Vol. 54, No. 2 (2005)
2005-01-20
GENERAL
2005, 54 (2): 483-489.
doi: 10.7498/aps.54.483
Abstract +
In this paper, by using the improved tanhmethod, the hybridlattice system an d Ablowitzladiklattice system are reduced to nonlinear algebraic equations, and then the new exact solutions for these equations, which include exact soliton wave solutions and periodic solutions, are obtained through solving these nonlinear algebraic equations.
2005, 54 (2): 490-495.
doi: 10.7498/aps.54.490
Abstract +
Using the Lie symmetry under infinitesimal transformations in which the time is not variable, the Hojman's conservation theorems for Raitzin's canonical equations of motion of nonlinear nonholonomic systems are studied. The differential equations of the systems and the determining equations of Lie symmetry under infinitesimal transformations are given. The Hojman's conservation theorems of the systems are established. Finally, we give an example to illustrate the application of the result.
2005, 54 (2): 496-499.
doi: 10.7498/aps.54.496
Abstract +
In this paper, the symmetries of Lagrange system and Hamilton system have been studied. It is indicated that two kinds of description of Mei symmetry are equiva lent for Lagrange system ,so only one kind of Mei symmetry can be given; however , they are not equivalent for Hamilton system, so two kinds of Mei symmetry can be given.
2005, 54 (2): 500-503.
doi: 10.7498/aps.54.500
Abstract +
Two kinds of Mei symmetries and conserved quantities of a mechanical system in phase space are studied. The definitions of the two kinds of Mei symmetries of me chanical system in phase space are given. The determining equations and conserve d quantities are obtained. An example is given to illustrate the application of the result.
2005, 54 (2): 504-510.
doi: 10.7498/aps.54.504
Abstract +
In this paper, we solve the (2+1)dimensional dispersive long wave equation by using a new modified algebraic method, and obtain abundant new exact solutions. These solutions contain solitonlike solutions, periodiclike solutions,hyperboliclike function solutions, Jacobilike elliptic function solutions and so on.
2005, 54 (2): 511-516.
doi: 10.7498/aps.54.511
Abstract +
The Schrdinger equation of forced timedependent harmonic oscillator is solved by using the explicit Euler method. The result of evolution of the initial state is given, the feasibility and applicability of explicit Euler method are discussed. Using coherent state, the nonadiabatic berry phase and the cyclic initial states of the system are discussed.
2005, 54 (2): 517-521.
doi: 10.7498/aps.54.517
Abstract +
Based on practical implementations of quantum cryptography with the attenuated laser pulses as the signal source rather than single photon, as well as lossy channels, detection efficiency, dark count of singlephoton counter, and technological possibilities of a realistic eavesdropping, we discuss a combining eavesdropping strategy of Breidbart basis and beamsplitting, and give a bound on maximum disturbance for a given mean photon number and transmission length for which a secret key can be distilled.
2005, 54 (2): 522-529.
doi: 10.7498/aps.54.522
Abstract +
A closed solution of the Schrdinger equation for a timedependent two coupled harmonic oscillators including a driving part and a twomode coupled part is derived by adopting the LewisRiesenfeld invariant theory and properly chosen Hermitian invariant operators. The evolution operator of the system and the condition for generating twomode squeezed states are obtained. It is shown that the quantum fluctuation of squeezed states of the system is independent of the driving part, but depends on the initial states of the system.
2005, 54 (2): 530-533.
doi: 10.7498/aps.54.530
Abstract +
Using the improved brickwall model,the writers of the article have made some researches in the contribution made by the high spinning gravitation field to static ballsymmetry black hole entropy. The research shows that in the static ballsymmetry black hole, the quanta entropy of the gravitation field in whitch the spinning is 2 is still in direct proportion to the horizon. When the same truncatin genes as theose in scalar guantity field are selected the quanta entropy is two times in scalar quantity field, and foursevenths of those in Dirac field.
2005, 54 (2): 534-542.
doi: 10.7498/aps.54.534
Abstract +
A new measure of complexity for finite symbol sequences, named as lattice comple xity, is presented, based on LempelZiv complexity and the symbolic dynamics of onedimensional iterated maps system. To make lattice complexity distinguished from LempelZiv measure, an approach called finegraining method is also prop osed. When finegraining order is small enough, the two measures are almost equ al. When finegraining order goes to large, the differentiation between them be comes apparent. Applying these measures to studies of logistic map, we find thos e be regarded as complex sequences by lattice complexity are clearly generated a t the edge of the chaotic region. The derived properties of the measures are als o discussed.
2005, 54 (2): 543-549.
doi: 10.7498/aps.54.543
Abstract +
In this paper, a semiconductor laser with external optical feedback is entered into chaotic motion by increasing the time of the external optical feedback at first. And then, the sliding mode variable structure control scheme is used to control the chaotic motion of this laser system. The advantage of this method is that the stable output laser can be obtained in a short time and the output power strength of the laser can be adjusted flexibly in accordance with the engineering requirement. Theory analysis and simulation results show that the results of the control have powerful stability and robust .Our research results have many helpful values to improve the speed of stable output, flexible adjustment of laser output power as well as efficiency of energy transformation for real laser system.
2005, 54 (2): 550-556.
doi: 10.7498/aps.54.550
Abstract +
We have studied the determination of delay time and embedding dimension for phase space reconstruction of chaotic time series using the information theory. We use the symbolic analysis method to compute mutual information for determining the delay time. Furthermore we also present an information theory approach to determine embedding dimension. That is, we determine the embedding dimension by considering the variation of the conditional entropy of the reconstructed vector with its dimension. Numerical simulations verify that the method is applicable for determining an appropriate embedding dimension.
2005, 54 (2): 557-564.
doi: 10.7498/aps.54.557
Abstract +
This paper studied the characteristics of stochastic resonance in the neighborhood of bifurcation point of two nonlinear dynamic systems, the pitchfork bifurcation system and FitzHughNagumo (FHN) cell model. The results of research show t hat the two nonlinear dynamic systems have the same bifurcation characteristic o f transition from one to two attractors (or from two to one attractors) when the bifurcation of each system occurs, that is, in the neighborhood of the bifurcat ion point there exist attractors before and after bifurcation on the both sides of the bifurcation point. Under the perturbation of noise, a transition may occu r between the two coexisting attractors on the right side of the bifurcation poi nt, in a way like the mechanism of traditional stochastic resonance; moreover,an other transition may also occur among the three attractors (one before bifurcati on and two after it) on two sides of the bifurcation point, which can induce sto chastic resonance alone. When the two types of transitions occur, the stochastic resonance induced by the second type of transition continues in a wide intensit y range of noise, which causes the first type of transition; and the stochastic resonance induced by the first type of transition stops in a rather small range of the noise intensity,and then causes the second type of transition.
2005, 54 (2): 565-573.
doi: 10.7498/aps.54.565
Abstract +
A new formula together with the computing method for calculating Madelung constant α is given, based on the parallelepiped neutral cells which are situated around the reference cell,of which 26 such cells constitute the first shell and 98, 218,…,24 N2+2 cells constitute the second, third,…, and the Nth shell respec tively. The α(N) is a rapidly converging series and can be calculated very easily. In this paper Madelung constants and madelung energy for some complex io nic crystals have been computed by this new method which can be applied to all k inds of complex ionic crystals of trigonal ,orthorhombic system and so on.
2005, 54 (2): 574-577.
doi: 10.7498/aps.54.574
Abstract +
A method is proposed for measuring the beat frequency of weak light based on pho ton correlation measurements. In contrast to conventional techniques this method is not limited by the response time of the detector or preamplifier, and can me asure frequencies on the order of 10GHz without the need of a frequency spectrum analyzer. Moreover, extremely low light intensities may be measured.
2005, 54 (2): 578-581.
doi: 10.7498/aps.54.578
Abstract +
The effects of H2O on the synthesis singlewall carbon nanotubes(SWCNTs)by decomposing CH4 in Ar at 800℃ were studied by TEM and Raman scattering. It is shown that the water existing in the reacting gas increases the percentage composition of the SWCNTs in the products. Preliminary analyses indicate that the water is involved in the purification course, and the generation of the amorphous carbon is brought about. Furthermore, the water can affect the distribution of the SWCNTs'diameter.
2005, 54 (2): 582-586.
doi: 10.7498/aps.54.582
Abstract +
Fabrication of nanopore arrays is of great importance in nanodevices manufacture and basic scientific research. Focused ion beam (FIB) and electron beam lithography (EBL) have been widely used for fabrication of nanostructures.However, it takes very long time to fabricate nanostructure patterns of large area. In this p aper we report a novel fast fabrication method for nanopore arrays of large area by FIB. Each pixel of predesigned BMP file is regarded as a fabrication dot. B y matching the pixel of the presigned BMP pattern with the required fabrication area, nanopore arrays of large area can be fabricated in a very short time.
ATOMIC AND MOLECULAR PHYSICS
2005, 54 (2): 587-593.
doi: 10.7498/aps.54.587
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The effect of the free electron background in plasmas is introduced in HartreeFockSlater selfconsistent field atomic model to correct the single electron energies for each electron configuration, and to provide accurate atomic data for BoltzmannSaha equation. In the iteration process chemical potential is adjusted to change the free electron background to satisfy simultaneously the conservation of the free electrons in Saha equation as well as in HartreeFockSlater selfconsistent field atomic model. As examples the equations of state of the carbon and aluminum plasmas are calculated to show the applicability of this method.
2005, 54 (2): 594-605.
doi: 10.7498/aps.54.594
Abstract +
Modern experimental methods or accurate quantum theory methods usually may obtain a vibrational energy subset［Ev］ containing m energies, but it may be very difficult to have all the excited highlying vibrational energies f or the electronic states of most diatomic molecules. Since the full vibrational spectrum and the molecular dissociation energies of the electronic states of Na 2 molecule are very important in many studies and applications, the vibrationa l spectroscopic constants and the full vibrational spectra of some electronic st ates of Na2 molecules are acqnired using the algebraic method (AM), and the di ssociation energy (DE) of these states are obtained using the algebraic energy m ethod (AEM). The results show that AM can give accurate vibrational spectroscopi c constants and correct full vibrational energy spectrum {Ev} from experim ental vibrational energy subset［Ev］, and the molecular dissociation energies obtained using the AEM have much better accuracy than those generated u sing the vibrational constants given in the literature. The AEM can give reliabl e values of the dissociation energies for some excited electronic states whose D E may not be available in the literture.
2005, 54 (2): 606-611.
doi: 10.7498/aps.54.606
Abstract +
Multicharged xenon ions with charge up to 20 have been observed in laser ionization of xenon beam by a 25ns Nd:YAG 1064nm laser with a laser intensity of 1011—1012 W·cm-2 Experimental results indicate that the multicharged ions appeared only when the laser interacted with the middle part of the pulsed beam, and its intensity increases with the increase of the backing pressure of Xe source gas. These indicate that the clusters in the beam is essential to the production of multicharged ions. We also discuss the possible mechanism of the generation of the multicharged ions.
2005, 54 (2): 612-616.
doi: 10.7498/aps.54.612
Abstract +
LaAlO3 and Ce: LaAlO3 single crystals were grown by the Czochralski technique. Infrared absorption spectrum, ultraviolet absorption spectra, and fluorescence spectra were measured at room temperature. According to the absorption spectra, the energy levels structure of Ce3+ in LaAlO3 single crystals was confirmed. The fluorescence spectra of Ce: LaAlO3 were explained using this structure.
2005, 54 (2): 617-621.
doi: 10.7498/aps.54.617
Abstract +
The real triggered single molecule source is recognized as an ideal single photon source with a Poissonian statistics background. By considering the effect of the triplet state in single molecule energy level, an explicit function is given for the signaltobackgound ratio(SBR) by use of photoncounting statistics. When PRS(1)2PRS(2)-3PRS(2), we present an effici ent method to determine the SBR of the triggered single photons source, which s hows SBR=P2RS(1)/2PRS(2).In addition, the expression of Q, as a function of signaltobackgound ratio, has been obtained. It turns o ut that this method is simpler and gives a greater accuracy than previous proce dures.
2005, 54 (2): 622-627.
doi: 10.7498/aps.54.622
Abstract +
The interactions between DNA and histone are studied by using the molecular combing method. With this simple but effective method, λDNA molecules are stretched to a length of 26—28 μm, 16—17 times of their contour length (～162 μm). After DNA binding of histones, DNA molecules are condensed and the lengths of the stretched complexes become significantly shorter, with length distribution peak lying between 10—14 μm. The lengths of the stretched DNAhistone complexes are closely related to the histone concentration and the mixing ratio of DNA base pair and dye molecule.
2005, 54 (2): 628-635.
doi: 10.7498/aps.54.628
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We present an optimum valence bond scheme to study stable geometric structures of clusters, by combining the characteristics of valence bonds and the first-prin ciple molecular dynamics simulation. With limited computational effort, we can o btain the properties of cluster Xm with m as large as possible, and th e properties of all clusters Xi (i
2005, 54 (2): 636-641.
doi: 10.7498/aps.54.636
Abstract +
By using timeofflight spectroscopy, the ionization and explosion of large argon clusters (n—=3×103-3×106) in the intense femtosecond pulsed lase r field (60 fs，2×1016 W/cm2) has been studied, and the dependence of a verage energy of ions emitted from argon clusters on the gas backing pressure ha s been measured. By comparing the average ion energies obtained with two differe nt supersonic conical nozzles and considering the Hagena's scaling law of clust ers, we have found that the average ion energy is determined by the cluster size when the laser parameters are kept unchanged. The experimental results indicate d that when the cluster size is less than 3×105 atoms per cluster, the Coulom b repulsion force is the dominating factor in the expansion mechanism. Beyond th is size, for 3×105
CLASSICAL AREA OF PHENOMENOLOGY
2005, 54 (2): 642-647.
doi: 10.7498/aps.54.642
Abstract +
The timedomain radiation characteristics of the resistanceloaded dipole ante nna with dielectric block parallelly connected to one side of the feeding region are studied by using finite difference time_domain(FDTD) method and perfectly m atched layer(PML) technique. It is found that this kind of antenna has very well directive property. The influences of the size and dielectric constant of the l oaded dielectric block on the radiation characteristics of the antenna are analy zed. The optimum structure parameters of antennas with very well directivity and enough efficiency are given. The low profile property of this kind of antenna m akes it easier to integrate with circuit. It is preferable for the ultrawide b and wireless communication system, such as UWB system, to use this kind of anten na.
2005, 54 (2): 648-652.
doi: 10.7498/aps.54.648
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Using the finite difference time domain (FDTD) method, the scattering of a lossy anisotropic plate is analyzed when the plate is illuminated by a plane transient electromagnetic wave. Based on the resonance characteristics of the back scattering RCS in frequency domain and the transient waveform of the back scattered electric field in time domain, a reconstruction scheme for recovering the transverse permittivity and conductivity for an anisotropic plate is proposed. The calculation results exemplify the availability and simplicity of the present scheme.
2005, 54 (2): 653-657.
doi: 10.7498/aps.54.653
Abstract +
Highorder correction to the fields of ultrashort, tightlyfocused laser pulses expressed in power series of ε=1/(ω0t0) and s=1/(k0w0)（ω0=ck0 the central oscillatory frequency, t0 the pulse duration, w0 the beam waist radius), are derived. Based on paraxial approximation, the firstorder correction terms to the Gaussian pulses are explicitly given. Their corrections of amplitude and phase, are found to be related to the variable of ε. Applying them to the study of the electron dynamics in the intense laser pulse field, we found that as long as ω0t0>20, the zerothorder approximation (long pulse approximation) is adequate for describing the interaction. For ω0t0<20, higherorder corrections have to be taken into account.
2005, 54 (2): 658-664.
doi: 10.7498/aps.54.658
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By using the Wigner distribution function(WDF)method,the fractional Fourier transform (FRFT) of beams is studied.HermiteGaussian (HG) beams are taken as an example; closedform expressions for the intensity distribution and beam widths of HG beams at the FRFT's plane are derived and changes in the intensity dist ribution of HG beams with the order of the FRFT are illustrated with numerical examples.It is shown that a symmetrical intensity distribution with equal beam width in the x and y directions can be achieved by a suitable choice of the transform order p.
2005, 54 (2): 665-668.
doi: 10.7498/aps.54.665
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Effect of interchain coupling on the inversed polarization of a biexciton has been studied in the framework of a tightbinding approximation. It was found that a biexciton state is mainly confined in one chain even the interchain coupling is included. The inversed polarization will be enhanced remarkably with the interchain coupling in the case of a weak nondegenerate confinement. However, the inversed polarization will keep nearly unchanged for a strong nondegenerate confinement.
2005, 54 (2): 669-676.
doi: 10.7498/aps.54.669
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We study the statistical properties of the image speckles produced by strongscattering objects in the 4f optical imaging system. Using the generic expression of the complex amplitude of speckles and the approximation of the doubleexponential function, we first obtain the ensemble average of the speckle intensity. Then we derive the variance of the speckle intensity based on the rotational transformation of the real and imaginary parts of the complex amplitude of speckles. We finally obtain the expression for the contrast of the speckles, which is explicitly related to the statistical parameters of random surface and to the parameters of the imaging system. Our results are an obvious improvement compared with those reported in the literature, where the relations including such implicit quantities as the average size of the scattering grains of the random surface and the number of scattering grains are usually used. The results of this paper would be helpful for the characterization of random surface by speckle contrast.
2005, 54 (2): 677-681.
doi: 10.7498/aps.54.677
Abstract +
A new x_ray imaging technique, diffraction_enhanced imaging, has been recently developed in Beijing Synchrotron Radiation Facility(BSRF). Diffraction_enhanced i maging is a radiographic technique that derives contrast from an object’s absor ption, refraction gradient and small_angle scatter properties(extinction). This imaging method may improve image quality for medical applications, industrial ra diography for non_destructive testing and x_ray computed tomography.
2005, 54 (2): 682-686.
doi: 10.7498/aps.54.682
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In this article, a new method to produce gratings with linearly variable spatial frequency is proposed and the expression of grating frequency is obtained. By inserting special lenses into the two light paths, the production of grating with linearly variable spatial frequency is realized. The modification of frequency can be easily achieved by properly adjusting the experimental parameters. The simulated hologram is given.
2005, 54 (2): 687-695.
doi: 10.7498/aps.54.687
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The quantum theory of polarizing light and the Stokes operators are applied to the study of the evolutions of polarization states of light in the processes of i nteraction with atoms in the case with or without Kerr medium. The non_classic b ehavior in the fluctuations of Stokes parameters for the polarizing light and th eir squeezing are investigated. The polarization ellipse, the degree of polariza tion of the field in quantum optics and the signal_to_noise ratio in the Stokes parameters are discussed. It is shown that the modulated oscillations appear in the evolutions of Stokes parameters and their fluctuations. These oscillations c ollapse and revive intermittently. The polarization ellipse does not vary in the interaction with atoms but the degree of polarization will oscillate. Kerr medi um changes these oscillations distinctly.
2005, 54 (2): 696-702.
doi: 10.7498/aps.54.696
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In this article, the dynamical properties in the system of two identical twolevel entangled atoms interacting with a binomial optical field are studied by means of time evolution operator and numerical calculations. The results show that the time evolution of atomic population and atomic dipole squeezing depends on the degree of entanglement of the initial two identical twolevel entangled atoms and the parameters of the binomial state optical field. The atomic dipole moment can be completely squeezed via choosing appropriate parameters of the system.
2005, 54 (2): 703-709.
doi: 10.7498/aps.54.703
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The dynamics of the two_photon Jaynes_Cummings model with atomic motion are studied by using the quantum information theory, and the quantum echanical channel representing the state change of atom is given; the quantum mutual entropy and reduced entropy of the atom are derived. The influences of the atomic motion and the field structure on the quantum mutual entropy are examined. It is shown that the properties of quantum mechanical channel are strongly dependent on the atomic motion, the field model structure, and the entanglement between the atom and the field.
2005, 54 (2): 710-714.
doi: 10.7498/aps.54.710
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The oscillation characteristics of populations in two orthogonal energy substates of semiconductor quantum dots (SQDs) excited by linearly polarized monochromatic pulse field were discussed. With rotatingwave approximation, the nondamped solutions of the dynamic population equations with resonance excitation were deduced. The effective transition dipole moments and effective input pulse area were introduced and their expressions were also given. Theoretical analysis showed that the amplitude and frequency of the population oscillation on the substates can be manipulated by adjusting the original conditions and the polarization angle of excitation field.
2005, 54 (2): 715-720.
doi: 10.7498/aps.54.715
Abstract +
The propagation of a Ni_like Ag x_ray laser operating at 139 nm is numerically simulated. A two_dimensional ray tracing code is used to investigate the refraction and saturation effects of the x_ray laser beam as a postprocessor of a one_dimensional hydrodynamic code. The x_ray laser beam trajectory in a plasma medium and the spatially integrated laser output intensity as functions of the plasma length are calculated. Numerical results show that the refraction effect plays an important role in the beam propagation and amplification process.
2005, 54 (2): 721-725.
doi: 10.7498/aps.54.721
Abstract +
A corner_pump method for high_power quasi_three_level lasers is reported. The de sign uses a slab laser configuration with the incident pump light from the slab corner. We present an analytic description of pumping absorption, pumping bright ness, doping concentration and crystal dimension for the corner_pumped composite Yb:YAG laser. In the experiments a maximum continuous-wave output power of 400 W with slope efficiency 28% was achieved. This result shows the validity of corn er_pumping concept and its feasibility in the development of high_power solid_st ate lasers.
2005, 54 (2): 726-735.
doi: 10.7498/aps.54.726
Abstract +
Based on the phaseconjugate polarization interference between two onephoton processes, we have studied theoretically the symmetric sumfrequency polarization beat (SFPB) of V type threelevel system in attosecond scale in the case of arbitrary bandwidth or broadband linewidth laser. The homodyne detected SFPB signal is shown to be particularly sensitive to the statistical properties of the Markovian stochastic light fields with arbitrary bandwidth. We have found that the accuracy in the measurement of the energylevel sum of two excited states which are dipolar forbidden transition to each other is determined by the homogeneous linewidths of the optical transitions and exceeds the laser linewidth. A Dopplerfree precision in the measurement of the energylevel sum can be achieved with an arbitrary bandwidth. The field correlation has weakly influence on the SFPB signal when the laser has a narrow bandwidth. When the laser has a broadband linewidth, the SFPB signal shows resonantnonresonant cross correlation. As an attosecond ultrafast modulation process, SFPB can be extended intrinsically to any sumfrequency of energylevels.
2005, 54 (2): 736-741.
doi: 10.7498/aps.54.736
Abstract +
The search for new methods to produce entangled photons is a subject of great interest in quantum optics. We show theoretically that two_photon entangled states may be generated through a cascaded nonlinear optical process in a quasiperiodic optical superlattice. When an idler photon ωi produced from spontaneous parametric down conversion (ωp=ωs+ωi) combines with a pum p photon to produce a sum frequency photon ωb(ωb=ωi+ω p), the latter is entangled with the remaining signal photon ωi. Both a pulsed and a cw 532nm laser have been used to pump a quasi_phase matched LiTaO 3 crystal to generate simultaneously 630nm signal photons through parametric d own conversion and 460nm sum frequency photons. The advantage of this method is that entangled photons of short wavelength may be produced.
2005, 54 (2): 742-748.
doi: 10.7498/aps.54.742
Abstract +
The two_cell stimulated Brillouin scattering (SBS) system that uses different media in generator and amplifier cells is investigated. It is demonstrated that th e seed light still has enough amplification when the Brillouin frequency shifts of this two media are near and their Brillouin line_widths are crossed. In exper iment, when CCl4 is used as an amplifying medium and liquid mixture of CCl4/ CS2 as generating medium, and the two_cell SBS system is pumped by Nd:YAG Qs witched laser, the influence of the deviation of Brillouin frequency shift on seed light Brillouin amplification is studied. The result shows that amplification efficiency and pulse compression ratio are still large enough when Brillouin frequency deviation is small. Moreover, under the condition of CS2 as the amplifying medium and benzene as the generating medium, seed light amplification efficiency of 44, pulse compression ratio of 72, phase_conjugation fidelity of 98%, and stability of seed light amplification efficiency of <3% are obtaine d.
2005, 54 (2): 749-754.
doi: 10.7498/aps.54.749
Abstract +
In this paper, high_order contrast is brought forward for studying small_scale self_focusing phenomenon in high_power solid state laser drivers. Based on the properties of semi_invariant, we obtain the analytic expressions of high_order contrast of near field of beams. Finally, we study the propagation of plane waves with PSD phase noise and obtain the evolution of fill factor, modulation, contra st, third_order contrast and fourth_order contrast with Bintegral value. C omparing the results of numerical simulation, we find that third_order contrast and fourth_order contrast are good parameters for characterizing the small_scale self_focusing phenomenon.
2005, 54 (2): 755-762.
doi: 10.7498/aps.54.755
Abstract +
For avoiding adverse effect arising from group velocity mismatching in parametri c amplification, a new method is presented, in which we combine pulse front slan t and noncollinear phase matching to completely compensate group velocity mismat ching of three pulses, in femtosecond optical parametric amplification (OPA). Th e change of the phase matching angle, the pulse front slant angle and the noncol linear angle with the signal wavelength are calculated, when group velocity matc hing of three pulses is achieved in BBO crystal type_Ⅰ and typeⅡ phase matching configurations. The effect of group velocity matching of three pulses on the spatial walk_off length, the parametric gain and the parametric bandwidth is analyzed. The results indicate that, using this method can make matching of gro up velocities of three pulses, when tuned continuously in both BBO type_I and Ⅱ phase matching femtosecond OPA, and thus the effective interaction length of th ree pulses is increased considerably. This calculation method and the analysis r esults provided a theoretical guidance for obtaining parametric pulses with high er gain and shorter duration.
2005, 54 (2): 763-767.
doi: 10.7498/aps.54.763
Abstract +
A new conception of effective gain recovery time of semiconductor optical amplifier (SOA) was brought forward, and a simple analytical expression for the gain r ecovery time was derived. Factors that affect gain recovery time, such as bias c urrent, probe power and device length were analyzed respectively on the base is of application of SOA to the cross gain modulation wavelength conversion. Gain r ecovery time was measured experimentally. It is shown that the experimental resu lt agrees well with the theoretical calculation.
2005, 54 (2): 768-772.
doi: 10.7498/aps.54.768
Abstract +
The metamaterials by use of L_C lumped_elements in the transmission line have the preternatural characteristic,which is different from the conventional dielectrics.We report the experimental results in the left_handed range with anti_parallel phase and group velocities in the metamaterials,with the negative refractive index, and we find the bandgap corresponding to zero averaged refractive index.The configuration offers some significant advantages:it is more compact in si ze,the material parameters can be tuned,and the method of fabrication is easy to carried out.
2005, 54 (2): 773-776.
doi: 10.7498/aps.54.773
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The principle of design of polarization band_pass filters used for wavelength d ivision multiplexing systems is presented. The design method is based on the con cept of thin_film photonic crystal superlattice. Two kinds of design are put for ward. One of them is to construct by superposition of two photonic crystals; and the other is to insert a new photonic crystal into the middle of a photonic cr ystal, so that there are in effect three photonic crystals. Such band_pass filte rs have excellent optical properties with p_polarization transmittance and s_pol arization reflectance. The characteristics of the filters, including peak transm ittance, half_band width and rejection are discussed.
2005, 54 (2): 777-781.
doi: 10.7498/aps.54.777
Abstract +
The dispersion in a chirped pulse amplifier (CPA) with a Martinez stretcher is analyzed theoretically based on ray_tracing. The method of mutual compensation th at introduced properly the negative third_order dispersion to balance the fifth_ order dispersion is presented. A shorter pulse near the transform_limit can be g enerated by this method rather than by the traditional approach that zeros the s econd and the third order dispersion successively in the CPA system.
2005, 54 (2): 782-788.
doi: 10.7498/aps.54.782
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Based on the bistability effect of nonlinear FP cavity (NOLF), a method is suggested to suppress the pedestal of ultra_short optical pulse compressed by dispersion shift fiber (DSF). The coupled mode equation is applied to analyze the chara cteristics of the pedestal suppression of NOLF. The results show that the pedest al energy ratio of transmitted pulse can be decreased to half of incident pulse through reasonably selecting the facet reflectivity of NOLF, the initial phase d etuning between the input pulse and NOLF, and the gain of Er_doped fiber amplifi er.
2005, 54 (2): 789-797.
doi: 10.7498/aps.54.789
Abstract +
Sound field separation technique has been proposed, which overcomes the limitati on on applications of near_field acoustic holography (NAH). The limitation is th at the sound field on one side of holographic plane must be free，that is to say , all the sound sources must be confined to the other side. Sound field separation technique with double holographic planes has been built according to the wave field extrapolation theorem and the superposition theorem of sound pressure scalar in wave_number domain, and the technique with single holographic planes has also been built according to Euler's formulation and the vector superposition theorem of particle velocity in wave_number domain. A particular feature of the technique is that the influence of background noise on reconstructed results can be removed while retaining the background noise in the holographic measurements. The derivation of the principle verifies the technique theoretically, and the computer simulations and experiment demonstrate its feasibility and effectiveness.
2005, 54 (2): 798-801.
doi: 10.7498/aps.54.798
Abstract +
We have investigated the distribution of two_dimensional granular flow in inclin ed channel and the distribution of the density of granular flux (ξ=ρ·ν) near the rough boundary walls. The results showed that the transverse distributi on of the density of granular flux is symmetric about the channel center, and th ere exists a strong extremum near the wall; the distribution of the density of g ranular flux near the walls is nonlinear with increasing inclination. In this paper, we turn attention to the effect of channel width on the distribution of the density of granular flux. There is a critical channel width for the distribu tion of the density of granular flux. In our experimental condition, the critica l width is 700mm (Wc=70d,d being the granular diameter), and there i s a weak extremum in the curve of the density of granular flux distribution when the channel width is in the range from 70 to 80d. When the channel width is smaller than the critical width, the density of granular flux can be expressed by ξ∝(sinθ)α with,032≤α≤085 the value of α is related with the channel width.
2005, 54 (2): 802-806.
doi: 10.7498/aps.54.802
Abstract +
Firstly,we choose a strata temperature gradient and start to compute.According to thermodynamic parameters,mud fluid parameters and well casing structure parameters etc.,the exit temperature of mud fluid can be obtained.By comparing the calculated value with the measured value of the exit temperature,we correct the chosen strata temperature gradient.Sequentially,we do above_mentioned works repeatedly until a proper strata temperature gradient is gained.Based on this,derived from the equations of thermodynamics and fluid mechanics,we can obtain the temperature variation along the depth of sidewall,and the mathematical model of distribution of strata temperature.Since mud fluid,rock and the temperature field are interactive and interfering during the process of drilling wells,the above technique provides a new method for investigating the theory and applications of the coupled thermal_hydrological_mechanical processes.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2005, 54 (2): 807-811.
doi: 10.7498/aps.54.807
Abstract +
It is shown in three different ways that the wave equation varying with time and the Helmholtz equation are equally effective for analysing the transmission of electromagnetic waves from the weakly ionized plasma in the plane geometry. Eve n when the scale length of plasma approaches the waves length, the electromagnet ic waves are still simple harmonic waves. The properties of transmission of elec tromagnetic waves from the weakly ionized and highly collisional plasma are stud ied numerically. The results show that the highly collisional plasma is a good m icrowave absorber.
2005, 54 (2): 812-817.
doi: 10.7498/aps.54.812
Abstract +
Using a two_fluid two_temperature hydrodynamic code, we studied the hydrodynamic s in the interaction of intense (1015W/cm2) ultrashort (150fs) laser pulses and linear density plasmas. The simulation results show the ponderomotiv e force effect on the formation of the electron density ripples in underdense re gion, such ripples increase the reflection of the laser pulse, and on the separa tion of the plasma in critical surface. Quasi_electroneutrality is not suitable in this case because of the different ponderomotive force and the gradient of th ermal_pressure for ions and electrons. Ions are moved by the electrostatic force . Comparing with the simulation results from one_fluid two_temperature code, we find that under strong ponderomotive force and gradient of thermo_pressure, two_ fluid code is more suitable to simulate the hydrodynamics of plasmas.
2005, 54 (2): 818-823.
doi: 10.7498/aps.54.818
Abstract +
Hydrogenated carbon thin films were fabricated on the surface of polyethylene terepthalate(PET) by radio frequency plasma enhanced chemical vapor deposition (r. f.PECVD).The film structure properties were studied by means of atomic force mic roscope(AFM), x_ray photo_electron (XPS), laser Raman spectroscopy, Fourier_tra nsform infrared spectra(FTIR),etc. The barrier property of the film was conducte d on the water vapor permeation instrument. The results show that nano_hydrogen ated carbon films have been deposited on PET surface and they are mainly compose d of sp2 and sp3 hybridized hydrogenated carbon compounds. Plasma pa rameters influence the films' growth rate and structure characteristics. The fil m reduces the water vapor permeation ratio of the PET by 7 times at a film thick ness of only 900nm.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2005, 54 (2): 824-831.
doi: 10.7498/aps.54.824
Abstract +
In this paper, the Cu(001) surface covered with glycylglycine has been studied by scanning tunneling microscope(STM) under ultra_high vacuum condition. On that surface copper clusters in nanometer_scale, which could form alphabet or graph a t our wishes, may be produced by the scanning of STM under a certain bias voltag e condition. The height of these clusters has a close relation with bias voltage , tunnel current and time. It offers the opportunity to fabricate nanometer_scal e apparatus by these clusters due to their stability at room temperature. The ex perimental result shows that the copper atoms which form these clusters come fro m neither copper substrate surface nor STM tip. We think that the tensile stress field in the copper substrate is produced due to the chemisorbed glycylglycine molecule in tunnel electric field and it is the migration of copper subsurface i nterstitial atoms under that tensile stress field that causes the formation of c opper clusters.
2005, 54 (2): 832-836.
doi: 10.7498/aps.54.832
Abstract +
The resistance and magnetic susceptibility of Sm1-xGdxAl2 with x=00098, 0019 and 003 have been studied at low temperatures. Spin moments and orbital moments couple antiparallelly in this material. The compensat ion temperature at which the spin moments are equal to orbital ones is observed, and it decreases with increasing x. The spin_orbit flip has been found in a strong field.
2005, 54 (2): 837-841.
doi: 10.7498/aps.54.837
Abstract +
The polytetra_fluoroethylene (PTFE) substrates were implanted with 160 kev N ions to a dose range between 1×１0１4 and １×１017 ions/cm2 at di fferent temperatures. The treated samples were examined by visible (5145 nm) a nd Fourier transform infrared (1064 nm) Raman spectroscopy as well as by scannin g electron microscopy. Ion implantation on PTFE in the low dose range leads to e nhancement of crystallinity of PTFE. In the intermediate dose range, sputter los s effects are dominant and the roughness of the surface increases. At higher dos es, the microstructure strongly evolves and double CC bonds are created. In addi tion, the etching yield and the changing extent of the surface microstructure ar e enhanced by the temperature of PTFE substrate.
2005, 54 (2): 842-847.
doi: 10.7498/aps.54.842
Abstract +
Transparent and conductive oxides CdIn2O4 (CIO) thin films were prepared by RF reactive sputtering from a CdIn alloy target in Ar+O2 atmosphere. By the analysis and measurements of transmittance spectra and Hall_effect of different samples prepared at different substrate temperatures and post_deposition annealing in an Ar gas flow, it was found that the carrier density increases with the d ecrease of substrate temperature, but the absorption edge shows an abrupt change from a blue_shift to a red_shift. Theoretically, the paper formulated the effec t on band structure due to higher density of point defects, it embodies the band _tailing, Burstein_Moss (B_M) shift and band_gap narrowing. In addition,density of ionized impurity substrate temperature induced will affect the carrier mobili ty.The hole density impurity_induced will influences the magnitude of optical ba nd_gap and transmittance of light. Since extrapolation method does not fit degen erate materials, a more accurate method of obtaining band_gap is the method of c urve fitting.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2005, 54 (2): 848-856.
doi: 10.7498/aps.54.848
Abstract +
This paper have studied the structures、microstrain distributions、and optical properties of self-assembled quantum wires Ga1-xInxAs made of sho rt-period superlattices with strain induced lateral ordering. The research has t aken into account of valence-band anisotropy, band mixing and effects due to mic rostrain distributions at the atomistic level. The results show that the selfa ssembled QWRs have favorable optical properties for application in infrared dete ction with normal incidence. The wavelength for subband transitions ranges from 10 to 20μm with the length of QWR period varying from 15 to 30nm. The wavelengt h for inter-band absorption is in the midIR range.
2005, 54 (2): 857-862.
doi: 10.7498/aps.54.857
Abstract +
Based on the generalized gradient approximation (GGA), the totalenergy, overlap populations and valence charges in the case of Ti atoms moving along c axi s in cubic and tetragonal phases were calculated by using ultrasoft pseudopotent ials (USP) plane wave method. It was demonstrated that the energy of tetragonal BaTiO3 was the lowest when Ti atoms move along the c axis by up to 0012n m, and the spontaneous polarization was 0261C/m2 , which was consistent with experimental results. Moreover, it was also confirmed that the ferroelectric st ability of BaTiO3 could be attributed to the orbital hybridization of 2p orbit of oxygen atom and 3d orbit of Ti atom.
2005, 54 (2): 863-867.
doi: 10.7498/aps.54.863
Abstract +
The local structure geometry around a lead vacancy V2-Pb in PbWO 4 is optimized using a planewave pseudopotential formulation within the fr amework of local density approximation (LDA), with generalized gradient correcti on in the form of Perdew_Wang_91 The results of the lattice relaxation decreas e the electrical negativity on V2-Pb site and increase the elect rical positivity on O2- site near by the V2-Pb. All of the electronic structures around V2-Pb in PWO crystal are studied i n the molecular_cluster model with the framework of the fully relativistic self_ consistent Direc_Slater theory by using a numerically discrete variational (DV_X α) method. By analyzing the electronic structures, we can reasonably believe th at once V2-Pb is formed in PWO crystal, O2- turns to be pr ior to trap holes to compensate the electrical negativity of V2-Pb . Pb2+ may never be the holetrapper compensating V2-Pb , and Pb3+ and Pb4+ in PWO crystal may not actually exist. The possi ble defect micromodel caused by V2-Pb in the asgrown PWO cry stal is that each V2-Pb creates a V＋KV-F aggr egate color center.
2005, 54 (2): 868-874.
doi: 10.7498/aps.54.868
Abstract +
By using the plane_wave ultrasoft pseudopotential method, the geometric parameters, electric and optical properties of Rb2TeW3O12 are investigated. The equilibrium lattice constants are in good agreement with experimental data. The electric structures reveal that Rb2TeW3O12 is a direct wide_band semiconductor and the band gap is 223eV; W 5d and O 2p states form a strong W— O covalent bond. Optical properties have been studied and we have presented the dielectronic functions ε1 and ε2. Static dielectric constant ε 0=529 have been gained.
2005, 54 (2): 875-879.
doi: 10.7498/aps.54.875
Abstract +
The model of 1/2［110］ edge dislocation in austenite phase was set up with comp uter programming. The environmentsensitive embedding energy (ESE) of C, N and alloy elements in grains or in the area of edge dislocation was calculated by us ing recursion method. The enrichment and interaction of C, N and alloy elements in the area of dislocation were discussed. Calculation results show that: discre te light impurities C and N tend to aggregate in the dislocation area, forming C aldwell air mass above the edge dislocation; the alloy element is liable to dist ribute in perfect austenite grains. Ti, V, Nb and Cr, which are strong or middli ng strong elements for carbide formation, are easy to aggregate in the edge disl ocation area. They can also form the Caldwell air mass above the edge dislocatio n like C or N. But Ni, which is non_carbide formation element, aggregates below the dislocation line or distributed in the perfect grains. The light impurity ca n enforce the aggregation of strong carbide forming elements in the edge disloca tion area. When the temperature is decreased, and when the concentration of C, N and alloy elements reach the high limit of concentration, the C, N compound of alloying elements will precipitate from the matrix in the edge dislocation area of austenite in the steel. These compounds can act as heterogeneous nuclei of au stenite phase in the course of recrystallization, leading to the refinement of a ustenite grains.
2005, 54 (2): 880-885.
doi: 10.7498/aps.54.880
Abstract +
The optical emission spectra of atomic hydrogen, atomic carbon and radical CH in electron assisted chemical vapor deposition (EACVD) were studied by using the Monte Carlo simulation when CH4/H2 gas mixture was used as the input gases. Effects of the experimental parameters on emission spectra and synthesis of di amond films were investigated. The results obtained suggested that the CH radica ls should be considered as a precursor species for diamond deposition but atomic carbon C is not. The diamond growth rate may be enhanced by the substrate bias due to the changes of atomic hydrogen concentration and the increase of mean ele ctron temperature. A method of determining the mean temperature of electron was gained by using atomic hydrogen emission line, and the optimum experimental cond ition for diamond deposition was also obtained. These results are of great impor tance for depositing high_quality diamond films by controlling the conditions of technology efficiently.
2005, 54 (2): 886-891.
doi: 10.7498/aps.54.886
Abstract +
The variation of the electronic energy in a columnar nanometer system with the i ncrease of radius is established, and the HgS/CdS/HgS nanometer system is used to discuss the influence of the layer_to_layer interaction energy on the electr onic energy spectrum of electrons. Some important results indicate that the ene rgy of the electronic energy increases with the increase of the potential barrie r width and the wave vector, while the potential well width and the layer_to_la yer interaction energy makes the electronic energy larger, but it doesn't effec t the variation of electronic energy with the potential well width, potential ba rrier or the wave vector.
2005, 54 (2): 892-896.
doi: 10.7498/aps.54.892
Abstract +
Using decamethylcyclopentasioxane (［Si(CH3)2O］5 as liquid precursor, SiCOH films, which have low dielectric constant (low k), good insulating ability and thermal stability, were prepared by electron cyclotron resonance chemical vapor deposition (ECR_CVD). The FTIR spectra of the films were measured to find the difference of bond structures between SiCOH films and DM5 source. It was verified that the Si—O—Si cyclic structure was retained in SiCOH films,while _CH3 radicals were lost during the deposition. The dielectric con stant decreased from 385 to 285 after the film was annealed in 400℃. With t he analysis of the bond structure of the film as deposited and annealed, we can infer that the increased content of cage structure comprised of Si—O—Si bond w ith bigger bond angle may be the reason for decreased dielectric constant.
2005, 54 (2): 897-901.
doi: 10.7498/aps.54.897
Abstract +
Based on the improved approximation of modified triangular potential well, a phy sical_based model of MOSFETs threshold voltage is presented, as well as its anal ytical formulation. The new model takes quantum effects into account for future generation MOS devices and integration circuits. The calculated results by using the new model agree with the simulation results very well.
2005, 54 (2): 902-906.
doi: 10.7498/aps.54.902
Abstract +
The magnetic transition behaviors of (Pr1-yNdy)2/3Sr 1/3MnO3(y=2/8,4/8,6/8) polycrystalline samples under superposed ma gnetic fields (i.e., the superposed ac and dc magnetic field) were systematicall y studied at temperatures ranging from 42 to 300K. The results showed that the magnetization increases with the increase of magnetic field, and the real part of the ac susceptibility decreases as the superposed dc magnetic field increases . Under the superposed magnetic field, a characteristic sharp peak of the real p art of the susceptibility appears near the magnetic transition temperature (Curi e temperature). For the (Pr1-yNdy)2/3Sr1/3MnO 3 system, as the Nd content increases, the peak temperature of the relative variation of the real part of susceptibility (Eχ′=Δχ′/χ′ dc) decreases, in consistent with that of the magnetoresistivity of this sys tem. The magnetic transition behaviors under superposed magnetic fields for the manganite systems are discussed.
2005, 54 (2): 907-911.
doi: 10.7498/aps.54.907
Abstract +
Polycrystalline powders of the family of compounds Sr2Fe1-xAl xMoO6 (x=0, 005, 010, 015, 030) were prepared according to the standard solid_state reaction . XRD patterns and SEM images show that the structure and the grain size of these compounds were not changed and no imp urity was observed by doping with Al in Sr2FeMoO6. In the cationic ordered s egregation, a large ferrimagnetic patch can be separated into some smaller ones by the Al doping. So the chain of the ferrimagnetic exchange path will be short ened and the strength of exchange will be weakened. Therefore, their moments bec ome more sensitive to external field. Furthermore, when the Al ion replaces the Fe ion in the disordered segregation, the antiferromagnetic coupling becomes wea ker. As a result, the low_field magnetoresistance is enhanced. But the smaller f errimagnetic segregates become more sensitive to thermal agitation at high temp eratures. The weakness of the Al_doped SFMO lies in its stronger temperature dep endence of the saturated moments and the low_field magnetoresistance.
2005, 54 (2): 912-919.
doi: 10.7498/aps.54.912
Abstract +
In this paper, the M_T curves, ESR, Infrared and Raman spectra, ρ_T cu rves and MR_T curves of La067-xSmxSr033MnO 3 (x=000, 010, 020, 030) are studied. The experimental results ind icate that with increasing Sm content, the compound undergoes a transition from long_range ferromagnetic order to the cluster_spin glass state, and further to a ntiferromagnetic order. The variation in magnetic structure and extra magnetic c oupling caused by Sm doping lead to colossal magnetoresistance effect.
2005, 54 (2): 920-929.
doi: 10.7498/aps.54.920
Abstract +
The M_T curves, M_H curves, ρＴ curves and MR_T curves of La0.7-xDyxSr0.3MnO3 (x=000，030，040，050，060 and 070) are studied. Experimental results indicate that with increasing do ping concentration of Dy, the system changes from long_range ferromagnetic order to cluster_spin glass state, then to antiferromagnetic state and to subferromag netic state. For x=03, there appears a peak on the M_T curve near T N,however, it disappears at x=04. For x=05, and zero field cooli ng(ZFC) the curve shows a valley, and then a peak at TN; after the 001 T field cooling process, the initial value of M is negative at low temperatur es. For x=060 and 070, their ZFC and FC M_T curves are both similar to the ZFC one of x=050, and the transport properties at heavy doping beco me abnormal under a magnetic background. The peculiar phenomena shown above can be interpreted in terms of the Nel's double_lattice model combined with the re sultsof M_H hysteresis at the characteristic temperatures.
2005, 54 (2): 930-934.
doi: 10.7498/aps.54.930
Abstract +
Arrays of NiFe2O4 nanowires were prepared by using porous anodic al uminum oxide(AAO) membrane as the template. For the preparation of the ferrite n anowires, Ni_Fe alloy nanowires were electrodeposited into the pores of the AAO membranes. The atomic ratio is about Ni∶Fe=1∶2 which can be detected by engerg y dispersive spectroscopy. X-ray diffraction study showed the pure phase of NiFe 2O4 after anodization. SEM and TEM studies showed the diameters of t he pores and the nanowires are all about 70nm. The vibrating sample magnetometer studies of the nanowire arrays showed the anisotropic magnetic properties befor e and after anodization. Coercivity and squareness ratio have been improved appa rently in the NiFe2O4 nanowires arrays.
2005, 54 (2): 935-938.
doi: 10.7498/aps.54.935
Abstract +
Ultrahigh piezoelectric response along easy cleavage plane in BaTiO3 singl e_crystal was found. An extremely high value of piezoelectric coefficient d 33 value over 2000 pC/N was obtained after being poled perpendicular to th is plane of BaTiO3 crystal, which is more than 20 times higher than those poled along spontaneous polarization direction 〈001〉 (d33〈001〉=87p C/N). A large strain of 06% was obtained at a very low electric field. The res ults may generate a wide range of lead_free materials for the piezoelectric tran sducer application.
2005, 54 (2): 939-943.
doi: 10.7498/aps.54.939
Abstract +
The frequency and temperature dependence of the hysteresis loops in Pb［(Zr0 52Ti048)095(Mn1/3Nb2/3)005］O3 (PM nN_PZT) ceramics have been investigated. It has been demonstrated that the polar ization_field hysteresis curves show “pinched" shapes instead of the normal squ are_like P_E loops when tested at room temperature or higher frequency. While at 200℃ or lower frequency, normal square_like loops are observed. In the meantim e, important ferroelectric features such as coercive field, polarization and int ernal bias field are strongly frequency or temperature dependent. High increase of the remnant polarization (Pr) reveals that there may be defect dipo les that induce the unsaturated hysteresis loop. The close relations between the P_E loops and the applied frequencies or temperatures indicate that there exist s a typical relaxation time associated with reorientation of the defect dipoles.
2005, 54 (2): 944-948.
doi: 10.7498/aps.54.944
Abstract +
The effect of Al substitution for Fe on the spin reorientation and Mssbauer spectra of a series of Tb03Dy07(Fe1-xAlx)195 alloys (x=005，01，015，020，025，030，035) at room temperature and 77K has been investigated systematically. The results indicate that the easy magnetization direction in the {100} plane deviates slightly from the main axis of symmetry, namely spin rerioentation. A small amount of non_magnetic phase exists for x=015, and the alloys become paramagnetism when x>015 at room temperture, but at 77K the alloys still remain to be magnetic phase even at x=02. At room temperature and 77K, the hyperfine field decreases and the isomer shift increases with increasing concentration of Al, and the quaduple splitting QS shows weak concentration dependence.
2005, 54 (2): 949-954.
doi: 10.7498/aps.54.949
Abstract +
Based on the characteristic of ferroelectric microstructure, a crystal cell of ferroelectric is regarded as a dipole. Analysis of the switching property of di pole in the electric filed is made. According to the statistic principle, differ ent distribution functions are used to fit the probability of dipole switching. A model based on hysteresis loop is developed. Experimental data on PZT show go od agreement with the model for various loops, and the model is easily linked to simulative software of circuit for either memory or analog design application.
2005, 54 (2): 955-960.
doi: 10.7498/aps.54.955
Abstract +
The novel optical properties of wave propagation and the special feature of phot on geometric phases inside a noncoplanarly curved fiber made of biaxially anisot ropic left_handed media are considered in this paper. In general, the photon geo metric phases is inevitably dependent on the solid angle subtended by the curve along which the photon moves, which presents the topological and global property of time evolution of photon wavefunctions. It is, however, shown that inside a biaxially anisotropic left_handed fiber the photon geometric phases will be inde pendent of the cone angle, since the contributions of negative and positive refr active indices to the geometric phases of circularly polarized photons have been cancelled each other. In addition, we discuss briefly the properties of the qua ntum_vacuum geometric phases resulting from the quantum vacuum fluctuation, and the probability of the detection of such a vacuum effect in experiments.
2005, 54 (2): 961-966.
doi: 10.7498/aps.54.961
Abstract +
Quantitative analysis of Raman spectra of vitreous or molten silicate is always one of the key subjects in some fields, e.g. materials science, geological physi cs, etc. But there are many difficulties with this analysis, one of which is the determination of Raman scattering coefficient. Not long ago, we developed a new method for the calculation of Raman spectrum of amorphous silicate. Essentiall y, this method combines the molecular dynamics simulation with wilson's GF matri x method, electro_optical parameter method and bond polarizability model. With t his theoretical method, we have studied the Raman scattering coefficients of sym metrical stretching modes of Qi in sodium silicate melts, and concluded th at these coefficients are independent of composition. Meanwhile, the five values of the coefficients are also given as follows: S0=１, S1=0514, S2=0 242, S3=0090 and S4=0015 In order to apply these quantities to experiments, the Raman spectrum of sodium disilicate melt has been measured and its high_frequency envelope has been deconvolved into three Gaussian bands. Fina lly, the molar fractions of Qi were achieved by dividing the area fraction s of the three Gaussian bands by corresponding scattering coefficients. Addition ally, combining the results of theoretical calculation and quantitative analysis of experimental spectra, we found that the intensities of anti_symmetrical stre tching modes of Q0 and Q2 in sodium silicate melts are so strong tha t they cannot be neglected in the deconvolution process.
2005, 54 (2): 967-971.
doi: 10.7498/aps.54.967
Abstract +
Based on the rate equations of a two_level system, the analytical solutions of r elaxation of carrier populations with spin_up and spin_down polarization are obt ained under the condition of incomplete initial spin polarization. In the small signal regime, the saturated absorption_change expression of right_ and left_cir cularly polarized probe beam is given. The parameter, initial degree of spin pol arization of electron population, appears in the expression. Therefore, the init ial degree of spin polarization of electron population, which is a very importan t key parameter in the transport of spin polarization, can be extracted by fitti ng the expression to the saturated absorption trace obtained experimentally. Fin ally, the initial degree of spin polarization of photo_injected electron populat ion and its relaxation time constant in GaAs/AlGaAs multiple quantum wells are a cquired in experiments.
2005, 54 (2): 972-976.
doi: 10.7498/aps.54.972
Abstract +
We investigate the oxidation behavior of Si1-xGex alloys ( x=0005，002，005，015 and 025). A new ellipsometric method is used f or the generating and measuring Ge nanostructures in oxidation of SiGe alloys. The fundamental optical constants of Ge nanolayers in the sample were determined by ellipsometry. The thickness and origin of the Ge bi_nanolayer were found. A new peak in photoluminescence PL spectra was discovered, which is related to the Ge bi_nanolayer (thickness: 08—14nm). Some suitable model and calculating formula can be provided with the UHFR method and quantum confinement analysis to interprete the PL spectrum and the nanostructure mechanism in the oxide.
2005, 54 (2): 977-981.
doi: 10.7498/aps.54.977
Abstract +
Based on the original design of T.G.Leighton's conical bubble U_tube，an improve d apparatus is set up. The light pulses and spectra of air bubbles in water are detected. Results show that the width of a light pulse ranges from a few of hun dred picoseconds to a few nanoseconds. The vibrational spectra of water molecule s in the near_infrared have been obtained，and its intensity increases toward th e infrared. The spectra of conical bubble in NaCl solution is also detected.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2005, 54 (2): 982-986.
doi: 10.7498/aps.54.982
Abstract +
Co:BaTiO3 nano_composite thin films on single_crystal magnesia(100) were successfully fabricated by pulsed laser deposition. The morphology and microstructure of the thin films were investigated via atomic force microscope, x_ray diffractometer and Raman spectroscopy. The results show that the thin films consisted o f a highly c_axis oriented tetragonal phase. The surfaces of the thin films were uniform, compact and of atomic smoothness (RMS=015nm). The co particles, of monodisperse distribution, were found to be well dispersed in the matrix Co: BaTiO3. With increasing Co grain size, the intensities of Raman peaks were wea kened and their width broadened.
2005, 54 (2): 987-992.
doi: 10.7498/aps.54.987
Abstract +
Based on the spectral representation theory and the perturbative expansion metho d, the general expressions for effective nonlinear responses (χe a nd ηe) are derived for any complicated micro structures. The higher_orde r nonlinear response of two_component composite is studied by using the effectiv e medium approximation. The effective dielectric constant of the composite is gi ven by ε～e=εe+χe|E0|2+ηe|E0|4. The effe ctive cubic order nonlinear response χe and the higher_order response ηe for the whole volume fraction p of the nonlinear component ar e investigated and the general expressions of χeand ηeare g iven in this paper. We also perform numerical simulations for χe and ηe in the case of complex dielectric constant of the nonlinear co mponent. The effect of the higher order nonlinear responses on the effective di electric constant of the composite is theoretically studied.
