针对散射激光的全向激光告警系统激光威胁源定位技术研究

针对目前散射激光告警中只能定位到散射激光光斑,而不能追溯到敌方来袭激光源的现状,构建了战场环境下包括敌方威胁激光源、照射于某平台上的散射激光光斑以及全向激光告警系统在内的空间三维几何模型,推导了平台上散射激光光斑轮廓解析表达式,以及轮廓上任意一点相对鱼眼镜头的物方半视场角表达式。将成像于探测器上的光斑进行鱼眼成像畸变校正并取光斑边缘点,计算得到三维几何模型诸参数。再将模型参数与传感器阵列信息相结合,可最终获取敌方威胁激光源相对系统的方位和距离信息。最后对以上方法进行了实验验证并对产生误差的原因进行了分析。     

干涉型光纤法布里-珀罗传感系统抗噪方法的实验研究

对于干涉型光纤法布里-珀罗(FFP)传感系统,外界环境对解调干涉仪的扰动是其主要噪声源之一。在光纤布拉格光栅构成的FFP传感系统中,对比分析了采用参考传感器和参考光源两种抗噪方法。实验结果表明,对于单频和宽带干扰,两种方法均可提高信噪比到40dB。而且由于采用窄线宽光纤激光器作为参考光源的噪声水平较低,其差分探测结果具有更好的抗噪效果。     

基于天文观测的相机标定及姿态测量技术研究

为利用相机进行天文观测以实现高精度的相机姿态测量,必须先对相机参数进行精确标定。针对传统相机标定方法工作距离有限的问题,提出了以恒星为控制点的相机标定方法,根据球面天文学方法计算观测时刻控制点的世界坐标,利用摄像测量原理建立了恒星观测模型,求解相机的内外参数并分析了误差因素。实验结果表明,该标定方法在不依赖于精密、复杂的外部设备情况下可达到较高精度,并具有较强的抗噪声能力。将标定结果用于天文观测并求解相机姿态,航向角和俯仰角的解算重复性优于10″,能够满足高精度姿态测量的需求。该方法可进一步推广应用于星敏感器的标定。     

The multi-symplectic Fourier pseudospectral method for solving two-dimensional Hamiltonian PDEs

In this paper, the multi-symplectic Fourier pseudospectral (MSFP) method is generalized to solve two-dimensional Hamiltonian PDEs with periodic boundary conditions. Using the Fourier pseudospectral method in the space of the two-dimensional Hamiltonian PDE (2D-HPDE), the semi-discrete system obtained is proved to have semi-discrete multi-symplectic conservation laws and a global symplecticity conservation law. Then, the implicit midpoint rule is employed for time integration to obtain the MSFP method for the 2D-HPDE. The fully discrete multi-symplectic conservation laws are also obtained. In addition, the proposed method is applied to solve the Zakharov–Kuznetsov (ZK) equation and the Kadomtsev–Petviashvili (KP) equation. Numerical experiments on soliton solutions of the ZK equation and the KP equation show the high accuracy and effectiveness of the proposed method.     

Optimization of locally resonant acoustic metamaterials on underwater sound absorption characteristics

The study of acoustic metamaterials, also known as locally resonant sonic materials, has recently focused on the topic of underwater sound absorption. The high absorption occurs only within a narrow frequency band around the locally resonant frequency. Nevertheless, this problem can be addressed through a combination of several acoustic metamaterial layers that have different resonant frequencies. In this paper, an optimization scheme, a genetic and a general nonlinear constrained algorithm, is utilized to enhance the low-frequency underwater sound absorption of an acoustic metamaterial slab with several layers. Both the physical and structural parameters of the acoustic metamaterial slab are optimized to enlarge the absorption band. In addition, the sound absorption mechanism of the acoustic metamaterial slab is also analyzed. The result shows that each layer is found to oscillate as a nearly independent unit at its corresponding resonant frequency. The theoretical and experimental results both demonstrate that the optimized metamaterial slab can achieve a broadband (800–2500 Hz) absorption of underwater sound, which is a helpful guidance on the design of anechoic coatings.     

Experimental study on tandem pumped fiber amplifier

We present the experimental results of a 1083 nm fiber amplifier tandem pumped by 1030 nm fiber laser. The output characteristics of the tandem pumped amplifier with cladding-pump and core-pump schemes are both investigated. The 1083 nm signal laser has not been efficiently amplified when cladding-pumped by 1030 nm laser for the weak absorption of the gain fiber. The core-pump scheme works well with the amplifier. The output properties with different gain fiber length are experimentally investigated. The maximum output power is 2.4 W with power conversion efficiency of 60%.     

Phase retardation measurement by analyzing flipping points of polarization states in laser with an anisotropy feedback cavity

Phase retardation of wave plate is measured by analyzing flipping points of polarization states. Measured result and system error are analyzed. Nonlinearity of piezoelectric ceramic is an important error source. The nonlinearity is measured with an interferometer based on microchip Nd:YAG laser feedback phenomenon. The measured system of phase retardation, in this paper, is calibrated to the frequency splitting system. The accuracy of the system is improved. The measurement repeatability is better than 0.12° and the accuracy is better than 0.22°. This paper has a very important significance for wave plate high precision manufacture.     

Hollow Gaussian beam generated by beam shaping with phase-only liquid crystal spatial light modulator

Based on the refractive beam shaping system, the transformation of a quasi-Gaussian beam into a dark hollow Gaussian beam by a phase-only liquid crystal spatial light modulator (LC-SLM) is proposed. According to the energy conservation and constant optical path principle, the phase distribution of the aspheric lens and the phase-only LC-SLM can modulate the wave-front properly to generate the hollow beam. The numerical simulation results indicate that, the dark hollow intensity distribution of the output shaped beam can be maintained well for a certain propagation distance during which the dark region will not decrease whereas the ideal hollow Gaussian beam will do. By designing the phase modulation profile, which loaded into the LC-SLM carefully, the experimental results indicate that the dark hollow intensity distribution of the output shaped beam can be maintained well even at a distance much more than 550 mm from the LC-SLM, which agree with the numerical simulation results.     

Sub-200 fs microjoule pulses from a monolithic linear fiber CPA system

An all-fiber-integrated linear chirped-pulse amplifier system generating microjoule pulse energies is reported. It is seeded by an all-fiber dissipative-soliton laser and incorporates a newly developed fiber stretcher, whose dispersive properties match that of the grating compressor. Pulse durations of 189 fs with energies of 2.2 μJ were achieved after compression. The average power was 9.8 W at the repetition rate of 4.5 MHz.     

A parallel iterative solver for positive-definite systems with hybrid MPI–OpenMP parallelization for multi-core clusters

This article is devoted to the development and study of an algorithm for solving large systems of linear algebraic equations with sparse stiffness matrix on supercomputer by using the preconditioned conjugate gradient method (PCG). An efficient preconditioner is constructed on the basis of the domain decomposition method (the additive Schwarz method) which makes it possible to implement the algorithm on several computing nodes. We describe the parallel algorithm of the action of the stiffness matrix and the preconditioner on a vector. In addition, to increase the computational efficiency we make use of the routines from Intel^®MKL: the direct solver (PARDISO) and the matrix–vector multiplication for sparse matrices (Sparse BLAS). We also study efficiency of using OpenMP directives on each computational node and compare it with pure MPI parallelization. The corresponding performance and scalability charts are presented.