Vol. 58, No. 3 (2009)
The expansion of orthogonal complete set and transformation operator in the teleportation of a three-particle entangled W state
2009, 58 (3): 1371-1376. doi: 10.7498/aps.58.1371
Firstly，we discuss a scheme for teleportation of a three-particle entangled W state via a two-particle and a three-particle entangled state. Then，in accordance with the principle of superposition and transformation operators，the three-particle entangled W state is expanded by Bell bases and the teleportation can be realized. The relation of transformation operators with unitary operation is discussed. The necessary condition for realizing the teleportation is that the transformation operators have inverse operators.
2009, 58 (3): 1377-1382. doi: 10.7498/aps.58.1377
Using a single-mode laser cubic model driven by additive colored noise and multiplicative colored noise，through theory of Novikov，Fox approximation and the approximation of Stratonovich，an expression of intensity correlation function C was reached at. The effects of the correlation time τ，the net gain a0 and the cross-correlation intensity λ on the intensity correlation function C was investigated. The result of numerical simulation shows that the intensity correlation function C increases with the correlation time τ for the net gain above the threshold （a0>0），but decreases as correlation time increases for the net gain below the threshold （a0C decreases as cross-correlation λ intensity increases no matter the net gain is above or below the threshold. The curve of C versus a0 has a single peak.
On the basic of bipartite networks，bielemental networks are defined as networks which include two kinds of vertexes，and connections between different kinds of vertexes are permitted. In this article，a bielemental random network model is founded，and the structure of the bielemental random network is studied. Small-world effect can be found in such model，furthermore，the average shortest path length is smaller than that of unipartite random networks. And the proportion of the numbers of two kinds of vertexes is a very important factor.
2009, 58 (3): 1391-1395. doi: 10.7498/aps.58.1391
By means of an extended colored-noise approximation，we investigated the effects of asymmetry of the potential and noises on the mean first-passage time T+（xs1→xs2） and T-（xs2→xs1） in two opposite directions in an asymmetric bistable system （here xs1 and xs2 are stable points of the asymmetric bistable system）. Numerical results show that T+（xs1→xs2） decreases with increasing of τ1 （the correlation time of multiplicative noise） and τ2 （the correlation time of additive noise）. T-（xs2→xs1） increases with increasing of τ1 and τ2. The curves of T+（xs1→xs2） versus λ and T-（xs2→xs1） versus λ are single-peaked. T+（xs1→xs2） will increase when r increases，but T-（xs2→xs1） will decrease when r increases.
The steady state probability distribution and mean first passage time of FHN neural system driven by non-Gaussian noise
2009, 58 (3): 1396-1402. doi: 10.7498/aps.58.1396
We investigated the FitzHugh-Nagumo neural system driven by non-Gaussian noise. The expressions of the stationary probability distribution and the mean first-passage time are obtained through the path-integral approach and the unified colored noise approximation. The results show that the intensity of additive noise can induce phase transition，while the intensity of multiplicative noise，the derivation parameter and the correlation time cannot. The non-Gaussian noise shortens transformation time between resting state and excited state and is beneficial to transmission of information in neural system.
Effect of the period modulation of the correlation intensity between color noises on the stochastic resonance of the single-mode laser with the signal modulation
2009, 58 (3): 1403-1409. doi: 10.7498/aps.58.1403
For the laser system in which the correlation intensity between color noises is modulated by the time period，we investigate the stochastic resonance with the signal modulation of the noise. By means of the linear approximation，we calculate the intensity correlation function and signal-to-noise ratio （SNR） and discuss the evolution of the SNR with the noise intensity and self-correlation time of noises and signal frequency and time period modulation frequency. A new stochastic resonance is found. The evolution of the signal-noise ratio with the time period modulation frequency reveals periodic oscillation. We obtain the generalized stochastic resonance, in which the evolution of the signal-noise ratio with the self-correlation time of the pump noises and signal frequency presents the stochastic resonance. The typical stochastic resonance of the signal-noise ratio with the noise intensity is obtained also. The evolution of the signal-noise ratio with the self-correlation time of the quantum noise shows the restrainment.
2009, 58 (3): 1410-1419. doi: 10.7498/aps.58.1410
A fuzzy boundary modular neural network （FBMNN） is proposed for the chaotic time series prediction. First，the reconstructed phase space is divided into several subspaces and the divided points are evaluated by genetic algorithms. Then a fuzzy membership function is defined and the fuzzy boundary is set on the border according to the fuzzy membership. Through this fuzzy treatment，the jumping problem of the predicted data near the divided points are solved. Finally the data points of each module and its fuzzy boundary are input to a recurrent neural network for training and the output predicted points are synthesized by a synthesis forecast module. The effectiveness of FBMNN is evaluated by using three benchmark chaotic time series data sets：the Mackey-Glass series，Lorenz series，and Henon series. The simulation results show that FBMNN improves the performance of chaotic time series prediction.
2009, 58 (3): 1420-1431. doi: 10.7498/aps.58.1420
By extending the square map，a one-dimensional generalized square map with exponential term is constructed，and its corresponding two-dimensional map is obtained via one-order coupled item in this paper. By using the one-parameter bifurcation diagram，two-parameter dynamics behavior distribution diagram，iterative mapping curve and attractor phase graphics，these generalized square maps are analyzed and simulated. The research results indicate that one-dimensional generalized square map distributes in the unit region and has the nonlinear dynamical phenomenon similar to single-peak square map，and two-dimensional generalized square map has the phenomenon of Hopf bifurcation and locked-frequency shown with complex，flexible and strange-shaped limit cycles and chaotic attractors.
2009, 58 (3): 1432-1440. doi: 10.7498/aps.58.1432
The permanent magnet synchronous motor （PMSMs） may have chaotic behaviors under certain working conditions, especially for uncertain values of parameters，which threatens its secure and stable operation. Hence，it is important to study methods of controlling or suppressing chaos in PMSMs. In this paper，the Takagi-Sugeno fuzzy control model for PMSMs with parameter uncertainties is established via the Takagi-Sugen modeling method. Based on the new model，the control conditions of asymptotical stability for PMSMs with parameter uncertainties have been derived by Lyapunov method and matrix analysis. An illustrative example is also given to show the effectiveness of our results. Compared with the curently available results，the obtained results exhibit some advantage.
Adaptive synchronization between different fractional hyperchaotic systems with uncertain parameters
2009, 58 (3): 1441-1445. doi: 10.7498/aps.58.1441
This paper addresses parameter identification and the adaptive synchronization between fractional CYQY hyperchaotic system and fractional Lorenz hyperchaotic system with uncertain parameters. Based on fractional stability theory，an adaptive controller and the paramter updating rule are designed. Numerical simulation shows the effectiveness of the adaptive controller.
2009, 58 (3): 1446-1455. doi: 10.7498/aps.58.1446
A new four-dimensional chaotic system is reported in this paper. Basic dynamic properties of the new system are investigated via theoretical analysis，numerical simulation，Lyapunov exponent，Lyapunov dimension and Poincare diagrams. Finally the chaotic circuit is designed and realized by the Multisim software. It confirms that the chaotic system is different from the exisiting chaotic systems and is a new hyperchaotic system.
2009, 58 (3): 1456-1461. doi: 10.7498/aps.58.1456
This paper studies the fractional-order Lü system which has been presented recently，and designed an electronic circuit to realize it. The hyper-chaotic behavior of the fractional-order Lü system is verified by numerical simulation and circuit experiment. Based on the stability theory of the fractional-order system，a simple linear feedback controller is designed to make full states of a fractional order Lü system to track control sinusoidal waves or arbitrarily fixed point. The simulation results are presented to demonstrate the effectiveness of the proposed method.
2009, 58 (3): 1462-1466. doi: 10.7498/aps.58.1462
A method of chaos synchronization of a complex network with different nodes is proposed. The complex network is constructed by chaos systems with diverse structures. The coupling functions of the connected nodes of the complex network are identified based on Lyapunov stability theory. The Rssler system，Coullet system and Lorenz system are taken as network nodes of the complex network in the paper. Simulation results show that a stable synchronization is obtained in whole complex network. The method can achieve synchronization of the networks with nodes of any chaotic systems，and the number of the node does not affect the stability of the whole complex network，therefore，it has a universal application.
A secure communication scheme based on parameter identification of first order time-delay chaotic system
2009, 58 (3): 1467-1472. doi: 10.7498/aps.58.1467
Based on parameter modulation theory，a parameter observer is designed for the first order time-delay Logistic chaotic system. The unknown parameter of this system can be identified by transmitting a single signal，then the useful signal modulated in the parameter will be recovered successfully. By choosing different frequency signals as “0" and “1"，a practical digital secure communications scheme is designed. Numerical simulation shows the effectiveness of the method.
2009, 58 (3): 1473-1479. doi: 10.7498/aps.58.1473
The system composed of Rydberg Li atom in an electric field is chaotic because of the core scattering. The period orbits and the closed orbits both exist near the saddle point. The dynamics of this system is studied with the closed-orbit-theory and Poincaré SOS method. The relations of the two methods are discussed for the first time and new information is obtained which can't be retrieved from the recurrence spectra.
2009, 58 (3): 1480-1483. doi: 10.7498/aps.58.1480
Based on the rate equations describing the dynamic characteristics of the master and slave vertical cavity surface emitting laser （M-VCSEL，S-VCSEL）, under the modulation of pulsed bias current，the polarization characteristics of M-VCSEL output and the polarization switching performance of S-VCSEL subjected to optical pulse output from the M-VCSEL have been investigated. The results show that periodical pulses can be obtained by adding a periodical pulsed current on the M-VCSEL. Under injection of the optical pulsed from M-VCSEL, the output power of S-VCSEL will switch periodically between two orthogonal polarizations，and the period is equal to the period of the modulated current in M-VCSEL. Through changing the modulated amplitude of current in M-VCSEL，the orthogonal polarization suppression ratio （OPSR） can be controlled easily.
2009, 58 (3): 1484-1490. doi: 10.7498/aps.58.1484
The chaotic communications systems with optical feedback lasers in strong injection and open-loop configuration are studied in this paper. The quantity relationship between gain and injection factor is obtained by numerical calculation. The demodulators performances under the conditions of whether the gain is used to adjust the output of the receiver are compared. The result indicates that the recovered message is more close to the original message by using the adjusted subtraction demodulation method. It is proved that message rate has no effect on gain by testing sine signals with different rates. Further，the gain is shown to be independent of message type and encryption mechanism by testing digital signals at 0.2?Gbit/s rate.
2009, 58 (3): 1491-1496. doi: 10.7498/aps.58.1491
The simple model of discrete excitable medium is applied. In order to make spiral wave meander，we introduce some death cells and fatigue cells into a homogeneous medium，respectively，or periodically change the excitation threshold of cells. By monitoring the fraction of excitation cells，we find that there is a remarkable common feature for spiral wave meandering induced by different factors，i.e.，the fraction of excitation cells under spiral wave meandering is smaller than that under stable spiral wave，which indicates that the low excitability of a medium is related to the number of death cells and fatigue cells in the medium，and the periodical change of the excitation threshold of cells，respectively. The numerical results show that the decrease of the excitability of media always accompanies the decrease of the frequency of spiral wave. We hope the present work can provide help for medical workers on the prevention and treatment of heart disease.
2009, 58 (3): 1497-1503. doi: 10.7498/aps.58.1497
In this paper，we apply a nonlinear map model to investigate the influences of signal light and position of bus-stop on the traffic at a T junction. The dependence of point-based average flow of routes on bus-stop position，signal light cycle and split as well as vehicle swerve are numerically analyzed. Simulation results show that the interaction between bus-stop and signal light generates traffic clustering easily，and there exist relationships between signal light cycle，split，bus-stop position and the route flows.
Non-equilibrium molecular dynamics simulation for mechanism and drag reduction of underwater supercavitation in open system
2009, 58 (3): 1504-1509. doi: 10.7498/aps.58.1504
Non-equilibrium molecular dynamics was introduced for studying supercavitation mechanism and its drag reduction effect. Flow field details like local density distribution，local cavity number distribution，friction coefficient and gas volume percentage were calculated. The results showed that cavity number criterion is applicable in predicting supercavitation. Low cavity number area and actual cavity area are spatially separated. Velocity was the critical factor on cavity formation. Cavitator shape can affect gas volume percentage in cavity. Supercavitation can bring about 50%—90% skin friction reduction，comparing with cloud cavitation. The results agree with previous numerical simulation，showing the model is suitable for studying supercavitation mechanism in molecular scale and provides a valuable tool for investigating flow details.
2009, 58 (3): 1510-1516. doi: 10.7498/aps.58.1510
For a colloidal particle in a harmonic potential driven by a periodic signal，we study its thermodynamic behavior and obtain the exact expressions of the effective temperature and dissipated work by solving the corresponding Langevin equation. The results show that due to the cooperative effect of the potential，the signal and the noise，the energy of the environment can be transferred to the colloidal particle through the stirring action of the periodic driving force，which makes the effective temperature of the system increase greatly. Under the condition of dynamical resonance，the dissipated work also reaches its maximum.
2009, 58 (3): 1517-1525. doi: 10.7498/aps.58.1517
In order to determine the equation of state in the sospin asymmetrical nuclear matter，we have been engaged in find an experimental observable which sensitively shows the information of the nucleon-nucleon cross section and the symmetry potential in the intermediate energy heavy ion collision by using the isospin dependent quantum molecular dynamics in recent years. As a result, we have found several sensitive probes for extracting the information of the in-medium nucleon-nucleon cross section and the symmetry potential in the equation of state of the isospin asymmetrical nuclear matter. The mechanism of the above probes are investigated in detail. A brief summary and comments on the above results and the prospect of finding more probes in the future are presented.
2009, 58 (3): 1526-1530. doi: 10.7498/aps.58.1526
Using back-mask exposure technology，the hourglass-shaped X-ray compound refractive lens （XCRL） was made. Firstly，the theory of the refractive focusing of the hourglass-shaped XCRL was analyzed. Then the hourglass-shaped XCRL was manufactured using back-mask exposure technology for the first time，which avoids two-time masking and reduces the transfer times of the figure. The refractive focusing performance of the lens was tested with 10?keV monochromatic X-ray. The experimental results indicated that it has good focusing performance in one dimension, which is in general coincident with the calculated results.
ATOMIC AND MOLECULAR PHYSICS
Theoretical study on the structure，spectra and thermodynamic property of 2-（toluene-4-sulfonylamino）-benzoic
2009, 58 (3): 1531-1536. doi: 10.7498/aps.58.1531
The structure optimization and frequency calculation have been carried out at B3LYP/6-31++G** theoretical level，and IR spectrum，Raman spectrum and thermodynamic property at different temperatures have been obtained. The results indicate that the carbon and the oxygen in the —COOH group，and the nitron in —（OS）2—NH group come into formation of different large π bonds with the benzene rings，and there is a dihedral angle of 63.2° because of place blocking and conjugate effect. The first vertical excited state electronic transition energy was calculated by time-dependent density functional theory，and the maximal absorption wavelength was obtained at 312.7?nm，belonging to near UV，which is in good agreement with experimental value of 307?nm in dichloromethane solvent.
2009, 58 (3): 1537-1543. doi: 10.7498/aps.58.1537
Based on the potential energy function which considers the nuclear motion and isotopic effect of DTO (X1A1), the atomic and molecular reactive collision for O+DT has been studied by Monte-Carlo quasi-classical trajectory approach. It is shown that the reaction O+DT→DTO with a long-lived complex compound has no threshold energy at low collision energy, which agrees with the potential surface. When the collision energy is higher than 209.2 kJ·mol-1, the interchange reactions will start and then increase until DTO molecules are decomposed completely into D, T, O with the collision energy increasing. The interchange reactions O+DT(0, 0)→OD+T and O+DT (0, 0)→OT+D have corresponding threshold energies. The trajectories and collision section of interchange reactions show asymmetrical distribution which corresponds to the potential surface.
2009, 58 (3): 1544-1547. doi: 10.7498/aps.58.1544
The structure and dissociation energy of the ground state of ArH+ are calculated using QCISD（T）/ Aug-CC-pVTZ method. Based on the theory of atomic and molecular statics，the reasonable dissociation limit for the ground state （1Σ+） of ArH+ is derived. The potential energy curve and relevant optical constants of this state are obtained by least square fitting to the Murrell-Sorbie function. All calculation results are in good agreement with the experimental data.
A method to determine the orientations of adsorbed molecules by near edge structures and selection rules
2009, 58 (3): 1548-1555. doi: 10.7498/aps.58.1548
Since non-diffuse molecular orbitals （NMOs） are insensitive to environment，when molecules are adsorbed and not broken，the near edge structures involving NMOs will still resemble structures of corresponding free molecules. If we probe adsorbed molecules with polarized X-ray photons，relative intensities of photoabsorption spectra near molecular edges will be different for various geometric arrangement of X-ray polarization. Such features can be used to determine orientations of adsorbed molecules.
The influences of the finite nuclear size effects on the energy levels and wavefunctions of hydrogen-like ions
2009, 58 (3): 1556-1562. doi: 10.7498/aps.58.1556
Based on the relativistic theory, the wavefunctions and low-lying levels of highly charged states of hydrogen-like ions for the shells n=1—3 were calculated using different nuclear models——point-like nuclear and Fermi nuclear models with two parameters, respectively. The influence of the finite nuclear size on wavefunctions and level energies were analysed. Furthermore, a fitting formula related to nuclear parameter a and c in Fermi nuclear model for finite nuclear effects on the atomic level energy is deduced. The mutual influence between the relativistic effect and the finite nuclear size effects were discussed. It is found that there is a strong coupling between relativistic effect and finite nuclear size effects for high-Z elements.
2009, 58 (3): 1563-1568. doi: 10.7498/aps.58.1563
We propose a novel controllable electrostatic double-well trap scheme by using two charged ring wires and two parallel transparent electrodes. The spatial distributions of the electrostatic field from the above charged wires and the charged plates are calculated. We also analyze the advantages of the proposed scheme, and discuss the loading process of cold molecules from a cold molecular beam into our trap. Our study shows that our controllable double-well trap is not only convenient to trap, manipulate and control cold polar molecules in the weak-field-seeking states, but also has the potential applications in molecule optics field，such as molecular interference, molecular entanglement, and molecular collisions, even to study the molecular BEC in the double-well trap, and so on.
2009, 58 (3): 1569-1573. doi: 10.7498/aps.58.1569
In this paper, the theory of atomic cooling in an integrating sphere is studied. During designing an integrating sphere system, the effects of the parameters of the sphere on the cooling, including the reflectivity of the material, the shape of the sphere and holes in the sphere have been considered carefully. The experiment of 87Rb atomic cooling in an integrating sphere was performed. The experimental results show that the atoms in the integrating sphere are cooled down evidently. And the relation between the detuning of the cooling laser and the absorption signal of cold atoms was measured.
2009, 58 (3): 1574-1578. doi: 10.7498/aps.58.1574
By numerically solving time-dependent Schrdinger equation, we obtain high-order harmonic generation （HHG） spectra from the one-dimensional H atom model submitted to linear polarization bichromatic field. It is found that, appropriate bichromatic field could be a source of attosecond pulse generation since it produces a ligher line-density in harmonic generation spectra （HGS）. Based on it, we analyze the mechanism of generating denser HHG spectral lines in detail, and give density-selection numerical experiential formulas for different pulses duration, to achieve further control of the line density of HGS.
2009, 58 (3): 1579-1585. doi: 10.7498/aps.58.1579
By solving the time-dependent Schrdinger equation with split-operator method, we study the high harmonics of one-dimensional helium atom exposed to the two-color laser field composed of IR field and UV field, and analyze the characteristics of the attosecond pulse produced by the high-order harmonics. It is found that the width of the attosencond pulse is shortened by the increasing intensity of IR field in the combined laser field. By adjusting the time delay between two lasers, we can enhance the contribution of one of the electron trajectories and suppress that of the other. Thus we can obtain an isolated sub-100 as pulse.
Digital signals （square wave） are superpositions of many frequency components in frequency domain. We analyze and calculate the coupling potentials between the atom and the frequency components respectively, and demonstrate that the atomic trapping adiabatic potential can be generated by taking into account the total coupling potential. An application scheme of the digital signal in an atom chip is proposed.
2009, 58 (3): 1590-1594. doi: 10.7498/aps.58.1590
We have measured the change of fluorescence from cold 87Rb atoms after magnetic field of the magneto-optic trap is turn off. A rise in fluorescence within several tens of milliseconds was observed. Analyzing this phenomenon in connection with the experimental conditions, we found that incoherent pumping field due to radiation trapping in the high density cold-atom cloud was the reason of fluorescence weakening under tight confinement by the magneto-optic trap. We have also performed a simple numerical simulation, which indicated that the calculations agree with experimental results only when the effect of frequency redistribution of scattered light is taken into account.
2009, 58 (3): 1595-1602. doi: 10.7498/aps.58.1595
A Plasma Needle using a dielectric barrier discharge reactor at atmospheric pressure with a funnel-shaped nozzle was designed and realized. The preliminary characteristics of the plume and applications in the sterilization of Streptococcus mutans （S.mutans）, which is the most important microorganism causing dental caries, were presented in this paper. The reactor produced a cold plasma plume with temperature not higher than 315?K at 28?W. The effect of oxygen, which was injected downstream in the plasma afterglow region through a steel tube, was studied using its spectrum. The results show that addition of 26 mL·min-1 O2 led to the transport of atomic O further without significant effects on the jet length. The experiments show the best parameters are 15?W power, 01?m3·h-1 He with 25% O2 addition and separation of needle-to-sample 12?mm. It is found that ultraviolet rays, O，OH and He radicals can reach and act with S.mutans. To find critical radicals which are related to sterilization, we compareed the probe spectrum at atmosphereic pressure with that in agar.
2009, 58 (3): 1603-1607. doi: 10.7498/aps.58.1603
The averaged binding energy, energy gap, atomic charge and total charge density of the MgO nanotube clusters were calculated with B3LYP method at 6-31G（d） level. The calculations show that the everaged binding energy decreases approximately linearly with increasing coordination. The structural stability increases in company with length of MgO nanotube clusters, and the most stable structure is 3MR species. The charge transfer increases with length of MgO nanotube clusters, the averaged atomic charges of 2, 3 and 3 converge to 1298, 1270, 1306, respectively. Mixed covalent and ionic bonding property always exist in MgO nanoclusters.
CLASSICAL AREA OF PHENOMENOLOGY
An efficient algorithm of the electromagnetic dyadic Green’s function in a horizontal-layered anisotropic medium
2009, 58 (3): 1608-1618. doi: 10.7498/aps.58.1608
In this paper, we advance an efficient algorithm of electromagnetic spatial dyadic Greens function in a horizontal-layered anisotropic medium through high order window function and so on. First, we use the high order window function to transform the Sommerfeld integrals of dyadic Greens function into integrals along a generalized steep descent path. And we give a new and higher order of power series of expansion expression of Hankel transforms of the window function and an accurate formula of Lommel function so that the dyadic Greens function can be precisely computed either near or far from the transmitter. Then, we divide the integral path into a series of subintervals based on the zeros of Bessel function and compute integral per subinterval using an improved adaptive Gauss quadrature. Furthermore, an algorithm of the finite continued fraction expansion is used to sum up the integrals on each subinterval to greatly accelerate the convergence velocity of the numerical integration along the descent path. Finally, our numerical results validated the efficiency of the algorithm.
Derivation of the material parameters for regular N-sided polygonal cylindrical cloak and the invisibility verification
2009, 58 (3): 1619-1626. doi: 10.7498/aps.58.1619
General expressions of constitutive tensors of the N-sided regular polygonal cylindrical cloaks are derived based on the coordinate transformation theory, then there are some full-wave simulations of the cloaks.The results of full-wave simulations validate the general expressions of constitutive tensors we derived. Furthermore, factors that degrade the cloaks invisibility are analyzed.
Investigation on the characteristics of electromagnetic scattering from 2-D fBm rough surface of layered medium
2009, 58 (3): 1627-1634. doi: 10.7498/aps.58.1627
The electromagnetic scattering from the rough surface of layered medium with plane wave incidence is investigated. A 2-D fBm fractal rough surface is used to simulate the natural rough surface of layered medium, and the formulae of the scattering coefficient of the 2-D fBm fractal dielectric rough surface of layered medium with the plane wave incidence is derived by using the small perturbation method in association with the power spectrum density of 2-D fBm fractal rough surface. The angular distribution of the bistatic-scattering coefficient of HH polarization are obtained by numerical computation, the influence of fractal dimension, the permittivity of substrate medium, the permittivity and the mean layer thickness of intermediate medium, the surface roughness parameters and the frequency of the incident wave on the bistatic-scattering coefficient is discussed. The fractal characteristics, the basic characteristics, the zonal characteristics and the characteristics with varying frequency of the scattering coefficient from 2-D fBm fractal rough surface are obtained.
2009, 58 (3): 1635-1641. doi: 10.7498/aps.58.1635
Radiography using ultra-short laser-produced proton beams is a development of traditional proton radiography. According to the characteristic of laser-produced proton beam, using FLUKA Monte-Carlo program, the quantitative simulation of proton radiography is studied. From the simulation of three typical cases （half-plane target and ladder target, hohlraum with a plastic ball in it,and detection of magnetic field with mesh method）, the main physical factors that effect the proton radiography are discussed. The advantage of radiography of laser-produced protons, such as high sensitivity to boundary, high spatial resolution, and high sensitivity to magnetic field, is demonstrated.
2009, 58 (3): 1642-1647. doi: 10.7498/aps.58.1642
The beam splitting and polarizing principle of modified Wollaston prism are presented. This paper analyses the propagation track of light wave in modified Wollaston prism by wave-normal-tracing method at random incidence angle and the formula of the path difference between e and o light waves are deduced. Computer simulations are carried out to give the curve of the optical path difference varying with incidence angle, incident azimuth angle, structural angle and wave length. The results will provide a theoretical basis for the study of polarization prisms and the development of polarization splitting apparatus.
The influence on the radiation characteristics of an amorphous nanocluster by introducing photonic crystals
2009, 58 (3): 1648-1654. doi: 10.7498/aps.58.1648
The amorphous nanoclusters have short range order and long range disorder structures ordinarily. The radiation spectrum characteristics of an amorphous ZnO nanocluster are studied by using finite difference time domain method and the radiation spectrum shows as spontaneous emission. To control the spontaneous emission, photonic crystal is introduced to lead the radiation emission to the needed frequency. An easier and cheaper manufacture method is put forward in which the nanocluster should be inserted between two colloidal crystal films which self-assembled by uniform colloidal nanoparticles. According to this idea, a two dimensional system is constructed and the radiation characteristics of this system are simulated. The results show that the energy is controlled in this system effectively. This scheme can provide a new way to manufacture low threshold micro-lasers feasible for imbedding in optical integrated circuits.
Propagation and spatiotemporal coupling of iso-diffraction ultra-short pulsed Hermite Gaussian beams in free space
2009, 58 (3): 1655-1661. doi: 10.7498/aps.58.1655
A family of solutions called iso-diffraction ultra-short pulsed Hermite Gaussian beams （UPHGB） are obtained based on the paraxial propagation equation. The propagation of UPHGB is investigated in detail. The examples shows that: the nonuniformlly distributed group velocity causes the time delay at the beam periphery, which in turn induces the deviation of the transverse distribution from the Hermite Gaussian function. In propagation, the number of pulse polarity inverions varies with the order of the UPHGB. And this phenomenon originates in the difference between the group velocity and the phase velocity in UPHGB.
2009, 58 (3): 1662-1667. doi: 10.7498/aps.58.1662
In this paper, a new method of encrypting a color image in one channel based on double-phase encoding is presented. In this method, the colors of a color image are converted from RGB to HSI, so the I component can be used as the original image which could be encoded with double-phase. The kinoform of S is obtained by using double-random phase encryption and the H component can be used as the two phases. It is difficult to recover the S component if the phase keys are not available, because double-random phase encoding is robust to blind retrieval trials, so the security of the method proposed is guaranteed. Computer simulations are presented to illustrate the efficiency of this method.
2009, 58 (3): 1668-1674. doi: 10.7498/aps.58.1668
A wavefront reconstruction technique by two-step generalized phase-shifting interferometry （GPSI） is proposed and verified by optical experiments. According to the statistical characters of the diffractive field, a blind extraction algorithm is developed, by which the unknown phase shift value in interferometry can be successfully extracted. The proposed method can retrieve the real amplitude of object wave field by using two interferograms, the recorded object and reference wave intensities, and an extracted phase shift, without the assistance of additional Fourier spectrum analysis or digital filtering. In optical experiments, the feasibility of this method for both the indirect object （digital images cast on a spatial light modulator, SLM） and the direct three-dimensional diffused object inputs has been discussed and investigated in detail, and the experimental results have convincingly verified the usefulness and effectiveness of this scheme in practice.
Fabrication of LaF3: Er, Yb nanoparticle doped organic-inorganic hydrid material waveguide amplifier and its properties
2009, 58 (3): 1675-1678. doi: 10.7498/aps.58.1675
LaF3: Er, Yb nanoparticles doped organic-inorganic hydrid material waveguide amplifier is fabricated. The optical gain and upconversion in the waveguide are studied. The upconversion emission bands at 405,520,544 and 650?nm are assigned to 2H9/2→4I15/2，2H11/2→4I15/2，4S3/2→4I15/2 and 4F9/2→4I15/2 transitions, respectively. The possible upconversion mechanism of Er3+ in this material was analyzed. A 155 dB/cm relative gain was observed when pumped by a 976?nm laser at 160 mW power.
2009, 58 (3): 1679-1684. doi: 10.7498/aps.58.1679
Here we propose a scheme for enhancing the nonlocality of three-mode Gaussian state light fields. It is found that three-mode Gaussian State can become non-Gaussian by the non-Gaussian operation of an IPS process, It is vertified that nonlocality of Gaussian state can be enhanced by Bell inquality.
2009, 58 (3): 1685-1688. doi: 10.7498/aps.58.1685
The cavity field spectra of two-mode field both in the binomial state interacting with a two-level atom through intensity-dependent coupling in an ideal cavity is investigated. The results for the weak initial fields are calculated. The influence of the quantum interference on the cavity field spectra is discussed. Its found that when the difference of the initial two-mode field frequency Δ is larger than g （g is the coupling coefficient between atom and the field） the influence of the quantum interference on the spectra structure can be ignored, the system spectrum is only the superimposition of the two mode spectra. When Δ is smaller than g the quantum interference between the two-mode spectra is especially obvious. The quantum interference between the two-mode spectra should not be considered when the initial field is stronger.
2009, 58 (3): 1689-1693. doi: 10.7498/aps.58.1689
Study of LD pumped single longitudinal mode Cr,Tm,Ho∶YAG microchip laser pumped by a 785?nm laser diode（LD） is reported. The pump threshold power of the Cr,Tm,Ho∶YAG microchip laser was 1060?mW and the maximum single longitudinal mode output power was 31?mW. The output power against the laser crystal temperature demonstrated the temperature sensitivity of Cr,Tm,Ho∶YAG crystal. The frequency tuning property of the Cr,Tm,Ho∶YAG microchip laser was also measured by changing the temperature of the crystal, and a tuning coefficient of 14?GHz/℃ was obtained.
Study on the effects of carrier transport and parasitic parameters on the modulation response of tunnel regenerated vertical-cavity surface-emitting lasers with double active regions
2009, 58 (3): 1694-1699. doi: 10.7498/aps.58.1694
A rate equation model of multi-quantum wells and multi-active regions were presented. The effects of photon density and the carrier capture-escape-tunnel time on the frequency response of single active region vertical-cavity surface-emitting Laser （VCSEL） and tunnel-regenerated VCSEL with two active regions were simulated by the small signal analysis. The result of simulation shows that the modulate bandwidth of tunnel-regenerated VCSEL with two active regions is larger than that with single active region under the same drive current, then its causes are discussed. Moreover, we simulate the frequency response of the parasitic circuit of tunnel-regenerated internal-contact oxide-confined VCSEL with two active regions after analyzing its parasitic parameters.
2009, 58 (3): 1700-1708. doi: 10.7498/aps.58.1700
In pulsed diode laser side-pumped solid-state laser, time-varying distribution of temperature in laser crystal is numerically calculated. Three-direction pumped beam intensity distribution in laser crystal is analyzed. Based on the solution, the temperature distribution and its influence in single-pulse process of pulsed diode laser array side-pumped Nd∶YAG laser is obtained by finite element method. The results show that the process of temperature rise is influenced by pump condition and cooling method, but the main influencing factor are the pump conditions such as pumping power and beam waist. Cooling process is influenced by crystal thermo-physical parameters, radius and cooling condition. After the transient temperature distribution has reached dynamic equilibrium, because of radius temperature gradient periodically changing with time, the optical path difference between center and edge beam is also periodically changing with time.
Generation of femtoseond Ti:sapphire laser at 10MHz repetition rate by extending laser cavity with a telescope
2009, 58 (3): 1709-1714. doi: 10.7498/aps.58.1709
We demonstrated a femtosecond Ti:sapphire oscillator at 10?MHz repetition rate by introducing a specially designed multi-pass telescope to increase the cavity length. Stable mode locking laser with average power of 200 mW is obtained under 532?nm laser pump of 5?W power, corresponding to a single pulse energy of 20?nJ. Based on this laser, we further explored the characteristics of pulse duration and spectrum with the net intracavity group-delay dispersion （GDD）. The result indicates that the near-bandwidth-limited pulse can be obtained when a little net negative GDD exists, the optimized pulse duration as short as 56?fs was generated in this case. The positive GDD will lead to a widened pulse with the increase of positive GDD, and the pulse duration can extend to more than 600?fs with the largest allowable positive GDD.
2009, 58 (3): 1715-1718. doi: 10.7498/aps.58.1715
A high power intracavity optical parametric oscillator （OPO） with a type Ⅱ KTiOPO4（KTP） is reported. The OPO is placed in a high power, linearly polarized diode-side-pumped Nd∶YAG laser cavity. By a suitable design of the OPO cavity, a maximum of 295 W at 2?μm is reached with repetition rate of 5?kHz. The output power characteristic of OPO is investigated. The fluctuation of OPO output power in less than 1.4%.
2009, 58 (3): 1719-1725. doi: 10.7498/aps.58.1719
Here we present a theory which predicts the process of ultraviolet generation by frequency doubling of focused green Gaussian beam in BBO crystal. In this theory, phase matching acceptance angle, walk-off angle and the divergence of fundamental beam have been considered. Numerically computed results show that the variations of the waist of Gaussian beam can lead to changes in conversion efficiency and in the ultraviolet transverse intensity distribution of far-field. Comparison between the numerical simulation and experimental results supported our theoretical analysis.
2009, 58 (3): 1726-1730. doi: 10.7498/aps.58.1726
The theoretical model of magneto-optic fiber Bragg gratings （MFBG） is proposed and the nonlinear coupled-mode equations for circularly polarized light in MFBG is derived for the first time. Our analysis shows that the coupling between right- and left-handed circularly polarized light along with the magnetically circular birefringence （the Faraday effect） resulting from the nonlinear effects and the grating structure is responsible for the coupling of forward and backward guided optical waves with identical states of polarization. In the MFBGs, the reversal of transmission characteristics and lower power threshold of nonlinear bistable switching can be achieved under appropriate magneto-optic bias. The MFBG-based pulse reshaping scheme by utilizing cross-phase modulation （XPM） of right- and left-handed circularly polarized light has a great advantage in magnetic adjustability over that based on conventional fiber gratings and is useful for the development of dynamically controllable all-optical 3R regenerators.
Theoretical analysis of novel Brillouin scattering properties in photonic crystal fibers based on silica rod model
2009, 58 (3): 1731-1737. doi: 10.7498/aps.58.1731
Based on an approximate model for acoustic waves in a silica rod with circular cross section, we theoretically investigated the dispersion properties of the hybrid acoustical modes and the acousto-optical interactions in the small core photonic crystal fiber. The calculation result shows that the dual-peaked Brillouin scattering gain coefficient spectrum is caused by the mode coupling of the hybrid acoustical modes in the small fiber core. Together with the dispersion properties of the acoustical modes, the influence of the pump wavelength and temperature on the dual-peaked Brillouin scattering gain coefficient spectrum are also calculated via their influences on the acoustic wave vector and material parameters. Our theoretical results agree with the experimental results well. And we also discuss the limit of application of this model through comparing the theoretical and experimental results.
2009, 58 (3): 1738-1744. doi: 10.7498/aps.58.1738
The experimental investigation of the nonlinear hot image effect in brand-band pulsed laser beams is reported, placing emphasis on the observation of the formation of hot images and the influence of incident average power of pulse, pulse width, and thickness of the nonlinear medium on the location and intensity of hot images. It is shown that, hot images can be formed from obscurations in the broadband laser beam through a nonlinear Kerr medium slab, as in the case of the monochromatic continious light beam, and are located in the plane symmetrical to the obscuration with respect to the nonlinear slab. In addition, with the incident average power of pulse increasing, the intensity of hot image increases and ultimately reaches saturation, while with the pulse width increasing, the intensity of hot image decreases for a pulse of given energy. On the contrary, it increases for a pulse of given peak power.
Investigation of the operation characteristics of terahertz-wave parametric oscillator based on LiTaO3
2009, 58 (3): 1745-1751. doi: 10.7498/aps.58.1745
Based on the basic principle of the stimulated polariton scattering process, the operation characteristics of terahertz-wave parametric oscillators （TPOs） using the LiTaO3 （LT） crystal, including the ability of frequency-tuning, THz gain and absorption coefficient and the output directivity of THz wave through the arrayed Si-prism coupler, is theoretically discussed in detail. It is found that the excellent performance of LT-TPO can be achieved through the employment of the short-wavelength pump, the high pump energy and short cavity for TPO, based on the characteristics of the A1-symmetry polariton mode and the outstanding nonlinear optical properties of LiTaO3, which is then proved to be a promising candidate material for TPO. The research results provide a useful guide for the future practical operation of LT-TPO.
2009, 58 (3): 1752-1757. doi: 10.7498/aps.58.1752
In strongly nonlocal nonlinear media, the evolution of the optical beam is governed by Snyder-Mitchell model. By applying the variational method, we obtain an approximate analytical solution of Snyder-Mitchell model, i.e., the rotating azimuthon, which has an inherent rotation. Under certain conditions, the rotating azimuthon can be reduced to the radially symmetric optical vortex soliton.
2009, 58 (3): 1758-1764. doi: 10.7498/aps.58.1758
We studied new left-handed material composed of hexagonal split resonant rings （SRRs） based on trigonal resonators and metal wires through simulation and experiment. Simulated negative permeability material based on periodic structures of trigonal SRRs, in contrast to simulation result based on closed split resonant rings （CSRRs）, we found that the trigonal SRRs can generate negative permeability, and multilayer SRR simulation shows the coupling can enhance the resonant frequency and broaden resonant frequency band. We designed a new kind of left-handed material combined with hexagonal resonator based on trigonal resonators and copper wires. Simulation shows that the structures have good left-handed property. We have fabricated experimental samples which show negative refraction when the frequency lies in 93—108 GHz rangc. This has important significance on design and study of new types of periodic structures of left-handed materials.
Anomalous phenomena of electromagnetic wave propagation in metamaterials for arbitrary orientation of optical axis
2009, 58 (3): 1765-1772. doi: 10.7498/aps.58.1765
When there is an angle between the anisotropic metamaterials' optical axis and the electromagneticwave propagation axis, anomalous omnidirectional total reflection and anomalous negative refraction are discovered at the interface. The functional relation between incident angle and refractive angle of energy flow is obtained. According to this relation, we can restructure the refractive angle as negative or positive readily by selecting suitable permittivity and permeability tensors. And under these conditions, an anomalous transmittance emerges，such that when incident angle is less than a value, especially in the vicinity of vertical incident, the transmittance is minimum or even zero. According to these characteristics, a new slab spatial filter is put forward. Compared with the traditional space filter system, this new spatial filter's volume is smaller. And these characteristics can also be used to build a reflector of low spatial frequency.
2009, 58 (3): 1773-1778. doi: 10.7498/aps.58.1773
A full-field optical coherence tomography system using an achromatic phase shifter based on a rotating half-wave plate to implement phase shifting is developed. The phase shifter can achromatically introduce phase shift of eight times the rotating angle of the half-wave plate, and can rapidly provide various phase shifts for various algorithms. Real phase shift is measured and the result demonstrates that the system gives a phase shift of eight times the rotating angle of the half-wave plate, showing the achromatic phase shifter model is correct. Imaging experiment results of a mirror using Hariharan algorithm show that the system has high phase shift precision. A coin as the sample is imaged to demonstrate the performance of the system.
2009, 58 (3): 1779-1784. doi: 10.7498/aps.58.1779
Single-photon-counting imaging technology has been widely used in ultraweak bioluminescence, space environment detection and nuclear radiation detection. The structure and working principle of an ultraviolet single photon imaging system based on the microchannel plates and the wedge and strip anode are introduced. The gain characteristic of dark count of two and three microchannel plates is investigated under different voltages respectively. The experimental and fitted results show that the dark count pulse height distribution of microchannel plate has exponential distribution, and the dark count rate rises as the voltage increases. It is shown that the gain becomes more homogeneous as the voltage increases by measuring the pulse height distribution under different voltages. Then the effects of microchannel plate voltage and distance on system resolution with two microchannel plates are tested. It is revealed that the system resolution rises as the voltage of microchannel plate increases, and can be improved also by increasing the distance of microchannel plate properly.
Ultrahigh-speed all-optical encoder based on four-wave mixing in semiconductor optical amplifiers with PolSK modulated signals
2009, 58 (3): 1785-1792. doi: 10.7498/aps.58.1785
A novel scheme for ultrahigh-speed all-optical encoder based on four-wave mixing （FWM） in semiconductor optical amplifiers （SOAs） with PolSK modulated signals is proposed. Considering the polarization dependency of SOA, a comprehensive polarization-dependent broad-band dynamic model is presented. By numerical simulation, this kind of all-optical encoder is theoretically realized, and the effects of two input signal powers, injected current, and polarization dependency of SOA on the output performance of the encoder are analyzed.
2009, 58 (3): 1793-1797. doi: 10.7498/aps.58.1793
The characteristics of co-doping Al3+ in ytterbium-doped silica-based fiber used for high-power cladding pumped laser were analyzed based on experimental analysis. The results show that the optimum mole percent of Al3+ to Yb3+ is 9—11 for high concentration of ytterbium-doped silica-based fiber at which low concentration quenching probability, high absorption coefficient and proper numerical aperture can be obtained. Meanwhile, ytterbium-doped silica-based fiber preforms were fabricated by MCVD and special solution doping technique. By soot layer temperature experiment and test of the related parameters of the drawn fiber, the results show that the optimum temperature for making soot layer can be accurately controlled and the absorption coefficient at 976 nm was as high as 620 dB/m with good repeatability. This conclusion makes a useful reference for fabrication of ytterbium-doped Al3+ co-doped fiber.
2009, 58 (3): 1798-1805. doi: 10.7498/aps.58.1798
It is important for underwater acoustic modeling and passive localization to estimate the geoacoustic properties with high accuracy. A geoacoustic inversion scheme was presented, which uses a broadband source to generate the linear frequency-modulated signal at different ranges and depth. The signal was received by a vertical array. The bottom reflection loss was extracted by matched filtering and then used to estimate the sea-bottom density and sound speed. Meanwhile, an inversion method based on sub-bottom reflection was investigated using the experimental data. Because the direct arrivals in the water were influenced strongly by the internal waves, the first sea-bottom reflection was taken as the reference path to calculate the relative arrival time and amplitude of sub-bottom reflections. Firstly the sediment sound speed and thickness were estimated using different source depth and receiver depth. Then the sediment attenuation was estimated by assuming that it has linear frequency dependence. The estimated values of the sediment properties compared well with the core data, chirp sonar data, and the matched field inversion results.
2009, 58 (3): 1806-1811. doi: 10.7498/aps.58.1806
The thermal interface resistance of the helix slow-wave structure （SWS） has been studied theoretically and experimentally. The effect of the thermal resistance at two interfaces on heat dissipation capability of the SWS is analyzed. A novel method to calculate the thermal interface resistance has been developed, and its accuracy and feasibility were validated by experiments. With this method, the thermal interface resistances at two interfaces can be calculated separately, considering the variation of the material performance with the temperature changes. This novel method is used to study the effect of the rod material and the assembling method on the thermal interface resistance.
2009, 58 (3): 1812-1818. doi: 10.7498/aps.58.1812
The segregation of the binary granular mixture in Brazil nut problem was simulated by using discrete element model. The influences of the frequency and the amplitude of the vibration on the segregation are discussed. The simulation results show that the segregation between big and small particles can be predicted accurately. When the frequency or the amplitude of the vibration is low, the final segregation efficiency is low, but the segregation is quite stable. When the frequency or the amplitude of the vibration is high, the final segregation efficiency is still low, but the segregation is unstable. An optimum operating point with a moderate frequency and a moderate amplitude of the vibration exists in the process of segregation in Brazil nut problem.
2009, 58 (3): 1819-1825. doi: 10.7498/aps.58.1819
The formation of three-dimensional sandpile was simulated by using discrete element model. The influence of sliding friction and rolling friction of particles on the formation of sandpile was discussed. The simulation results show that the angle of repose of sandpile is determined by both sliding friction and rolling friction. The trec-shaped microscopic mechanical structure in the sandpile was revealed by the simulation. The stress distribution at the bottom of sandpile was also obtained by the simulation. The simulation results show that when the angle of repose of sandpile is large, normal stress profiles with a clear stress dip near the center of the pile is generally formed, and when the angle of repose of sandpile is small, the maximal normal stress generally appears near the center of the pile. Which type of the stress distribution at the bottom of sandpile will emerge is rather accidental,depending on the real process of pileing.
2009, 58 (3): 1826-1832. doi: 10.7498/aps.58.1826
Many insects and some animals, such as and crickets, tree frogs, can utilize a thin film of confined liquid between the pad and the smooth surface to facilitate climbing vertical walls and even walking on the ceiling. Our previous experiments based on a ball-disk microtribometer have revealed that a sudden unstable spreading or shrinking of the confined liquid film occurs when the volume reaches a critical value, which respectively corresponds to an unstable increasing or decreasing of interfacial adhesive force. This unstable behavior of the confined liquid film has important implications on the adhesion/releasing mechanism of wet bio-adhesive pad to or from the smooth surface. In this article, we highlight some of the switching mechanisms for capillary adhesion through theoritcal analysis and further experiments. It is found that, the unstable spreading and shrinking of confined liquid film is connected with the instability of the cantilever stiffness, and the maximum interfacial adhesive force decreases with the liquid volume and strongly depends on the film thickness of the central area. Inspired by these results, strategies for a bio-adhesive pad to realize `switchable' adhesive mechanism is analyzed, which will shed light on the design and control of a biomimetic adhesive pad.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2009, 58 (3): 1833-1837. doi: 10.7498/aps.58.1833
The saturation of stimulated Raman scattering （SRS） through Langmuir decay instability （LDI） and electron trapping in laser-plasma interaction process is studied. Analytical expressions for the saturation time of SRS are obtained for both the LDI and electron trapping schemes in 1-D homogeneous plasma irradiated by unrelativistic laser beams. The simple analytical model agrees well with numerical simulation and experiment in respect of the dependence of the saturation time of SRS on the parameters of lasers and plasmas.
2009, 58 (3): 1838-1843. doi: 10.7498/aps.58.1838
A novel magnetically tunable liquid crystal terahertz switch is designed to reduce the coupling loss. The main structure of the switch is the hollow-core Bragg fiber with its cladding constructed by periodically setting of high density polyethylene and nematic liquid crystal E7 The refractive index of the E7 can be changed by the application of outside magnetic field and thus alter the loss property of the Bragg fiber dramatically to achieve its function as a switch. The main advantage of this switch is that it can eliminate the loss of coupling with fibers,and what is more,this switch can select the basic mode and is easy to be controlled. This article uses the finite element method to obtain the parameter of the switch and the simulated value of the extinction ratio reaches 2634 dB.
2009, 58 (3): 1844-1848. doi: 10.7498/aps.58.1844
The effect of oscillating sheath on the near-wall conductivity is studied by using two-dimensional particle-in-cell （PIC） method. The results show that when the secondary electron emission （SEE） coefficient is greater than 1, the sheath is in the state of oscillation, in which the electron-wall collision flux periodically oscillates along the direction parallel to the wall, and the order of oscillating wavelength is the same as that of the electrostatic wavelength. The order of electron-wall collision frequency is 1—2 orders higher than the frequency of the classic shell state, and the contribution of collision frequency to the current in the channel cannot be neglected. Though the oscillating shell increases electron-wall collision frequency compared to classic shell, it prevents electron-wall collision at the same time.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Molecular dynamical investigation on plastic behavior of Cu(100) twist-grain boundary under uniaxial tension
2009, 58 (3): 1849-1856. doi: 10.7498/aps.58.1849
Misfit dislocation structures at twist-grain boundary and its effect on grain boundary strength are investigated by using molecular dynamics simulation with EAM potential. The results reveal that the density of misfit dislocations which are formed on small angle twist-grain boundary is increased as the twist angle increased. Dislocations nucleate at each unit of the dislocation networks and the yield stress is increased as the density of misfit dislocations increases since grain boundary is strengthened by the interaction between dislocation networks. Face defect is formed at large angle twist-grain boundary, and the dislocations nucleate at the atomically sharp corner of the grain boundary. The yield stress is kept almost at the same value since there is little effect on the nucleation force of dislocation on face-defect grain boundary.
Fabrication of InP nano inner cladding fiber and its amplification propertg based on quantum size effect
2009, 58 (3): 1857-1862. doi: 10.7498/aps.58.1857
We uses improved chemical vapour deposition and drew fibres with InP nano thin films. Based on the hydrogen atom model, we calculate the corresponding size of the InP particle aB=8313 nm. By the quantum size-effect, we calculate the change of the energy band of particles with different sizes and the corresponding light absorption wavelength. From the system testing, the fibres have gain at 906—1044 nm, 1080—1491 nm and 1524—1596 nm. The results showed that the energy level of inner cladding materials creates a red shift when the thickness of thin-film is 5—50 nm. The fibre creates optical amplification.
2009, 58 (3): 1863-1869. doi: 10.7498/aps.58.1863
The generalized gradient approximation （GGA） based on density functional theory（DFT）is used to analyze the geometric and electronic properties of the endohedral fullerene MC20F20 （M=Li, Na, Be, and Mg）. The analysis of geometric structure indicates that the C—C bond length increases with the atomic number M, while the C—F bond length hardly changes. The doping energy of all kinds of MC20F20 is negative, indicating that the encapsulation would proceed under certain conditions. The electronic structure demonstrates that MC20F20 （M=Li and Na） and MC20F20 （M=Be and Mg） have different energy gaps and magnetic moments. The energy gaps of MC20F20 （M=Li and Na） are very small, while the energy gaps of MC20F20 （M=Be and Mg） are larger than that of C60 On the other hand, the MC20F20 （M=Li and Na） have 1μB magnetic moment, whereas the magnetic moments of MC20F20 （M=Be and Mg） are zero.
Comparison of the compositions and structures of electrodeposited Cu-poor and Cu-rich Cu(In1-xGax)Se2 films before and after selenization
2009, 58 (3): 1870-1878. doi: 10.7498/aps.58.1870
Cu-poor and Cu-rich near stoichiometric Cu (In1-x Gax)Se2(CIGS) precursor films were obtained by one-step electrodeposition from acid aqueous baths, and the compositions and structures of the as-deposited films before and after selenization were investigated. The straightforward experimental evidence was first obtained, which showed that Cux Se compound was conglomerated as rather large crystal grains which was distributed on the surface of the film for the Cu-rich films after seleniztion. The results indicated that the film composition was changed barely after selenization. When the ratio Cu/(In+Ga)＜1.1, there were many cracks on the surface of CIGS after selenization. When Cu/(In+Ga)＞1.2, no cracks were formed on the surface of the thin films. The efficiency of solar cells bnilt directly from Cu-poor films after selenization achieved above 2%, which is pending further investigation. Furthermore, the efficiency of solar cells bult from Cu-rich CIGS films after selenization and deposition of a few In, Ga and Se by PVD has achieved 6.8%.
2009, 58 (3): 1879-1884. doi: 10.7498/aps.58.1879
Based on the Gray equation of state，the Grüneisen models of ργ=constant，Gray，GRIZZLY and the Grüneisen parameter calculated from ab initio were used to calculate the melt line, isentropic compression, isotherm compression and isentropic release lines of aluminum. Comparing the calculated lines with the experimental data,the GRIZZLY Grüneisen model was found to be the best model for the equation of state of aluminum in the pressure range of about 500 GPa. The ργ=constant model is not as good as the GRIZZLY model. The Gray model and the Grüneisen parameter calculated ab initio fits the experimental data at high pressure badly.
2009, 58 (3): 1885-1889. doi: 10.7498/aps.58.1885
Well-aligned ZnO nanorod array films (ZnO-NAFs) were coatedon common glass substrate by two-step method. A thin buffer layer of ZnO seeds were first deposited via RF magnetron sputtering,the ZnO-NAFS were then grown in a simple aqueous solution. We report a surface-modification induced hydrophilicity to superhydrophobicity transiton on ZnO-NAFs. The sample was characterized by scanning electron microscopy (SEM). The surfaces of ZnO-NAFs was superhydrophobic with a three-phase contact angle of 151°±0.5°, while the sliding angle is 7°. The superhydrophobicity of ZnO-NAFs was validated by Cassie's model.
2009, 58 (3): 1890-1895. doi: 10.7498/aps.58.1890
The adsorption of hydrogen in AFS and AST molecular sieves are studied using grand canonical Monte Carlo （GCMC） technique in this paper. Dubinin-Astakhov（DA）method was employed to analyzed the physical reasons which affect the storage of hydrogen. The work in this paper facilitates direct rational design and synthesis of the materials which apply to storage of hydrogen, and provide a powerful theoretical support to improve the hydrogen storage capability of the materials.
2009, 58 (3): 1896-1900. doi: 10.7498/aps.58.1896
We report an experimental and theoretical study of maximum modal gain of p-doped 13 μm InAs/GaAs quantum dot （QD） lasers. The maximum modal gain of the QD laser with five stacks of QDs is as high as 175 cm-1, which is the same as that of the undoped laser with identical structures. The expression of the maximum modal gain is derived and it is indicated that p-doping has no effect to the maximum modal gain.We theoretically calculated the maximum modal gain of the QD lasers and the result is in a good agreement with the experimental data. Furthermore, QDs with lower height or smaller aspect ratio are beneficial to achieving a greater maximum modal gain that leads to lower threshold current density and higher differential modal gain, which is good for the application of p-doped 13 μm InAs/GaAs QD lasers in optical communications systems.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2009, 58 (3): 1901-1907. doi: 10.7498/aps.58.1901
Based on the density functional theory, the geometries, electrical structures and optical properties of Co-doped MgF2 system （Co:MgF2） are studied by first-principles ultra-soft pseudopotential plane-wave approach. With Co-doping increasing, a tetragonal-rhombic structural transition is obtained in Co:MgF2 The band gap decreases with increasing Co-doping, and a semiconductor-conductor transition is observed. Also, the calculations show that the static dielectric constant and the absorption coefficient can be remarkably modulated by Co-doping, indicating the potential applications of Co: MgF2 optical system.
2009, 58 (3): 1908-1916. doi: 10.7498/aps.58.1908
The geometrical and electronic structures, and also the dopant formation energies, lattice constants, band structure and density of states （DOS） of Sr1-xYxTiO3 with x=00, 0125, 025 and 033 are calculated from the first principles of plane wave ultra-soft pseudo-potential method based on density functional theory. The results of dopant formation energy show that Y preferentially enters the Sr site in SrTiO3 Electronic structure results show that pure SrTiO3 is an insulator and the Fermi energy is at the top of valence band. When doped with Y, the Fermi energy of the system goes into the conduction band and the system undergoes an insulator-to-metal transition. Due to the appearance of the carrier impurity from Y doping, there is a significant distortion near the bottommost conduction bands.
2009, 58 (3): 1917-1923. doi: 10.7498/aps.58.1917
The geometrical structure of Cu doped 32-atom supercell of AlN was optimized by using the ultra-soft pseudopotential method of total-energy plane wave based on density functional theory （DFT） . Density of states，band structure and optical properties were calculated and discussed in detail. The results revealed that The Cu dopants were found spinpolarized. Band structures show a half metallic behaviour. The band gap of Cu-doped AlN reduced and the absorption ability to infrared visible light strengthened obviously,the loss of energy decrease The ferromagnetic ground state in Cu-doped AlN can be explained in terms of p-d hybridization mechanism. These results suggest that Cu-doped AlN may present a promising dilute magnetic semiconductor.
First-principles study of the adsorption energy and work function of oxygen adsorption on Ni(111) surface
2009, 58 (3): 1924-1930. doi: 10.7498/aps.58.1924
The adsorption of atomic oxygen on the Ni（111） surface has been systematically investigated through first-principles DFT-GGA methods in wide ranges of coverage. It was found that the fcc hollow site is the energetically most favorable for the whole coverage range considered. The adsorption energy decreases with the coverage θ，while the work function increases linearly with the coverage.It can be also concluded from analysis of the electron density and projected density of states that the electron transfer from the substrate （Ni atoms） to the O atom gives rise to the appearance of a dipole moment, which results in a large increase in the work function. The O—Ni interaction between Ni 3d and O 2p orbitals results in the formation of bonding and antibonding states, while the antibonding states are hardly occupied. Therefore, the bonding interaction between O and Ni is stonger, and the adsorption energy is larger.
2009, 58 (3): 1931-1935. doi: 10.7498/aps.58.1931
The external force can make a graphene sheet tighten and change its electronic structure. By using the tight-binding method, the energy bands of graphene sheets with zigzag shaped edges and armchair shaped edges drawn by the tensile force are investigated based on considering the nearest-neighbor interaction, and the analytic relations between the energy gaps besides the energy bands of π-electrons for two types of graphene sheets and the tensile force are obtained . Through numerical calculation, we found that the energy gaps broaden as the tensile force increases besides that the tensile force can make graphene open an energy gap,and moreover, the energy gap of graphene with zigzag edges broadens more easily.
Atomistic simulation of mechanical properties of martensitic transformation under dynamic compression
2009, 58 (3): 1936-1941. doi: 10.7498/aps.58.1936
Molecular dynamics simulation （MD） was used to investigate the microscopic mechanism of martensitic transformations in Fe single crystals driven （along ［001］ orientation） by an accelerating piston. Simulated results revealed that the above compression process can be divided into five stages, namely the elastic compression, softening of elastic ratio, phase transformation （bcc to hcp）, over-relaxation of stress and elastic compression of high-pressure phase. The slipping laws of atoms and properties of stress are analysed in detail. Atoms can only slip along longitudinal direction under elastic compression, and when the longitudinal stress is beyond 10 GPa, local atoms begin to slip along lateral direction and form embryos, which is just the microscopic nature of the softening of elastic ratio.The stacking fault （fcc） is a more steady origin of crystal nucleation than the twin boundary. After the phase transformation, the atoms undergo an over-relaxation of stress （i.e., the lateral stress is larger than the longitudinal stress）, and this state disappears when the longitudinal stress is beyond about 36 GPa.
2009, 58 (3): 1942-1947. doi: 10.7498/aps.58.1942
Electromigration in Sn30Ag05Cu flip chip solder joints was investigated under a current density of the order of 104 A/cm2. The transfer of atoms or vacancies and the formation of Joule heating induced by electromigration were studies in terms of microstructural evolution. The formation of pancake-type void at the interface between solder and intermetallic compound was dominated by current concentration and the directional transfer of vacancies induced by electromigration. Series of voids were also found at the interface between Ni（P） finishes and solder joint. The area of voids at substrate side are less than that at chip side. The flux of Cu atoms in the pad has the same direction as the electron flux. The transfer of Cu atoms from pad to solder joint led to the formation of large areas of intermetallic compound in solder joint, and the amount of intermetallic compound increased along the direction of electron flux.
2009, 58 (3): 1948-1953. doi: 10.7498/aps.58.1948
The translational symmetric associated with photonic crystal is absent in the rotationally symmetric quasiperiodic photonic crystal （QPCs）, and the quasiperiodic photonic crystal has more defect modes than photonic crystal because of it. In this paper, we investigate the defect modes in the 12-fold quasiperiodic photonic crystal by the multiple scattering method. We find that there is a directional defect mode in quasiperiodic photonic crystal. When the defect rotates against the centre of the symmetry, there emerges a new defect mode.
2009, 58 (3): 1954-1958. doi: 10.7498/aps.58.1954
We present the design and fabrication of 13 μm vertical-cavity surface-emitting lasers （VCSELs）. This laser exhibits continuous-wave single-mode operation up to 82℃. The theshold current as low as 051 mA and a slop efficiency of 029 W/A have been achieved. This laser is composed of a wafer-bonded GaAs/Al（Ga）As distributed Bragg reflector （DBR） and a dielectric SiO2/TiO2 DBR with InAsP/InGaAsP strain-compensated multi-quantum wells grown in the cavity. The effect of cavity mode-gain offset on device performance is then discussed.
2009, 58 (3): 1959-1965. doi: 10.7498/aps.58.1959
The relations between the buffer leakage current and the characteristics of nucleation layer of AlGaN/GaN heterostructure have been obtained by comparative study of depletion capacitance of C-V characteristics in GaN-based heterostructure. The results showed that, the heterostructure material based on a sapphire substrate with a low-temperature GaN nucleation layer and SiC substrate with a high-temperature AlN nucleation layer have smaller buffer leakage current and lower carrier concentration of the background GaN buffer layer than that based on a sapphire substrate with a low-temperature AlN nucleation layer. A thorough analysis shows that, there is an n-type GaN conductive layer near the GaN/substrate interface in buffer layer based on the thinner nucleation layers. Contrarily, high resistivity GaN buffer layers appear in heterostructure materials based on thicker nucleation layer. One of the main causes of device leakage is the n-type GaN conductive layer. Appropriately improving the quality and thickness of nucleation layer can effectively reduce the carrier concentration, raise the resistivity and suppress the leakage current of the GaN buffer layer.
2009, 58 (3): 1966-1970. doi: 10.7498/aps.58.1966
The effect of recessed-gate depth on device characteristics was analyzed. The device characteristics with different recessed-gate depth were simulated by using SILVACO and the variation of saturation current, maximum conductance and threshold with different recessed-gate depth were obtained. With increasing recessed-gate depth, the saturation current reduces and maximum conductance increases and the threshold shifts to positive direction of X-axis. High electron mobility transistors of AlGaN/GaN heterostructure grown on sapphire substrates with different recessed-gate depth were fabricated. The simulation of different recessed-gate depth device characteristics were validated by comparing experiments with the simulation results. The discrepancies between simulation and experiment were analyzed in the aspects of etching damage and interface states.
2009, 58 (3): 1971-1979. doi: 10.7498/aps.58.1971
Based on energy dispersion relation of the deformed single-walled carbon nanotubes （SWCNTs）, various curves of the electronic velocity and effective mass of the lowest conduction band versus deformation parameters for SWCNTs are computed. It is found that only when a deformation occurs in the special direction（s） and is limited to a region of low deformation （the deformation parameter ε≤002）, the variations of the electronic average velocity vmean and average effective mass m*mean of different types of SWCNTs are very small （the relative variation≤2%）, which suggests that in these cases the electronic transport properties for SWCNTs under a low bias are basically stable. Whereas in other cases the electronic average velocity, or electronic average effective mass, or both of them vary significantly, even change in a dramatic way. This means that the electronic transport properties for SWCNTs under a low bias are unstable, even extremely unstable.
2009, 58 (3): 1980-1986. doi: 10.7498/aps.58.1980
Silver nano-structures were synthesized through thermal evaporation. Scanning electron microscopy （SEM） observations showed that the silver nano-structures had several types of morphology. The optical properties of silver nano-structures were obtained by ultraviolet-visible spectrometry, which shows the resonance wavelength of surface plasmon. In this work, we demonstrate the surface enhanced Raman scattering （SERS） signals which allow us to track down the surface plasmon local field spectra of Ag nano-structures. To prove it, we also used rhodamine 6G deposited on samples. As a result, we show that the transmittance spectra and SERS enhancement gives a complete description of optical and electric field caused by surface plasmon resonance of Ag nano-structures. The difference of Raman enhancement also indicates that different structures give different surface plasmon intensity when combined with the result of SEM.
2009, 58 (3): 1987-1991. doi: 10.7498/aps.58.1987
Impurities and deep levels in CdS/CdTe thin film solar cells with no back-contact layer were studied by deep level transient spectroscopy and photoluminescence. They could lower the device performance notably. Distribution of net carrier concentration was obtained. Two deep levels at Ev+0.365 eV and Ev+0.282 eV were determined with concentration of 1.67×1012 cm-3 and 3.86×1011 cm-3, respectively, and with capture cross section of 1.43×10-14 cm2 and 1.53×10-16 cm2, respectively. They are attributed to chemical impurities like Au and/or a singly charged tellurium vacancy complex, or related to O atoms introduced by the deposition of CdTe in O2 and Ar ambient.
2009, 58 (3): 1992-1996. doi: 10.7498/aps.58.1992
Soluble small red molecule No. 2 was introduced as the emitter for light-emitting diodes （PLED） with different cathodes. N-arylbenzinmidzoles （TPBI） was used as hole-blocking layer （HBL） to lower cathode barrier and facilitate electron injection.With TPBI/Ag cathode， the quantum efficiency was increased by 57%.The reason for the efficiency increase is that interfacial dipole layer was formed at the interface between TPBI and Ag, and possibly coordinated reaction between Ag and N atom in TPBI leads to a superior contact between TPBI/Ag.
2009, 58 (3): 1997-2001. doi: 10.7498/aps.58.1997
La067Ba033MnO3 thin films were grown on LaAlO3 substrate using pulsed laser deposition. The microstructure, magnetic and electrical properties of as-grown, annealed and CO2-laser-irradiated （CLI） LBMO films were studied. It is found that, after laser irradiation, the enhancement of the crystallinity of the film is accompanied by the emergence of the plain-like surface morphology with smaller roughness. The structure and magneto-transport properties of LBMO films are markedly improved in several dozens of seconds via CO2 laser irradiation. Compared with the annealing treatment, laser irradiation is a fast and effective way to tailor CMR manganites for industrial applications.
2009, 58 (3): 2002-2004. doi: 10.7498/aps.58.2002
La067Sr033MnO3 thin films have been deposited by laser molecular beam epitaxy system on glass substrates. The measurement of X-ray diffraction shows that the La067Sr033MnO3 thin film is a good orientation of c axis，and the magnetoresistance values of -378%, -268% and 607% at 88, 220 and 300 K, respectively, under 3 T magnetic field were observed.
Magnetomechanical modeling of magnet immersed in magnetic fluid and controllability of self-suspension
2009, 58 (3): 2005-2010. doi: 10.7498/aps.58.2005
A magnet stably suspending in magnetic fluid is influenced by several factors. The key to analyze prerequisites of suspension of immersed body in magnetic fluids is the establishment of an exact mathematical model. The magnetomechanical modeling of spherical magnet encased in spherical vessel is established. The influence on magnetic force by magnetic conductivity, remnant magnetism and radius of magnet, radius of container and off-centering of magnet is analyzed. The conclusion has universal character. The calculation results indicate that various parameters has inerratic influence to magnetic force, and the conditions for self-suspension always exist. The relation between various parameters and the self-supension position is discussed on the basis of analyzing features of suspension balance position, and methods of controlling self-suspension position are discussed.
2009, 58 (3): 2011-2017. doi: 10.7498/aps.58.2011
In this work, the electronic structure and the stability of ferromagnetism of C-doped ZnO are studied by first-principles calculations and Monte Carlo simulation. The calculated results indicate that the ferromagnetic ground state is stabilized by its half-metallic electronic structure which originates from the strong hybridization between Zn-3d and C-2p electrons. Meanwhile, by using the coupling strength obtained from first-principles calculations and Monte Carlo method, the Curie temperatures of ZnO1-xCx （x=555%, 833% and 125%） are predicted to be 210, 260 and 690 K, respectively, which is generally consistent with theroetical and experimental results. The electronic transfer resulting from C doping, and the changes between spin-up and spin-down electron changes for s, p and d electrons of C, Zn, O atom are analyed in detail. The simulated results show that, the local magnetic moments of ZnO1-xCx originate mainly from the hybridization interaction between Zn-3d and C-2p electrons, while the magnetic coupling between the local magnetic moments is preferentially the RKKY coupling.
Synthesis and magnetic, optical properties of Co doped ZnO room-temperature ferromagnetic semiconductor
2009, 58 (3): 2018-2022. doi: 10.7498/aps.58.2018
Co-doped ZnO polycrystalline was synthesized with sol-gel method. Room temperature ferromagnetism （FM） was observed in the synthesized sample. Studies onits structural and optical properties indicate that the FM is originated from the Co substitution for Zn in ZnO crystalline lattice, and the temperature of sample synthesis significantly affects the FM and photoluminescence of the corresponding samples, suggesting that Zn interstitial could be responsible for the origin of the FM.
2009, 58 (3): 2023-2029. doi: 10.7498/aps.58.2023
By investigating the spin configuration in ferromagnetic multilayer under stress field, the dependence of magnetoresistance （MR） upon the stress field in the ferromagnetic multilayer is discussed. The stress field can induce MR, and the MR strongly depends on both the value and the direction of the stress field. Generally, for the case of J>0, the stress field dependence of MR is closely related with the differences in magnetostriction and magnetocrystalline anisotropy between two ferromagnetic layers. When the stress field deviates from the magnetic easy axis lowards the magnetic hard axis, the MR first increases slowly, and then decreases rapidly. For a given direction of stress field, the MR first increases rapidly, later decreases slowly with stress field increasing. Moreover, when the direction of stress field approaches that of the hard axis, the dependence of MR upon both the value and the direction of the stress field becomes obvious. Especially, if the direction of the stress field is perpendicular to the easy axis, change of MR can double its value with the stress field increasing. When the stress field Hλ meets the condition 8πM/5≤Hλ≤18πM/5, MR increases monotonically, and the giant magnetoresistance （GMR） occurs. In the case of JJ>0.
2009, 58 (3): 2030-2034. doi: 10.7498/aps.58.2030
The relationship between the magnetic properties and the microstructure of Pt-Co permanent magnetic alloys was studied. X-ray diffraction （XRD） results indicated that the as-cast Pt-Co alloy has a texture microstructure. According to the scan electron spectrum （SEM） results, the as-cast alloy has a columnar structure and the columnar crystal grows along the cooling direction. After plastic deformation and recrystallization, the texture was disappeared and the grains became smaller and more uniform. Compared with the columnar structure of Pt-Co alloys, the magnetic properties of the recrystallized alloys were improved obviously. So the grain size and direction may be the main factors which can affect the coerivity of Pt-Co alloys.
2009, 58 (3): 2035-2041. doi: 10.7498/aps.58.2035
At present, the time domain dielectric spectroscopy is mainly used to analyze thin liquids or materials composed of molecular orderly substances. The various relaxation processes need to be unrelated or be superposed linearly. But it will be clearly limited when the method is applied to the complex heterogeneous mixture analysis. In order to widen its scope of application, the analysis method is improved in this paper by using the wavelet transform. Through the analysis of the oil-water mixture, the experimental results show that the time domain dielectric spectroscopy based on wavelet transform can not only offer the whole spectral information but exhibit the time domain and frequency domain information of various components. Therefore, the analysis method of time domain dielectric spectroscopy based on wavelet transform can be used to analyze complex heterogeneous mixtures.
2009, 58 (3): 2042-2048. doi: 10.7498/aps.58.2042
Hydrogenated amorphous a-SiC:H and a-SiCN:H with different nitrogen-concentration dielectric barrier films are prepared using the plasma-enhanced chemical vapor deposition technique （RF-PECVD）. The chemical and structural nature, mechanical property, dielectric constant and copper diffusion property of these films are characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy measurement, nano-indentation, Agilent 4294A precision impedance analyzer, Auger electron spectroscopy and field emission transmission electron microscopy. The results indicated that the dielectric constand of the film can be adjusted btween the values of 38 and 52 by controling the NH3/3MS ratio. With the increasing of NH3/3MS ratio, the concentration of Si-N and C-N bond structure is gradually increase and micro-structure of the film becomes more dense, which is the mechanism of the improvement in the mechanical property, thermal stability and copper diffusion property of the a-SiC:H based film produced by N-doping.
2009, 58 (3): 2049-2055. doi: 10.7498/aps.58.2049
The structure of 2D rods PhC CCW is studied, and it is found that the group velocity discreases quikly with the increase of lattice number between two rod defects. When 7×7 supercell unit is chosen, the largest group velocity νg-max of the guided mode is about 1/251 times that of photonic crystal line defect waveguide. Radius of the four rods around the cavity of the 7×7 supercell unit are adjusted, νg-max of the new strcture can reach 589×10-4c, and it's about 1/5 that of unadjusted structure. Finally, by making comparisons, it is found that the structure has the best slow-light characteristic when the radius of the up and down rods are changed.
2009, 58 (3): 2056-2060. doi: 10.7498/aps.58.2056
We study the intrinsic optical bistability（OB） of nondilute suspensions of coated spherical particles with a metallic core and a nonlinear dielectric shell. In this kind of system， as the spatial local field is not uniform, it cannot be obtained exactly. In this connection，we establish the self-consistent mean field approximation， and obtain the spatial average of the local field squared in the core as a function of the external applied field. Numerical results show that the optical bistability（OB） is dependent on the temperature T， the structural parameter k， and the volume fraction f. For given k and f， the width of optical bistability decreases with increasing temperature. At further increasing of T， OB is found to vanish. On the other hand， for given T and f， the bistable region gradually increases as the structural parameter k increases， accompanied with the increase in both the upper and lower threshold fields. More exactly， the increase of the bistable region mainly results from the rapid increase in the upper threshold field.
Studies on the dynamic process of up-conversion green emission from Er3+ under square wave excitation
2009, 58 (3): 2061-2066. doi: 10.7498/aps.58.2061
The rise and decay curves of Er3+2H11/2 and 4S3/2 upconversion emission in oxyfluoride tellurite glass were measured under the excitation of 808 nm and 980 nm light from laser diodes driven by square wave. Different rise times under 808 nm and 980 nm excitation reveals different excitation paths. Relationship between build-up process of the upconversion emission and lifetime of the intermediate state was analyzed with the rate equations. Excitation processes of the green upconversion emission under 808 nm and 980 nm excitation were confirmed. Square wave excited upconversion emission may also be used for measuring lifetimes of infrared energy levels with a conventional photomultiplier tube.
2009, 58 (3): 2067-2071. doi: 10.7498/aps.58.2067
Polarized green electroluminescence has been achieved at the peak wavelength of 550 nm from alternate copolymer poly （9, 9-dioctylfluorene-alt- benzothiadiazole） （PFBT）, which was synthesized by polycondensation. The liquid crystalline state of this copolymer under certain thermal treatment results in the uniaxial orientation of the conjugated backbones on an alignment layer. A rubbed-hole injection layer poly（3,4-ethylenedioxythiophene）:polystyrenesulfonate （PEDOT:PSS） was utilized as the alignment layer. Polarized absorption and photoluminescence spectra indicate the good alignment of the copolymer films with an ordering parameter of 075. Polarized polymer light-emitting diodes were fabricated with the structure of ITO/PEDOT:PSS/PFBT/LiF/Al. An electroluminescence polarization ratio of about 4 was achieved at a voltage of 15 V, with the luminance of 450 cd/m2 and luminous efficiency of 021 cd/A.
2009, 58 (3): 2072-2076. doi: 10.7498/aps.58.2072
SiN-based multilayer light-emitting devices, which employed Si-rich SiNx/N-rich SiNy multilayer as luminescence active layer, were fabricated by plasma enhanced chemical vapor deposition （PECVD）. Strong visible electroluminescence （EL） from the devices was observed at room temperature. By adjusting the Si/N ratio of the barrier layer, the effect of barrier on the electroluminescence properties was further investigated. The experimental results show that the performance of the devices can be significantly improved by controlling the Si/N ratio of the barrier layer.
Experimental differential investigation of state-selective single electron capture in slow He2+-He collisions
2009, 58 (3): 2077-2082. doi: 10.7498/aps.58.2077
State-selective single electron capture in He2+-He collisions at energies ranging from 20 to 40 keV have been studied experimentally by means of cold target recoil ion momentum spectroscopy. The differential cross sections have been obtained by measuring the longitudinal and transverse momenta of recoil ions. The results show that single electron capture into L shell is the dominant reaction channel, which was qualitatively explained with reaction window theory. The measured state-selective cross sections agree with the semi-classical close-coupling calculations, but have some deviations from the results of photon emission measurement. Total angular differential cross sections show that the single electron capture into ground state mainly contributes at small angles, and the single electron capture into excited states contributes at large angles. The oscillating structures of angular differential cross sections are observed, and can be understood by the interference of molecular orbits during the collision processes. The measured angular differential cross sections are compared with other experiments and the quantum-mechanical calculation.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2009, 58 (3): 2083-2089. doi: 10.7498/aps.58.2083
We performed first-principles calculations for the pressure-induced martensitic phase transition from the ground state ferromagnetic bcc phase to a nonmagnetic hcp phase in Fe under hydrostatic and non-hydrostatic pressure based on density-functional theory, employing the pseudopotentional and plane-wave method. The calculated results show that the magnetic moment of bcc iron under non-hydrostatic conditions decreases faster than that under hydrostatic conditions as the stress increases from 0 GPa to 18 GPa. Theoretical calculations prove that non-hydrostatic conditions can significantly reduce the bcc phase to hcp phase transition pressure. The critical stress for bcc-to-hcp transformation decreases linearly as the non-hydrostatic effect increases. The physical origins of the influence of non-hydrostatic pressure on the transition pressure are discussed.
2009, 58 (3): 2090-2096. doi: 10.7498/aps.58.2090
For a silo with unfixed wall, the pressure on its bottom will increase linearly with the height of granular material filled in it. Because no Janssen stress saturation occurs, its mechanic states differ from that of usual silo. By vertically pulling and pushing the wall of the silo, we measured the maximum static friction force of the wall, as functions of the load applied on the silo top and the mass filled in the silo. It is observed that the force increases with the mass, linearly for the pulling case, while exponentially for the pushing case, of which value for the latter may be one order of magnitude larger than that for the former. The force also increases with the load, linearly for both cases. The measurements can be well fitted with the theoretical results of continuous mechanics, assuming that ratio between horizontal and vertical stresses keeps the same everywhere inside the silo. The results support that the assumption made by Janssen for usual silo also suitable for the silo which has no stress saturation.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2009, 58 (3): 2097-2105. doi: 10.7498/aps.58.2097
On the basis of the two-dimensional Poisson process theory and spatial point process theory, we introduced the algorithm of cluster extraction which is based on k-th order distance, aiming at determining the valid range of the algorithm. We found that the ratio of cluster and cluster's densities and the number of data both have effect on the method. But the effect of the former much bigger than that of the latter. Furthermore, we introduced the concept of weight to extend the range of the simulated data, and gave the data different weights for delineating clusters, so that the range of this algorithm can be extended.
2009, 58 (3): 2106-2112. doi: 10.7498/aps.58.2106
Using a method of calculating the entropy based on the relativity of spatial fields to give a correlative index having the statistic characteristic of discrete spatial fields, we discuss the inherent rule of drought/flood and their spatial distributions in China. The result gives the associations of drought/flood distributions from 1470 to 2000, and shows that the actual relativity of drought/flood distributed fields is relative and not stochastic, being different from the random distributed fields, by calculating their entropy and matrix latent values. The every year's entropy shows the degree of the year's association with other ones. The greater the entropy is, the bigger the degree is, and vice versa. The similitude of climate state has a steady and obvious quasi-periodicity before 1820, whose size is about 113 years. After 1820, the size adds up to 130 years and the intensity is weakened. Another steady quasi-periodicity is 68 years, which is obvious from 1595 to 1820, and its size is changed from 61 years to 81 years. In other periods, the 68-year periodicity is not found obviously.
2009, 58 (3): 2113-2120. doi: 10.7498/aps.58.2113
A temperature correlation matrix is constructed by NCEP/NCAR reanalysis temperature data of 1948—2005, and the 99% confidence test is used to filter out correlation ‘noise'. We smooth the temperature data with step=5 d,10 d,… and construct correlation matrixes, and find that 365—730 d maybe a turning of time scale of temperature. Global average correlation coefficient Cglobal increases along with step size, but the rate is slower and slower. The positive correlation center（1625°W—775°E，75°N—125°S）（Area Ⅰ） and the negative correlation center（1575°W—325°E，275°—475°N）（Area Ⅱ） are the two areas we concern with, there is strong negative correlation between them. With the help of a 10a slipping window, we find that those 10a Cglobal had an abrupt change between 1981—1987a, and so did Area Ⅰ and Ⅱ. The points of strongest negative correlation on the North Pacific Ocean have been changing from 1948 to 2005.