Influence of Channel Power and Pumping Configuration on the Gain Profile of Distributed Raman Fibre Amplifier

The influence of channel power and pumping configuration on the gain profile of a distributed Raman fibre amplifier has been experimentally measured.The experimental results show that the influence is significant and should be considered during the gain flatness optimization of the distributed Raman fibre amplifier.     

Optimal Density Profile of the Plasma Layer Shielded by a Conducting Surface for the Absorption of Electromagnetic Waves

Based on the Born approximation, we reduce the approximate analysis solution to the normal and oblique incident electromagnetic wave scattering from the weakly ionized plasma layer shielded by a conducting surface. The solution is closely related to the density profile of the plasma layer. Employing the self-consistent base function, we yield the optimal density profile for the nonuniform plasma layer with the frequencies of incident electromagnetic waves ranging from 4-10 GHz. Numerical studies illustrate the optimal density profile can “survive” wide ranges of the plasma parameters. Different from the validity condition for the Wenzell-Kramers-Brillouin-Jeffreys(WKBJ) approximation, the Born approximation is feasible even if the scale length is smaller than the wavelength.Therefore, the Born approximation is universal against the scattering problem from the weakly ionized plasma.     

Effective Medium Model for Refractive Indices of Thin Films with Oblique Columnar Structure

The refractive indices of thin films, containing dielectric and voids in an oblique columnar structure, are modelled in the quasi-static limit. The dielectric function is shown to be strongly dependent on the angle of incidence and on the columnar orientation for p-polarized light. This model is applied to model ZnS thin films with oblique columnar structures and the computed results have been given.     

Gain Saturation Effects of a Flowing Chemical Oxygen-Iodine Laser

A new oxygen-iodine medium gain model is developed to include pumping and deactivation of the upper laserlevels of the iodine atoms, hyperfine and translation relaxation, as well as the flowing effect. The rate equationsfor gain of a supersonic flowing cw oxygen-iodine laser (COIL) are described when the medium is stimulated bya single-mode field. The general solution of the self-consistency integral equation is obtained. The result showsthat the saturation behaviour in low pressure of the COIL differs from both the inhomogeneous and homogeneousbroadening, and exhibits an ‘anomalous‘ saturation phenomenon.     

First-Principle-Based Calculations of the Hugoniot of Cu

The equation of state of face-centred-cubic (fcc) copper crystals at pressures up to 500 GPa and relative volume to 0.55 have been evaluated by using the full-potential linear muffin-tin orbital (FPLMTO) total-energy method combining with a mean-field model of the vibrational partition function. The mean-field is constructed from the sum of all the pair potentials between the reference atom and the others of the system. The calculated properties are in good agreement with the available shock-wave experimental measurements.     

Mathematical structure of the three-dimensional（3D） Ising model

An overview of the mathematical structure of the three-dimensional(3D) Ising model is given from the points of view of topology,algebra,and geometry.By analyzing the relationships among transfer matrices of the 3D Ising model,Reidemeister moves in the knot theory,Yang-Baxter and tetrahedron equations,the following facts are illustrated for the 3D Ising model.1) The complex quaternion basis constructed for the 3D Ising model naturally represents the rotation in a(3+1)-dimensional space-time as a relativistic quantum statistical mechanics model,which is consistent with the 4-fold integrand of the partition function obtained by taking the time average.2) A unitary transformation with a matrix that is a spin representation in 2 n·l·o-space corresponds to a rotation in 2n·l·o-space,which serves to smooth all the crossings in the transfer matrices and contributes the non-trivial topological part of the partition function of the 3D Ising model.3) A tetrahedron relationship would ensure the commutativity of the transfer matrices and the integrability of the 3D Ising model,and its existence is guaranteed by the Jordan algebra and the Jordan-von Neumann-Wigner procedures.4) The unitary transformation for smoothing the crossings in the transfer matrices changes the wave functions by complex phases φx,φy,and φz.The relationship with quantum field and gauge theories and the physical significance of the weight factors are discussed in detail.The conjectured exact solution is compared with numerical results,and the singularities at/near infinite temperature are inspected.The analyticity in β=1/(kBT) of both the hard-core and the Ising models has been proved only for β0,not for β=0.Thus the high-temperature series cannot serve as a standard for judging a putative exact solution of the 3D Ising model.     

Calculation of the Spatio-Temporal Dynamics of Q-switched Yb^3＋：YAG Laser with an Unstable Cavity and a Super-Gaussian Mirror

A numerical simulation used to compute the spatio-temporal dynamics of pulse formation of diode-pumped Q- switched Yb： YA G laser is carried out. The model takes the laser amplification and gain saturation, the properties of the laser cavity, and the diffractive effects of the laser disc into account. The numerical calculation is performed for a confocal positive-branch unstable resonator with a super Gaussian coupling mirror. The simulation results show that the laser pulse starts from a Gaussian intensity distribution and becomes rapidly non-Gaussian. The corresponding beam quality M^2 factor is seen to vary approximately from 1.5 at the beginning of the formation of pulse to more than 10 in the tail of the pulse, with a value of 11.6 at the peak of the pulse.     

Retrieval of C_n~2 profile from differential column image motion lidar using the regularization method

We develop a regularization-based algorithm for reconstructing the C_n~2 profile using the profile of Fried's transverse coherent length(r_0) of differential column image motion(DCIM) lidar. This algorithm consists of fitting the set of measured data to a spline function and a two-stage inversion method based on regularized least squares QR-factorization(LSQR) in combination with an adaptive selection method. The performance of this algorithm is analyzed by a simulated profile generated from the HV5∕7model and experimental DCIM lidar data. Both the simulation and experiment support the presented approach. It is shown that the algorithm can be applied to estimate a reliable C_n~2 profile from DCIM lidar.     

Dielectric Properties of GaN in THz Frequencies

The complex refractive indices and the dielectric function of GaN for frequencies ranging from 0.25 to 1.22THz are obtained using THz time-domain spectroscopy. The real part of the dielectric function first decreases from 0.25 to 0.42THz and then oscillates from 0.42 to 1.22THz, whereas the imaginary part of the dielectric function is oscillating within the whole range of frequency. The simple Drude model is extended to take into account the effect of defects on the dielectric function. The extended model is in agreement with the experimental data.     

Calculation of Free Energy of the Integrable Landau—Lifshitz model

The generalized Bethe-ansatz method of thermodynamic analysis of integrable systems was employed to compute the free energy of a classical integrable model,i.e.the Landau-Lifshitz model.Using the action-angle variables of the model and by imposing a periodic boundary condition.we derive a phase-shifted density of states for the excitations of the system.The free energy,in the thermodynamic limit,can be expressed analytic in terms of two coupled nonlinear integral equations of the finie temperature excited energy for effective phonons and kinks (antikinks).we solve these equations iteratively for a special case that the model is in the limit of anisotropic strong yz coupling.     

A Geometry Model for Tortuosity of Flow Path in Porous Media

A simple geometry model for tortuosity of flow path in porous media is proposed based on the assumption that some particles in a porous medium are unrestrictedly overlapped and the others are not. The proposed model is expressed as a function of porosity and there is no empirical constant in this model. The model predictions are compared with those from available correlations obtained numerically and experimentally, both of which are in agreement with each other. The present model can also give the tortuosity with a good approximation near the percolation threshold. The validity of the present tortuosity model is thus verified.     

Analytical formula of free electron laser exponential gain for a non-resonant electron beam

The free electron laser(FEL) gain formulas for a non-resonant case are studied, and some new rigorous analytical formulas are given explicitly. For the mono-energetic and non-resonant electron beam, the exact expression of the solution of the FEL characteristic cubic equation is obtained with a form much more simple than that in the literatures, and the gain length as the function of the detuning parameter is explicitly given. Then the gain for different detuning parameters and from low to high can be easily calculated. A simplified approximation formula is also given for the exponential gain calculation in the non-resonant case. For the case of the electron beam with an energy spread, the solution of the characteristic cubic equation is given explicitly for rectangular energy distribution and Lorentz distribution, respectively. Moreover the explicit expression also can be used for the solution of the characteristic cubic equation including the impact of the space charge. The transition from the low gain to the high gain is analyzed. The variations of the gain bandwidth and of the detuning parameter for the maximum gain are demonstrated. The applicable ranges of the small signal gain formula and the exponential gain formula are analyzed.     

Geologic investigation and mapping of the Sinus Iridum quadrangle from Clementine,SELENE, and Chang’e-1 data

The objectives of lunar satellite remote sensing are to study lunar surface characteristics, inner structure, and its evolution history. The contents of TiO 2 and FeO are assessed from Clementine UV/VIS data for Sinus Iridum. The geologic stratigraphic units and crates are interpreted visually based on SELENE Terrain Camera (TC) images and the spatial resolution of which is up to 10 m. And the geologic ages of different stratigraphic units are calculated by the crater size-frequency distributions measurements. The gravity anomaly is generated from SELENE gravity model (SGM90d) to show its difference from Mare Imbrium. Furthermore, the thickness of lunar regolith is also derived from microwave radiometer data of Chang’e-1 satellite. Integrating these results, it shows that the Sinus Iridum is different from the Mare Imbrium in inner structure and surface sedimentation. And its history of subsidence, deposition, volcanism, and impact is described. It makes sense to the future soft-landing and sampling at potential Sinus Iridum by remote sensing geologic analysis.     

Fermi-Dirac Statistics of Complex Networks

We investigate phenomena of decline of complex networks by employing and analysing an illness model. Itsintr insic relation with the Fermi distribution is shown and a mapping to Fermi gas is established. The results of numerical simulations are obtained in two ways. We also compare the model with other models, including the dual relationship with the fitness model, and its difference from the Cayley tree model.     

Investigation on the temperature compensating model for ring laser gyroscope

Thermal effects impose the greatest limit on the precision of a ring laser gyro (RLG). Selections of temperature sensing points were comparatively discussed based on large numbers of experimental data to improve its precision, and the optimum combination was selected to establish a practical compensating model. The model is applied to new experimental data under the given and varied temperatures. Results show that the bias trend changing with the temperature is basically eliminated and the bias stability is enhanced significantly.     

A Solution of the DGLAP Equation for Gluon Distribution as a Function of F2 and dF2/dlnQ^2 at Low x： the Next-to-Leading Order Analysis

We obtain a solution of the DGLAP equation to extract the gluon distribution function from the deep inelastic structure function F2 and its derivative with respect to In Q^2 at low x in the next-to-leading order of perturbation theory. The values of the gluon distribution are found in the range 10^- 4 ≤ x ≤ 10^-2 at Q^2 = 20 GeV^2, We test its validity by comparing it with that of Glueck, Reya and Vogt. The detailed analysis is given for the HERA data.     

A Novel Method for Multi-Pumped Fibre Raman Amplifier Gain Adjustment

A novel method for gain adjustment of multi-pumped fibre Raman amplifiers is proposed and numerically demonstrated. The method uses the areas under the curves of the pump power evolution along the gain fibre and the Newton-Raphson method to find an appropriate power combination of the pumps to realize the desired gain profile. Compared with the previously proposed methods, our method has two advantages: first, it can maintain the gain profile while changing the gain magnitude to the desired value; second, it is independent of the actual pumping scheme of the amplifier, i.e. it can be used for fibre Raman amplifiers with all kinds of pumping schemes including co-, counter-, or hi-directional pumping. Numerical simulations are provided to verify the proposed method and to demonstrate its effectiveness.     

The laser-intensity dependence of the photoassociation spectrum of the ultracold Cs2（6S1/2 ＋ 6P1/2） 0＋ long-range molecular state

The high-resolution photoassociation spectrum of the ultracold cesium molecular 0＋ state below the 6S1/2 ＋ 6PI/2 limit is presented in this paper. The saturation of the photoassociation scattering probability is observed from the depen dence of the trap-loss probability on the photoassociation laser intensity. The corresponding resonant line width is also demonstrated to increase linearly with increasing photoassociation laser intensity. Our experimental data have good con sistency with the theoretical saturation model of Bohn and Julienne [Bohn J L and Julienne P S 1999 Phys. Rev. A 60 1].     

Neutralization process of Xe^q＋ ion grazing on Al（111） surface

A code has been developed to simulate the neutralization and grazing process of slow highly charged ion Xe^q＋ on Al（111） surface under the classical-over-the-barrier model. The image energy gain of Xeq＋ ions are calculated and compared with experiment data. The simulation results of image energy gain are in good agreement with the experiment data. Meanwhile, in the present work, the reflection coefficient of incident Xe^q＋ on Al（111） surface as a function of the incidence angle, energy and charge state is also studied.     

Refractivity estimations from an angle-of-arrival spectrum

This paper addresses the probability of atmospheric refractivity estimation by using field measurements at an array of radio receivers in terms of angle-of-arrival spectrum.Angle-of-arrival spectrum information is simulated by the ray optics model and refractivity is expressed in the presence of an ideal tri-linear profile.The estimation of the refractivity is organized as an optimization problem and a genetic algorithm is used to search for the optimal solution from various trial refractivity profiles.Theoretical analysis demonstrates the feasibility of this method to retrieve the refractivity parameters.Simulation results indicate that this approach has a fair anti-noise ability and its accuracy performance is mainly dependent on the antenna aperture size and its positions.