共查询到20条相似文献,搜索用时 15 毫秒
1.
A theoretical model is developed which characterizes the physical process responsible for generating ultra-short, high-energy, mode-locked pulses in a normal GVD laser cavity with spectral filtering. Two physical parameters are critical to achieving optimal performance: the ratio of the filter bandwidth to the gain bandwidth and the placement of the output coupler in the laser cavity. The spectral filtering allows for the high-energy of typical normal GVD laser cavities to be maintained while the pulse intensity doubles and the FWHM reduces by an order of magnitude. This phenomenon is generic and ubiquitous to normal GVD mode-locking. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
2.
P. Nguyen P. Skovgaard M.P. Srensen P.L. Christiansen 《Chaos, solitons, and fractals》1995,5(12):2475-2483
Soliton propagation in a laser fibre is investigated using multiple-scale perturbation analysis. The perturbative terms are linear loss and saturable nonlinear gain. Furthermore, we show the possibility of stable soliton-like propagation in an amplitude pulse mode-locked system consisting of a semiconductor laser coupled to a nonlinear fibre through a centre mirror. The soliton-like pulse is slightly asymmetric due to asymmetric gain amplification in the semiconductor laser. 相似文献
3.
G. H. M. van der Heijden 《Journal of Nonlinear Science》1995,5(3):257-283
Summary We present a computer-assisted study of the dynamics of two nonlinearly coupled driven oscillators with rotational symmetry which arise in rotordynamics (the nonlinearity coming from bearing clearance). The nonlinearity causes a splitting of the twofold degenerate natural frequency of the associated linear model, leading to three interacting frequencies in the system. Partial mode-locking then yields a biinfinite series of attracting invariant 2-tori carrying (quasi-) periodic motion.Due to the resonance nature, the (quasi-) periodic solutions become periodic in a corotating coordinate system. They can be viewed as entrainments of periodic solutions of the associated linear problem. One presumably infinite family is generated by (scaled) driving frequencies = 1+2/n,n = 1,2,3,...; another one is generated by frequencies =m,m = 4,5,6,... Both integersn andm can be related to discrete symmetry properties of the particular periodic solutions.Under a perturbation that breaks the rotational symmetry, more complicated behavior is possible. In particular, a second rational relation between the frequencies can be established, resulting in fully mode-locked periodic motion. 相似文献
4.
Q-switching is considered as a favorable technology to generate short duration and high peak power pulses, which is widely used in industry. We derive a new model to simulate passively Q-switched solid state lasers in a three-dimensional (3D) space. In our model, several Gaussian modes are considered. Compared with single-mode models, 3D multimode models are much more capable of reflecting laser behaviors. In our modeling, the single-mode system is extended to a multimode system, which calculates photon numbers for different modes separately. In order to realize the numerical simulation of our multimode model, we apply a finite volume discretization respectively to the gain medium and saturable absorber, then the discretized multimode passively Q-switched laser system is obtained. The numerical results and applications of our model are shown at the end of the paper. The modeling and simulation of passively Q-switched solid state lasers can help to optimize laser designs. 相似文献
5.
研究了一个激光脉冲放大器增益通量系统解的问题.首先讨论了较一般的系统, 然后引入一个同伦映射.再利用映射的性质, 引进一个人工参数, 将求解非线性问题转化为求解一系列线性问题.再逐次地求出对应的线性问题的解, 最后得到了原模型解的近似展开式.可以看出, 同伦映射方法是一个解析的方法.它是通过函数的解析运算并用初等函数来表达近似解,其不同于用离散数值运算的数值计算方法.因此通过同伦映射解, 还可以对它继续进行解析运算, 从而可以进行微分和积分等运算来得到与激光脉冲放大器增益通量相关的其他物理量的性态. 相似文献
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《Communications in Nonlinear Science & Numerical Simulation》2014,19(12):4094-4104
In this paper, an efficient self-adaptive model for chaotic image encryption algorithm is proposed. With the help of the classical structure of permutation-diffusion and double simple two-dimensional chaotic systems, an efficient and fast encryption algorithm is designed. However, different from most of the existing methods which are found insecure upon chosen-plaintext or known-plaintext attack in the process of permutation or diffusion, the keystream generated in both operations of our method is dependent on the plain-image. Therefore, different plain-images will have different keystreams in both processes even just only a bit is changed in the plain-image. This design can solve the problem of fixed chaotic sequence produced by the same initial conditions but for different images. Moreover, the operation speed is high because complex mathematical methods, such as Runge–Kutta method, of solving the high-dimensional partial differential equations are avoided. Numerical experiments show that the proposed self-adaptive method can well resist against chosen-plaintext and known-plaintext attacks, and has high security and efficiency. 相似文献
8.
Neuron as the main information carrier in neural systems is able to generate diverse spiking trains in response to different stimuli. Neuronal spiking patterns are related to the information processing in neural system. This paper investigates the dynamical behaviors of a two-dimensional minimal neuron model exposed to externally-applied extremely low frequency (ELF) sinusoidal electric field (EF). By numerical stimulation, it is found that neuron can exhibit different spiking patterns such as p:q mode-locking (i.e. a periodic oscillation defined as p action potentials generated by q cycle stimulations) and chaotic behaviors, depending on the values of stimulus frequencies. Transitions between different spiking patterns during exposure to the external EF are explored by interspike intervals (ISIs) and average firing rate. It is found that frequencies of the external EF can act as a bifurcation parameter, whose small change can cause the transition in neuronal behaviors. It is shown that a rich bifurcation structure including period-adding without chaos and mode-locking alternated with chaos suggests frequency discrimination of the neuronal firing patterns. Our results can provide a useful insight into the organization of similar bifurcation structures in excitable systems such as neurons under periodic forcing. Through detail analysis of the spiking patterns, we have explained how neuron’s information (spiking patterns) encodes the stimulus information (frequency), and vice versa. 相似文献
9.
Bixue Hou Guofu Chen Zhiqi Hao Shan Feng Shuyan Wang Yishan Wang Guozhi Wang 《中国科学A辑(英文版)》1999,42(8):852-858
The experimental results of imaging through flesh tissue using fs electronic holographic gating method is reported. In the
experiment, Ti: sapphire mode-locked laser is used as light source, of which the repetition rate is 100 MHz, central wavelength
800 nm, duration of pulse 20 fs, output power 80 mW. Tissue is a 7 mm thick chicken slice, and the imaged object is a metal
wire with diameter of 0.5 mm. A general CCD is used to record holograms and a clear image of metal wire is obtained. Several
relevant problems are discussed. 相似文献
10.
W. C. Nieuwpoort R. Bleekrode 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1965,16(1):101-106
The concept of a chemical laser is discussed and a preferable definition is proposed. In order to obtain some insight into the feasibility of chemical pumping in general and into the orders of magnitude of the parameters involved, the consequences of a simple model, more or less related to a stationary flamelaser, are explored.According to this model i) a lower limit depending on flow velocity and wavelength exists for the rate at which production and radiative processes may proceed, and ii) the available gain can very appreciably exceed the critical value needed for laser action if certain conditions are satisfied.The assumptions underlying the model and its results, and their applicability in practice are briefly discussed. 相似文献
11.
The numerical integration of Hamiltonian systems with multi-frequency and multidimensional oscillatory solutions is encountered frequently in many fields of the applied sciences. In this paper, we firstly summarize the extended Runge–Kutta–Nyström (ERKN) methods proposed by Wu et al. (Comput. Phys. Comm. 181:1873–1887, (2010)) for multi-frequency and multidimensional oscillatory systems and restate the order conditions and symplecticity conditions for the explicit ERKN methods. Secondly, we devote to exploring the explicit symplectic multi-frequency and multidimensional ERKN methods of order five based on the symplecticity conditions and order conditions. A five-stage explicit symplectic multi-frequency and multidimensional ERKN method of order five with some small residuals is proposed and its stability and phase properties are analyzed. It is shown that the new method is dispersive of order six. Numerical experiments are carried out and the numerical results demonstrate that the new method is much more efficient than the methods appeared in the scientific literature. 相似文献
12.
针对自动化集装箱码头水平作业的AGV调度问题(AGVSP),在解决整体作业优化的同时,考虑AGV作业行为对作业效率及能耗的影响,建立以AGV作业效率以及能源消耗作为双目标的双层规划模型。该模型考虑了独立装卸与同步装卸两种模式下的AGV水平运输的特点。在此基础上,设计了对应的双层遗传算法进行求解。并通过数值实验,对模型在考虑行为与不考虑行为,独立作业与同步装卸作业模式下的作业效果进行验证比较。结果表明:本模型在不影响作业效率的前提下,可有效降低AGV的作业能耗。 相似文献
13.
Kai Liu & Xinyuan Wu 《计算数学(英文版)》2015,33(4):356-378
The multi-frequency and multi-dimensional adapted Runge-Kutta-Nyström (ARKN)
integrators, and multi-frequency and multi-dimensional extended Runge-Kutta-Nyström(ERKN) integrators have been developed to efficiently solve multi-frequency oscillatory
Hamiltonian systems. The aim of this paper is to analyze and derive high-order symplectic and symmetric composition methods based on the ARKN integrators and ERKN
integrators. We first consider the symplecticity conditions for the multi-frequency and
multi-dimensional ARKN integrators. We then analyze the symplecticity of the adjoint integrators of the multi-frequency and multi-dimensional symplectic ARKN integrators and
ERKN integrators, respectively. On the basis of the theoretical analysis and by using the
idea of composition methods, we derive and propose four new high-order symplectic and
symmetric methods for the multi-frequency oscillatory Hamiltonian systems. The numerical results accompanied in this paper quantitatively show the advantage and efficiency of
the proposed high-order symplectic and symmetric methods. 相似文献
14.
The flow through corrugated pipes is known to lead to strong whistling tones which may be harmful in many industrial appliances. The mechanism is known to originate from a coupling between vortex shedding at the edges of the cavities forming the wall of the tube and the acoustical modes of the pipe. The latter depend upon the effective velocity of sound ceff within the corrugated pipe. The purpose of this paper is to compute accurately this effective velocity of sound through an asymptotic calculation valid in the long-wave limit. Results are given for a number of geometries used in previous works, and compared with a simple model in which the effective speed of sound is function of the geometry of the pipe. The latter is found to work best for short cavities but significant disagreement is found for longer cavities. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
15.
针对不同时段内被评价对象增益的不同,提出了一种基于"又好又快发展"思想的动态综合评价方法.首先依据时序立体数据信息,求出被评价对象的增益水平;然后通过均值相对运算、规范化和一致性运算,定义出各被评价对象各指标在某一时刻的相对发展增益权、均衡发展增益权和可持续发展增益权,并进一步计算综合增益权;最后依据激励思想给出增益权与静态综合评价值的合成规则.通过2006-2010年中部六省三次产业"又好又快发展"水平评价的实例分析,证明了方法的科学性. 相似文献
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The long-time near-conservation of the total and oscillatory energies of numerical integrators for Hamiltonian systems with
highly oscillatory solutions is studied in this paper. The numerical methods considered are symmetric trigonometric integrators
and the St?rmer–Verlet method. Previously obtained results for systems with a single high frequency are extended to the multi-frequency
case, and new insight into the long-time behaviour of numerical solutions is gained for resonant frequencies. The results
are obtained using modulated multi-frequency Fourier expansions and the Hamiltonian-like structure of the modulation system.
A brief discussion of conservation properties in the continuous problem is also included.
AMS subject classification (2000) 65L05, 65P10 相似文献
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Linda C. van der Gaag Hermi J.M. Tabachneck-Schijf 《International Journal of Approximate Reasoning》2010,51(2):196-208
The next development in building Bayesian networks will most likely entail constructing multi-purpose models that can be employed for varying tasks and by different types of user. In this position paper, we argue that the development of a special type of ontology to organize the knowledge involved in such a multi-purpose model is crucial for the management of the model’s content. This ontology should preserve all knowledge elicited for the construction of the model and be accessible to domain experts and knowledge engineers alike. Based on the different ways in which people learn and gain expertise, we further argue that knowledge elicitation will result in task-specific knowledge mostly, which is best stored in the format in which it is elicited. To support varying model views for different tasks and different types of user, we propose that the elicited knowledge be organized in a library-style ontology of separate modules. 相似文献
20.
In this paper, the operation of π-phase shifted distributed feedback Raman fiber (DFB-RF) laser above threshold condition is analyzed theoretically. The nonlinear optical phenomena such as self phase modulation (SPM) and cross phase modulation (XPM) have significant effect on the performance of DFB-RF laser. The numerical results show that the nonlinear effects cause to the saturation of output power and the value of saturated power is dependent on the fiber length. It is found that, the operation wavelength of stokes modes of DFB-RF laser varies in above threshold condition as a result of nonlinear optical properties of the fiber. Simulation is performed by using transfer matrix method to solve three coupled nonlinear wave equations which describe the propagation of pump, forward and backward Stokes waves. The nonlinear SPM and XPM effects are considered in the presented theoretical model. 相似文献