transporting layer (HTL), to make trilayer devices ITO/HTL/ZnSe/Alq3/Al to investigate the influence of ZnSe layer on the emission of the trilayer devices by varying the device structure. Our experimental data of EL emission confirm the roles played by ZnSe in these devices of transporting not only electrons but also holes, as well as acting as an emissive layer. Furthermore, a luminescence mechanism of charge carriers injection luminescence in ZnSe layer is suggested.
2006, 55 (9): 4865-4872.
doi: 10.7498/aps.55.4865
Abstract +
In this paper, within the frame of Green's function theory, we study the magnetic and thermodynamic properties of the mixed-spin antiferromagnet Y2BaNiO5 in the spin-1 one-dimensional anisotropic Heisenberg model. We find the correlation function, low-lying excitation, ground-state energy, specific heat and static susceptibility of Y2BaNiO5 for different values of exchange anisotropic parameter γ, and the results are in good agreement with experimental and numerical results.
2006, 55 (9): 4873-4877.
doi: 10.7498/aps.55.4873
Abstract +
Nanoscale C and SiC doped MgB2 tapes were prepared by the in situ powder-in-tube method. The samples were characterized using X-ray diffraction, scanning electron microscope, superconducting quantum interference device magnetometer etc. Transport JC and its magnetic field dependence were evaluated by a standard four-probe technique. It is found that JC for all the C and SiC doped tapes was significantly enhanced in magnetic fields up to 14 T compared to the undoped ones. For the 5% C and SiC doped samples, at 4.2 K and 10 T, JC increased by a factor of 32 and 26, respectively. The improvement of JC-B properties in C and SiC doped MgB2 tapes is attributed to good grain linkage and the introduction of effective flux pining centers with the doping. Furthermore, our results clearly prove that the observed positive effects after mixing with SiC are nothing else than the result of the decomposition of this compound and substitution of carbon for B in MgB2.
2006, 55 (9): 4878-4882.
doi: 10.7498/aps.55.4878
Abstract +
This study is about carbon-nanotube (CNT)-doping of MgB2 superconductor processed under the magnetic field. The Jc(H) for CNT doped sample increased by a factor of 2—3 in low filed and more than an order of magnitude in high field after processing in magnetic field. The alignment of CNT along the processing field direction was observed by SEM.
2006, 55 (9): 4883-4887.
doi: 10.7498/aps.55.4883
Abstract +
The ferromagnetic shape memory alloy Mn2NiGa was developed recently. In order to improve the properties of this material and develop new ferromagnetic shape memory alloys, in this work an experiment of partially substituting Fe or Co for Ni in Mn2NiGa alloys was carried out to examine the effect of Fe or Co in quaternary Mn50Ni25-xFe(Co)xGa25 alloys on their structure, magnetic properties, martensitic transformation, and mechanical properties. Some interesting results were presented in this paper.
2006, 55 (9): 4888-4892.
doi: 10.7498/aps.55.4888
Abstract +
The s=1/2 quasi-one-dimensional Heisenberg antiferromagnetic chain with asymmetrical sublattices possesses three branches of spin-wave spectra (one in acoustic mode and the other two in optical mode). The frustration relieves the gap-degeneracy of two optical branches and softens the spectrum in acoustic mode, but doesn't soften the spectra in optical mode. Also, the frustration moves down obviously one of the two spectra in optical mode. It means that the frustration makes the spin-wave excitation described by spectrum in optical mode easier and more important. The status of spin on the chain changes more easily than that of side spin under the effect of frustration. The weakening of magnetic order in ground state becomes strong with the strengthening of frustration. By comparison with numerical results of exact diagonalization and DMRG methods, we discuss the merit and drawbacks of the spin-wave approximation.
2006, 55 (9): 4893-4900.
doi: 10.7498/aps.55.4893
Abstract +
Microstructure, magnetic and electronic transport properties of the inhomogeneous system 1/m Ag2O-La0.833K0.167MnO3 (1/m is molar ratio, m=32, 16, 8, 4, and 2) have been studied. X-ray diffraction patterns show that all the samples are the two-phase composite and consist of a magnetic La0.833K0.167MnO3 (LKMO) perovskite phase and a nonmagnetic metal Ag phase. The room temperature magnetoresistance (MR) effect is enhanced significantly due to the addition of Ag. For the m = 4 sample the MR ratio increases from 10% of the pure compound LKMO to 32% under a lower field of 0.5 T and from ～35% of LKMO to 64 % under a higher field of 5.5 T at the temperature of 300 K. In the low temperature range from 4.2 K to 265 K, however, the MR ratio of the Ag-doped sample decreases with increasing the Ag content in the samples. The effect is discussed qualitatively by use of the relative change among the intrinsic MR effect and the extrinsic MR effect including the spin-polarized-tunneling and spin-dependent scattering effects at grain boundaries.
2006, 55 (9): 4901-4905.
doi: 10.7498/aps.55.4901
Abstract +
Using the renormalization-group transformation and cumulative expansion technique, the phase transition and critical properties of the S4 model on a special diamond-type hierarchical lattice are studied, and its fixed points and critical exponents are obtained. The results show that there exists a Wilson-Fisher fixed point besides the Gaussian fixed point, and compared with the Gaussian model of the special diamond-type hierarchical lattices, the critical exponents have changed.
2006, 55 (9): 4906-4911.
doi: 10.7498/aps.55.4906
Abstract +
The structure and magnetic properties have been investigated by means of X-ray diffraction and magnetization measurements. The Er2AlFe16-xMnx (x=1, 2, 3, 4, 6 and 8) compounds have a hexagonal Th2Ni17-type structure. The thermal expansion of Er2AlFe16-xMnx (x=1, 2, 3, and 4) compounds have been investigated by X-ray dilatometry in the temperature range 103—654K. The results show that there is a thermal expansion anomaly at low temperature and a negative thermal expansion near the Curie temperature. There exists a strong and anisotropic spontaneous magnetostriction in the magnetic state of Er2AlFe16-xMnx compounds. The spin reorientation at low temperature results in an enhancement of the spontaneous volume magnetostrictive deformation of Er2AlFe16-xMnx compounds. Magnetization measurement shows that the Curie temperature and the spontaneous magnetization at 5K of Er2AlFe16-xMnx compounds decrease rapidly with increasing x, and that the Mn substitution for Fe results in obvious change of the magnetic anisotropy.
2006, 55 (9): 4912-4917.
doi: 10.7498/aps.55.4912
Abstract +
The investigation on the structure, resistivity and susceptibility was carried out for Eu2-xPbxRu2O7 (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0 and 1.8) samples. It is found that the resistivity of the samples, the local magnetic moment of Ru4+ and the freezing temperature TG of spin glass decrease gradually with the increasing substitution concentration value x of Pb for Eu in Eu2-xPbxRu2O7 system. A metal-insulator (M-I) transition occurs near x=0.8. It is suggested that in this system the partial substitution of Pb2+ for Eu3+ results in the increasing of carrier concentration. And the mixing of 6p band of Pb and the t2g band of Ru 4d electrons brings about an enhancement of itinerary for Ru 4d electrons.
2006, 55 (9): 4918-4922.
doi: 10.7498/aps.55.4918
Abstract +
The negative refraction phenomenon in wavy two-dimensional (2D) photonic crystals (PC) is investigated with the iso-frequency surfaces of PC and incident medium. The finite-difference time-domain method is used to simulate the negative refraction of incident Gaussian beam with different wavelengths and incident angles. When the incident angle is set at 45 degrees, the linear relation exists between the negative refraction angle and the wavelength within the range from 1485 to 1530nm, which is suitable for the superprism effect. In order to increase the transmission when negative refraction happened at large incident angles, interface projection method is employed.
2006, 55 (9): 4923-4927.
doi: 10.7498/aps.55.4923
Abstract +
Ag films with different thickness from 8.2nm to 107.2nm were prepared by DC sputtering deposition and analyzed by X-ray diffraction with the help of optimization program on computer. Microstructrue analysis shows that the films are made of fcc-Ag particles. With the increase of thickness, the mean size of Ag particles increases and the interplaner spacing decreases gradually. The optical constants computed by computer program shows that n value decreases quickly with the increasing thickness below 17.5nm and k value changes in reverse, and then go steadily when the thickness is larger than 17.5nm at the wavelength of 550nm.
2006, 55 (9): 4928-4933.
doi: 10.7498/aps.55.4928
Abstract +
Fully occupied ferroelectric ((KxNa1-x)0.4(SryBa1-y)0.8, 0.5051 of KNSBN films can be greatly improved by introducing alkali metal ions, the measured values of transverse electro-optic coefficient r51 of K0.2Na0.2Sr0.24Ba0.56Nb2O6, K0.2Na0.2Sr0.6Ba0.2Nb2O6, K0.2Na0.2Sr0.72Ba0.08Nb2O6 are 108.52pm/V, 119.98pm/V, and 126.96pm/V, respectively. An enhancement of r51 with Sr2+content in KNSBN films has been demonstrated.
2006, 55 (9): 4934-4939.
doi: 10.7498/aps.55.4934
Abstract +
Piezomodulated reflectance (PzR) spectra have been measured for two samples of InAs surface quantum dots (SQDs) deposited on GaAs (311)B substrates with In0.35Ga0.65As template. At 77K multiple confined-state SQDs transitions can be clearly resolved from the PzR spectra . The detailed optical transition features of SQDs, QDs buried by capping layer, In0.35Ga0.65As template and GaAs substrate layers were obtained from well-fitted PzR spectra using the first or third derivative of a Lorentz line shape. Differences between PzR results of two samples were discussed qualitatively.
2006, 55 (9): 4940-4945.
doi: 10.7498/aps.55.4940
Abstract +
Eu3+ doped Sr2CeO4 samples were prepared by a solid-state method and the luminescent properties of the samples with and without adsorbed moisture were investigated. When the Sr2-xEuxCeO4+x/2 samples were prepared, it was found that only the excitation energy in the strong charge-transfer-state (CTS) band of Ce4+—O2- peaking at about 35700cm-1 was transferred to Eu3+ion while that in the weak CTS band of Ce4+—O2- located at about 29400cm-1 led to Ce4+—O2- charge-transfer (CT) emission. After adsorption of moisture in the Sr2-xEuxCeO4+x/2 samples, the intensity of Eu3+intra-4f6 absorption transition increased remarkably, the energy transfer took place from the two Ce4+—O2- CTS bands to Eu3+ ion. The excitation energy in the strong Ce4+—O2- CTS band was transferred to the Eu3+—O2- CTS band through radiationless process involving exchange interaction, however, the weak Ce4+—O2- CTS band caused the excitation to the Eu3+ excited levels through resonance radiationless process by a multipole interaction mechanism.
2006, 55 (9): 4946-4950.
doi: 10.7498/aps.55.4946
Abstract +
The preparation and the luminescent properties of green-emitting phosphor Ca3SiO5:Eu2+ have been studied. The broad green emission band with the peak located at 502 nm which consists of a main and a subsidiary emission peak at 501nm and 570nm，respectively， originate from the centers of Eu2+ ions. There are two different Eu2+ emitting centers in Ca3SiO5:Eu2+, which has been confirmed by the experiment results and empirical formula of Van Uitert，and the Eu2+ ions occupy Ca2+ sites with coordination number 8 and 4 in this phase. The excitation spectra extend from 250 nm to 450 nm and the excitation peak positions are located around 375 nm. The phosphor can be excited effectively by InGaN chip emitting in the range of 350—410 nm.
2006, 55 (9): 4951-4955.
doi: 10.7498/aps.55.4951
Abstract +
We investigated the optical and electrical properties of Mg-doped InxGa1-xN(0≤x≤0.3) grown by metalorganic chemical vapor deposition with different In and Mg contents. When the Mg doping concentration was fixed, the hole concentration of samples increased remarkably with the elevation of In mole fraction. The highest hole concentration achieved was 2.4×1019cm-3,the doping efficiency increased nearly by two orders. We explained the carrier transition mechanism with the help of the photoluminesce spectra. In addition, we obtained the activation energy of Mg and the band position of deep donor in InGaN:Mg samples.
2006, 55 (9): 4956-4961.
doi: 10.7498/aps.55.4956
Abstract +
The 0.1 mol% Er3+-doped Al2O3 and SiO2-Al2O3 powders have been prepared by the sol-gel method. The results show that the addition of 5 mol% SiO2 into the Er3+-doped Al2O3 suppresses the phase transitions of γ→θ and θ→α. For the 0.1 mol% Er3+-doped Al2O3 powders at the sintered at temperature of 900℃, the broadband photoluminescence (PL) spectrum centered at 1.53 μm in the range from 1.47 μm to 1.63 μm was obtained with the full width at half maximum of 56 nm, and the splitted PL spectra appeared for powders sintered at 1000—1200℃. For the 0.1 mol% Er3+-doped Al2O3-SiO2 powders, the PL spectrum has a single broadband centered at 1.53 μm even when the sintering temperature is as high as 1200℃, and the PL intensity increases by one order of magnitude, because—OH group in the Al2O3-SiO2 powders has been removed completely, compared with that in the Al2O3 powders with and without mixing of SiO2 sintered at the temperature of 900℃.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2006, 55 (9): 4962-4967.
doi: 10.7498/aps.55.4962
Abstract +
Based on the flat-topped beams model proposed by Li and the propagation theory of partially coherent light, the spectrum analytical expression of partially coherent flat-topped beams propagating in the linear gain or loss media was derived and the spectral properties were studied quantitatively by numerical calculation. The variation characteristics of the on-axis spectrum in near- and far-field regions have been discussed in details. The effects of the property of the linear gain or loss media and some parameters of the light source, such as the central frequency, spectrum width and spatial coherence parameter on the spectral shift have also been discussed. It can be shown that the light source parameters have greater effects on the value of the frequency shift than on the total changing trend of the spectrum along the propagation distance, whereas the latter is determined by the beam order of flat-topped beam.
2006, 55 (9): 4968-4973.
doi: 10.7498/aps.55.4968
Abstract +
The propagation properties of one-dimensional off-axis Gaussian beams through the turbulent atmosphere are studied in detail. The propagation equation of intensity is derived. It is shown that one-dimensional off-axis Gaussian beams in turbulent atmosphere undergo three stages of evolution with increasing propagation distance z, i.e., their saw-tooth beam profile is similar to the initial one in the near field, then becomes a flat-topped profile with increasing z, and at last turns into Gaussian-like profile in the far field. The turbulence accelerates the evolution of the stages which one-dimensional off-axis Gaussian beams undergo. Furthermore, the normalized intensity distributions of one-dimensional off-axis Gaussian beams with different beam numbers become close to each other due to turbulence. In addition, one-dimensional off-axis Gaussian beams with higher beam numbers are less sensitive to the effects of turbulence than those with lower beam numbers, and one-dimensional off-axis Gaussian beams are less sensitive to the effects of turbulence than Gaussian beams.
2006, 55 (9): 4974-4979.
doi: 10.7498/aps.55.4974
Abstract +
We numerically simulated the chemical process and one-dimensional diffusion process in atmospheric plasmas. We deduced the three-component (electrons, positive ions and negative ions) ambipolar diffusion formulas, observed the spatial separation of various components in the diffusion process, and showed the influence of diffusion and chemical processes on the temporal evolutions of the electron number density.
2006, 55 (9): 4980-4982.
doi: 10.7498/aps.55.4980
Abstract +
If the situation of quantum gravity nowadays is nearly the same as that of quantum mechanics in its early time of Bohr and Sommerfeld, then a first-step study of the quantum gravity under Sommerfeld's quantum condition of action might be helpful. We present the spectra of quantum Schwarzschild black hole in non-relativistic quantum mechanics. It is found that the quantum of area is 8π3l2p, the quantum of entropy is 2π3kB, and the Hawking evaporation will cease when the black hole reaches the ground state m=123mp. A very natural conjecture is that the constituents of dark matter may come from the remnant (relics) of primordeal black hole with life time smaller than that of the universe.
