Fiber optical parametric oscillator based on photonic crystal fiber pumped with all-normal-dispersion mode-locked Yb:fiber laser

We demonstrate a cost effective, linearly tunable fiber optical parametric oscillator based on a home-made photonic crystal fiber pumped with a mode-locked ytterbium-doped fiber laser, providing linely tuning ranges from 1018 nm to 1038 nm for the idler wavelength and from 1097 nm to 1117 nm for the signal wavelength by tuning the pump wavelength and the cavity length. In order to obtain the desired fiber with a zero dispersion wavelength around 1060 rim, eight sam- ples of photonic crystal fibers with gradually changed structural parameters are fabricated for the reason that it is difficult to accurately customize the structural dimensions during fabrication. We verify the usability of the fabricated fiber experimen- tally via optical parametric generation and conclude a successful procedure of design, fabirication, and verification. A seed source of home-made all-normal-dispersion mode-locked ytterbium-doped fiber laser with 38.57 ps pulsewidth around the 1064 nm wavelength is used to pump the fiber optical parametric oscillator. The wide picosecond pulse pump laser enables a larger walk-off tolerance between the pump light and the oscillating light as well as a longer photonic crystal fiber of 20 m superior to the femtosecond pulse lasers, resulting in a larger parametric amplification and a lower threshold pump power of 15.8 dBm of the fiber optical parametric oscillator.     

Reflective graphene oxide absorber for passively mode-locked laser operating at nearly 1μm

A low cost and simply fabricated reflective graphene oxide is successfully made. By using this absorber, as well as an end reflector, we obtain a passively mode-locked Yb:LuYSiO5 laser operating at nearly 1 μm. When the pump power is increased up to 5.73 W, stable mode locking is achieved. The central wavelength of the laser spectrum is 1043.2 nm with a pulse duration of 5.0 ps. When the pump power reaches 8.16 W, dual-wavelength mode locking laser pulses at 1036.3 nm and 1043.5 nm are simultaneously detected.     

Systematical analysis of mode-locked fiber lasers using single-walled carbon nanotube saturable absorbers

The output characteristics of the Er-doped mode-locked fiber laser using a single-walled carbon nanotube saturable absorber are investigated theoretically with a nonlinear Schrtidinger equation and a saturable absorption equation using realistic parameters. Stable self-starting mode-locking pulses are achieved under net normal, net zero, and net anomalous cavity group velocity dispersion （GVD） respectively. A spectrum with a flat top is obtained from the net normal cavity GVD laser while a spectrum with Kelly side-bands is obtained from the net anomalous cavity GVD laser. The characteristics of the pulse duration changing with cavity GVD and modulation depth of the single-walled carbon nanotubes are discussed. The characteristics of the mode-locking pulses from net normal, net zero, and net anomalous cavity GVD mode-locked fiber lasers are compared. These systematical results are useful for designing mode-locked fiber lasers with saturable absorbers made by different kinds of carbon nano-materials.     

Effect of Spatial Dimension and External Potential on Joule-Thomson Coefficients of Ideal Bose Gases

Based on the form of the n-dimensional generic power-law potential, the state equation and the heat capacity, the analytical expressions of the Joule-Thomson coefficient （3TC） for an ideal Bose gas are derived in n-dimensional potential. The effect of the spatial dimension and the external potential on the JTC are discussed, respectively. These results show that： （i） For the free ideal Bose gas, when n/s ≤ 2 （n is the spatial dimension, s is the momentum index in the relation between the energy and the momentum）, and T → Tc （Tc is the critical temperature）, the JTC can obviously improve by means of changing the throttle valve＇s shape and decreasing the spatial dimension of gases. （ii） For the inhomogeneous external potential, the discriminant △= [1 - y∏^ni=1（kT/εi）^1/tiГ（1/ti＋1）] （k is the Boltzmann Constant, T is the thermodynamic temperature, ε is the external field＇s energy）, is obtained. The potential makes the JTC increase when △ 〉 0, on the contrary, it makes the JTC decrease when A 〈△. （iii） In the homogenous strong external potential, the JTC gets the maximum on the condition of kTεi〈〈1.     

Experiment of constraining symmetry energy at supra-saturation density with π^-/π^＋ at HIRFL-CSR

The possibility of the experiment for constraining the symmetry energy Esym（ρ） at supra-densities via π^-/π^＋ probe on the external target experiment of phase I （ ETE（I） ） with part coverage at forward angle at HIRFL-CSR is studied for the first time by using the isospin and momentum dependent hadronic transport model IBUU04. Based on the transport simulation with Au＋Au collisions at 400 MeV/u, it is found that the differential π^-/π^＋ ratios are more sensitive to Esym（ρ） at forward angles in laboratory reference, compared with the total yield ratio widely proposed. The insufficient coverage at lower transverse momentum maintains the sensitivity of the dependence of π^-/π^＋ ratio on the Esym（ρ） at high density, indicating that the ETF （I） under construction in Lanzhou provides the possibility of performing the experiment for probing the asymmetric nuclear equation of state.     

An Extended Extrinsic Mechanism for Anomalous Hall Effect

The extrinsic mechanism for anomalous Hall effect in ferromagnets is extended to include the contributions both from spin-orbit-dependent impurity scattering and from the spin-orbit coupling induced by external electric fields. The results obtained suggest that, within the framework of the extrinsic mechanisms, the anomalous Hall current in a ferromagnet may also contain a substantial amount of dissipationless contribution independent of impurity scattering. After the contribution from the spin-orbit coupling induced by external electric fields is included, the total anomalous Hall conductivity is about two times larger than that due to soin-orbit dependent impurity scatterings.     

Single output LD end-pumped passively mode-locked Nd:YVO4 laser with semiconductor saturable absorber mirror

A quarter-wave plate and the thin film polarizer(TFP) are used for the LD end-pumped passively mode-locked Nd:YVO4 laser with semiconductor saturable absorber mirror(SESAM) to obtain a single beam output with a total power of 4.8 W.An optical-optical efficiency is achieved to be 24% for a stable CW mode-locking operation at 1064 nm,with a pulse repetition rate of 70 MHz and pulse width of 16 ps.The multipulse in the pulse sequence is eliminated for reaching a peak power as high as 4 kW.     

掺Er3+氟化物光纤振荡器中红外超短脉冲的产生

基于非线性薛定谔方程建立了氟化物(ZrF₄-BaF₂-LaF₃-AlF₃-NaF, ZBLAN)光纤振荡器中产生中红外超短脉冲的理论模型, 在此基础上研究了中红外超短脉冲在氟化物光纤振荡器中形成的物理机理, 数值模拟了氟化物光纤振荡器中中红外超短脉冲的演化过程. 分析了腔内净色散和小信号增益系数对振荡器中锁模脉冲产生的影响, 并给出了参数设置范围. 研究发现: 当掺Er³⁺氟化物光纤长度, 小信号增益系数, 不饱和损耗为一定值时, 腔内净色散在一定范围内才会出现稳定的锁模脉冲, 且随着腔内净色散增加脉冲宽度变宽, 光谱变窄, 峰值功率降低; 当掺Er³⁺氟化物光纤长度及不饱和损耗一定, 腔内净色散量为合理值, 小信号增益系数在合理的范围时可以得到稳定的锁模脉冲, 且随着小信号增益系数的增加脉冲宽度变宽, 光谱变宽, 峰值功率增加.     

Remarks on interpretations of the Eotvos experiment and misinterpretation of E=mc^2

The Eotvos experiment on the verification of equivalence between inertial mass and gravitational mass of a body is famous for its accuracy. A question is, however, can these experimental results be applied to the case of a physical space in general relativity, where the space coordinates could be arbitrary？ It is pointed out that it can be validly applied because it has been proven that Einstein＇s equivalence principle for a physical space must have a frame of reference with the Euclidean-like structure. Will claimed further that such an overall accuracy can be translated into an accuracy of the equivalence between inertial mass and each type of energy. It is shown that, according to general relativity, such a claim is incorrect. The root of this problem is due to an inadequate understanding of special relativity that produced the famous equation E=mc^2, which must be understood in terms of energy conservation. Concurrently, it is pointed out that this error is a problem in Will＇s book, ‘Theory and Experiment in Gravitational Physics＇.     

First-Principles Calculations of Atomic and Electronic Properties of T1 and In on Si（111）

The atomic and electronic structures of T1 and In on Si（111） surfaces are investigated using the firstprinciples total energy calculations. Total energy optimizations show that the energetically favored structure is 1/3 ML T1 adsorbed at the T4 sites on Si（111） surfaces. The adsorption energy difference of one T1 adatom between （√3 × √3） and （1 × 1） is less than that of each In adatom. The DOS indicates that TI 6p and Si 3p electrons play a very important role in the formation of the surface states. It is concluded that the bonding of TI adatoms on Si（111） surfaces is mainly polar covalent, which is weaker than that of In on Si（111）. So T1 atom is more easy to be migrated than In atom in the same external electric field and the structures of T1 on Si（111） is prone to switch between （√3 × √3） and （1 × 1）.     

Study on the pre-chopper in CSNS LEBT

Physical designing of the pre-chopper in CSNS LEBT is carried out, which includes the deflecting voltage, the length and the width of the deflecting plates, and the gap between the deflecting plates. The most outstanding feature of the design is that both the gap and the width vary with the beam envelope size. So both the requried deflecting voltage and the loaded capacitance are lowered. In order to avoid destruction of the space charge neutralization by the pre-chopper in the whole LEBT, an electron-trapping electrode is arranged to confine the electrostatic field of the pre-chopper to the local area. To examine the reliability of the pre-chopping design in CSNS LEBT, a similar pre-chopping design in ADS RFQ LEBT is set up and an experiment on the pre-chopper is prepared. 3-dimensional simulations are carried out to determine the loaded capacitance and the applied voltage of the electron-trapping electrode.     

Entropy of Quantum Dynamical Systems and Sufficient Families in Orthomodular Lattices with Bayessian State

The purpose of the present paper is to study the entropy hs（Ф） of a quantum dynamical systems Ф = （ L, s, Ф）, where s is a bayessian state on an orthomodular lattice L. Having introduced the notion of entropy hs（ Ф, A） of partition A of a Boolean algebra B with respect to a state s and a state preserving homomorphism Ф, we prove a few results on that, define the entropy of a dynamical system hs（Ф）, and show its invariance. The concept of sufficient families is also given and we establish that hs （Ф） comes out to be equal to the supremum of hs （Ф,A）, where A varies over any sufficient family. The present theory has then been extended to the quantum dynamical system （ L, s, Ф）, which as an effect of the theory of commutators and Bell inequalities can equivalently be replaced by the dynamical system （B, s0, Ф）, where B is a Boolean algebra and so is a state on B.     

Synchronization in a Mutualism Ecosystem Induced by Noise Correlation

Understanding the cause of the synchronization of population evolution is an important issue for ecological improvement. Here we present a Lotka-Volterra-type model driven by two correlated environmental noises and show, via theoretical analysis and direct simulation, that noise correlation can induce a synchronization of the mutualists. The time series of mutual species exhibit a chaotic-like fluctuation, which is independent of the noise correlation, however, the chaotic fluctuation of mutual species ratio decreases with the noise correlation. A quantitative parameter defined for characterizing chaotic fluctuation provides a good approach to measure when the complete synchronization happens.     

Metric of States

Metric of quantum states plays an important role in quantum information theory. In this letter, we find the deep connection between quantum logic theory and quantum information theory. Using the method of quantum logic, we can get a famous inequality in quantum information theory, and we answer a question raised by S. Gudder.     

Status and accuracy of the Monte Carlo generators for luminosity measurements

The status and accuracy of the precision Monte Carlo generators used for luminosity measurements at flavour factories is reviewed. It is shown that, thanks to a considerable, long-term effort in tuned comparisons between the predictions of independent programs, as well as in the validation of the generators against the presently available calculations of the next-to-next-to-leading order QED corrections to Bhabha scattering, the theoretical accuracy reached by the most precise tools is of about one per mille. This error estimate is valid for realistic experimental cuts, appears to be quite robust and is already sufficient for very accurate luminosity measurements. However, recent progress and possible advances to further improve it are also discussed.     

Beam tail effect of a performance-enhanced EC-ITC RF gun

The beam tail effect of multi-bunches will influence the electron beam performance in a high intensity thermionic RF gun. Beam dynamic calculations that illustrate the working states of single beam tail and multi-pulse feed-in of a performance-enhanced EC-ITC （external cathode independent tunable cavity） RF gun for an FEL （free electron laser） injector are performed to estimate the extracted bunch properties. By using both Parmela and homemade MATLAB codes, the effects of a single beam tail as well as interactions of multi-pulses are analyzed, where a ring-based electron algorithm is adopted to calculated RF fields and the space-charge field. Furthermore, the procedure of unexpected deviated-energy particles mixed with an effective bunch head is described by the MATLAB code as well. As a result, the performance-enhanced EC-ITC RF gun is proved to have the capability to extract continual stable bunches suitable for a high requirement THz-FEL.     

D^0D^0 mixing and other recent charm results from BABAR

Studies in which BABAR data have shown evidence for mixing in the neutral charm meson system are presented. A new measurement of the lifetime difference parameter ycp = （1.16±0.22±0.18）% is described. Results are also presented from a systematic study of DK and D＊K invariant mass distributions from a 470 fb^-1 sample of asymmetric e^＋e^- interactions recorded by the BABAR detector at the PEP-Ⅱ storage rings. A new charmed-strange meson has been observed with mass [3044 ± 8stat （-5^＋30 ）syst] MeV/c^2 and width [239± 35stat （-42^＋46）syst]MeV/c^2.     

Coordinated Control of Multi-Agent Systems with a Varying-Velocity Leader and Input Saturation

In this paper, we investigate a leader-following tracking problem for multi-agent systems with bounded inputs. We propose a distributed bounded protocol for each follower to track a leader whose states may not be completely measured. We theoretically prove that each agent can follow the leader with estimable track errors. Finally, some numerical simulations are presented to illustrate our theoretical results.     

Pattern recognition and data mining software based on artificial neural networks applied to proton transfer in aqueous environments

In computational physics proton transfer phenomena could be viewed as pattern classification problems based on a set of input features allowing classification of the proton motion into two categories： transfer ＇occurred＇ and transfer ＇not occurred＇. The goal of this paper is to evaluate the use of artificial neural networks in the classification of proton transfer events, based on the feed-forward back propagation neural network, used as a classifier to distinguish between the two transfer cases. In this paper, we use a new developed data mining and pattern recognition tool for automating, controlling, and drawing charts of the output data of an Empirical Valence Bond existing code. The study analyzes the need for pattern recognition in aqueous proton transfer processes and how the learning approach in error back propagation （multilayer perceptron algorithms） could be satisfactorily employed in the present case. We present a tool for pattern recognition and validate the code including a real physical case study. The results of applying the artificial neural networks methodology to crowd patterns based upon selected physical properties （e.g., temperature, density） show the abilities of the network to learn proton transfer patterns corresponding to properties of the aqueous environments, which is in turn proved to be fully compatible with previous proton transfer studies.     

Design and construction progress of BRIF

A new RIB project, the Beijing Radioactive Ion-beam Facility （BRIF）, has been running at CIAE since 2004. In this project, a 100 MeV H-cyclotron, CYCIAE-100, is selected as the driving accelerator providing a 75-100 MeV, 200-500 μA proton beam. An ISOL system employs two stage separators to reach the mass resolution of 20000. Its RIB beam will be injected into the existing Tandem and a superconducting booster installed down stream of the Tandem will increase the energy by 2 MeV/q. The progress of BRIF, giving special emphasis to CYCIAE-100, will be introduced in this paper.