小尺寸平面源的误差精确分析

基于Helmholtz方程的严格远场解和源的“误差面积”描述方法,讨论了大发散角光辐射远场振幅和相位对于源包络扰动的依赖关系,讨论了由于源振幅扰动而产生的远场误差,建立了一种恰当的描述远场误差的方法.模拟实验表明,在“相对误差面积”的基础上,可以结合利用“离轴距离”来精确描述源误差和分析远场误差,利用“判据点”可以判断离轴误差的存在.     

非傍轴LG_(00)模与LG_(10)模高斯光束的远场分布特性

基于扁椭球面坐标系下非傍轴高斯光束的电场分布表达式,给出非傍轴LG_(10)模高斯光束的远场电场振幅分布表达式;分析了非傍轴LG_(00)模和LG_(10)模高斯光束的远场电场振幅分布特性;计算了非傍轴与傍轴高斯光束远场电场振幅分布的匹配效率和二阶矩参量的相对计算误差。分析表明,当扁椭球坐标系的半焦距远大于波长时,非傍轴LG_(00)模和LG_(10)模高斯光束的远场电场振幅分布趋近于傍轴LG_(00)模和LG_(10)模高斯光束的远场电场振幅分布。     

远轴高斯波

基于严格求解Helmholtz方程的远场解，提出了一种描述远轴高斯光波传播的新方法．给出了高斯光波振幅、相位分布公式，讨论了光斑尺寸、发散角和能量守恒等关系．并指出任何高斯波的最大光束发散角为65.5°． 关键词：     

激光束畸变波前高频相位的恢复效果分析

运用逐次逼近迭代法恢复近场畸变波前的高频相位,定量分析了高频相位恢复效果与滤波器截止频率之间的关系,并进一步讨论了近场和远场光强噪声扰动对恢复效果的影响。研究结果表明:随着滤波器截止频率的增大,即对近场波前相位探测器要求的提高,逐次逼近迭代法的高频相位恢复效果会越来越好。此外,高频相位恢复效果随近场或远场光强噪声扰动的增大而变差,其中,近场光强噪声扰动对恢复效果的影响相对较小,而远场光强噪声扰动对恢复效果的影响则明显得多。在实际工作中,为了获得较好的近场高频相位的恢复效果,不仅需要合理地对近场低频相位测量提出要求,而且还必须尽可能减小光强分布测量的误差,特别是尽量减小远场噪声光强的影响。     

基于远场的拼接光栅压缩池的设计

 利用傅里叶光学方法得到了失调拼接光栅压缩池输出光束的远场振幅表达式,建立了分析拼接光栅的各种误差的理论模型,得到了拼接误差对脉冲的影响是附加相位延迟和角度偏转。在要求远场的一倍衍射极限区域的积分能量分布达到理想情况下的90％的条件下,对于含有口径为40 cm、脉宽为0.1~10 ps脉冲的系统进行分析并分别得到了各种误差的容限。     

有振幅调制和相位畸变光束的远场光谱移动与光谱开关

基于瑞利衍射公式,研究了被光阑衍射的具有振幅调制和相位畸变光束的远场光谱变化规律。结果表明,有振幅调制和相位畸变光束在远场也会出现光谱异变现象和光谱开关效应,光阑截断参数、光束的相位畸变参数、振幅调制参数、光强调制参数对远场光谱的跃迁量和光谱开关产生影响。通过数值计算结果分析讨论了光阑截断参数及光束各参数影响远场光谱的规律。     

洛仑兹脉冲光束的复振幅包络解和复解析信号解的比较研究

使用复振幅包络表示式和复解析信号表示式推导了洛仑兹脉冲光束的传输公式. 通过具体数 值计算对脉冲光束的复振幅包络解和复解析信号解在不同带宽时的传输进行了对比研究. 数 值结果表明脉冲光束为窄带时，在传输方向轴中心的一定范围内两种解是一致的，而对于宽 带脉冲光束，复振幅包络解在轴中心较近的距离即表现出奇异性，复解析信号解才是符合物 理意义的表示式. 由数值计算得出了选择脉冲光束研究方法的条件，并从所得公式对复振幅 包络解出现奇异性的现象进行了解释. 关键词： 复振幅包络 复解析信号 窄带脉冲 宽带脉冲     

光纤激光相干阵列远场光强分布的影响分析

在光纤激光相干组束中,受到各种因素的影响,各个单元激光器出射激光的相位、振幅和偏振态不能保持一致,并随着时间而变化,均会降低相干组束后的光束质量、减弱光束中心的峰值光强和中心区域内的功率.针对光纤激光相干组束中每个单元光束的出射时的相位、振幅和偏振方向扰动对相干组束远场光强分布的影响进行了理论分析,并给出数值计算结果.结果表明远场光强分布的图形、峰值光强度和中心区域内的功率,受到各因素的影响,都会不同程度的变差或减弱.     

正弦高斯涡旋光束的远场传输特性

根据角谱法和稳相法,推导了正弦高斯涡旋光束TE波和TM波在远场传输和能流密度的解析表达式,研究了正弦高斯涡旋光束在远场中的相位奇点和能流密度分布.结果表明:正弦高斯涡旋光束的远场特性与高斯光束的束腰宽度、涡旋离轴量、坐标位置以及与正弦项相关的参量有关.在一定条件下,远场中会出现相位奇点和能流密度黑核;当控制参量改变时,相位奇点和黑核的位置会发生移动,但原点处不受影响.相位奇点和能流密度的对称性主要受涡旋离轴量影响,当涡旋离轴量为0时,相位奇点和能流密度分布关于原点对称;当涡旋离轴量改变时,相位奇点和能流密度分布呈现出非对称性.     

相位敏感光时域反射系统的时钟同源I/Q解调方法

提出一种基于时钟同源I/Q解调的相位敏感光时域反射系统解调方法.分析了调制信号与混频信号非同源不一致对解调结果的影响,采用声光调制器调制信号、斩波信号与I/Q混频信号时钟同源的方法以消除残余频率的影响.实验采用双压电陶瓷作为扰动源,通过I/Q解调实时获得后向瑞利散射光幅值和相位,进而实现扰动的定位和还原.实验结果表明,该系统能有效地探测到5km和9km处的正弦扰动,定位信号信噪比分别达17.8dB和16dB,相位解调结果准确还原正弦扰动,与正弦曲线的拟合系数分别为0.994和0.991,均方根误差分别为0.116和0.141.实验进一步验证了该方法能够测得不同扰动幅度下的相位正弦变化曲线,并能准确得到不同扰动频率,且扰动位置处相位变化幅度与扰动强度具有良好的线性关系,线性拟合系数达0.992,均方根误差为0.499,均优于非同源解调结果.     

Linear stability analysis on a spherical particle growing from a binary melt under the far-field flow

The solutions of temperature and solute fields around a spherical crystal growing from a binary melt under the far-field flow are obtained.Based on the results,a linear stability analysis on the spherical interface growing from the binary melt under the far-field flow is performed.It is found that the constitutional supercooling effect ahead of the spherical crystal interface under the far-field flow is enhanced compared with that without the flow.The growth rate of the perturbation amplitude at the up-wind side of the spherical crystal interface is larger than that at the down-wind side.The critical stability radius of the crystal interface decreases with the increasing far-field flow velocity.Under the far-field flow,the whole spherical interface becomes more unstable compared with that without the flow.     

影响连续相位板聚焦性能的主要因素

为提高惯性约束聚变系统中聚焦光斑的能量集中度,分析了在应用过程中影响连续相位板性能的主要误差来源,并建立了相应的数学模型。通过分析得出存在误差时远场焦斑的能量集中度和均方根值,且口径误差、对准误差、振幅畸变误差对连续相位板的聚焦性能影响很小,波前畸变影响能量集中度的权重最大。进一步分析可知:当畸变波前相关长度与连续相位板的最小空间周期（10 mm左右）相当时,畸变波前极大地影响激光的聚焦性能,提高惯性约束聚变系统中畸变波前的相关长度是提高聚焦光斑的能量集中度的有效方法。     

Temporal and spatial chaos in the Kerr-AdS black hole in an extended phase space

Based on the Melnikov method, we investigate chaotic behaviors in the extended thermodynamic phase space for a slowly rotating Kerr-AdS black hole under temporal and spatial perturbations. Our results show that the temporal perturbation coming from a thermal quench of the spinodal region in the phase diagram may cause temporal chaos only when the perturbation amplitude is above a critical value, which involves the angular momentum J. Under the spatial perturbation, however, it is found that spatial chaos always occurs, independent of the perturbation amplitude.     

Wave field synthesis of moving virtual sound sources with complex radiation properties

An approach to the synthesis of moving virtual sound sources with complex radiation properties in wave field synthesis is presented. The approach exploits the fact that any stationary sound source of finite spatial extent radiates spherical waves at sufficient distance. The angular dependency of the radiation properties of the source under consideration is reflected by the amplitude and phase distribution on the spherical wave fronts. The sound field emitted by a uniformly moving monopole source is derived and the far-field radiation properties of the complex virtual source under consideration are incorporated in order to derive a closed-form expression for the loudspeaker driving signal. The results are illustrated via numerical simulations of the synthesis of the sound field of a sample moving complex virtual source.     

Source-filter Comparison of Measurements of Fundamental Frequency Perturbation and Amplitude Perturbation for Synthesized Voice Signals

SUMMARY: An investigation of the effect of glottal source aperiodicities (jitter, shimmer, and aspiration noise) on the estimation of fundamental frequency (f0) perturbation and amplitude perturbation, of synthesized, glottal source and voiced speech waveforms, is considered. Firstly, 4, cycle-event f0 estimators are examined: (1) waveform matching of the low-pass filtered waveform, (2) positive peaks (PPs) from the speech waveform, (3) PPs from the low-pass filtered waveform, and (4) positive zero crossings from the low-pass filtered waveform. The analysis shows that f0 perturbation measures taken from the low-pass filtered waveform are affected by both amplitude perturbation and random glottal noise, whereas, f0 perturbation measures taken from the PPs of the original waveform are affected by noise but not by amplitude perturbation. It is shown for the low-pass filter methods that the effects of amplitude perturbation and noise lead to increased errors in the measurement of f0 perturbation for the synthesized speech waveforms when compared with the synthesized glottal waveforms. Shimmer of the synthesized speech waveform is approximately equal to shimmer of the synthesized glottal source. However, noise and jitter affect measures of amplitude perturbation. The estimation of f0 perturbation from the synthesized speech waveform is shown to be nonlinearly related to f0 perturbation estimation from the synthesized glottal waveform as a consequence of the filtering action of the vocal tract. Low-pass filtering the voiced speech waveform is shown to provide a partial solution to this problem.     

The field of an equivalent multipole composite radiator in a waveguide

The possibility of replacing a spatially extended volume low-frequency sound source, which forms a three-dimensional directional field in the far-field zone, by an equivalent multipole source is considered. Developing the ideas of L.M. Brekhovskikh, who obtained the solution for a monopole, exact and simplified models of the source field are constructed in the form of superpositions of multipoles of various orders. The models are considered in the integral, mode, and ray approximations applied to the unbounded space and homogeneous and plane-layered waveguides. The results of computations are presented, and the conclusion is made that the contribution of the vertical dipole and quadrupole components to the interference structure of the field amplitude in a waveguide decreases with an increase in the distance from the source. The phase structure is found to be stable regardless of the type of the complex multipole source.     

散射条件下声源分离及参数获取的平行障板方法*

声纳系统或水声设备湿端不可避免存在某些散射体,克服散射体干扰对声源本身辐射特性进行测量目前还缺乏简捷有效的方法。依据刚性圆盘散射规律,通过有限元建模分析了与观察方向平行布设的刚性圆盘对声源辐射特性的影响规律,结果表明：在满足远场条件时,在较小的允许误差范围内观察轴线上声压幅值分布与引入平行障板无关。并在此基础上尝试提出一种简捷有效的平行障板方法,实现散射条件下声源分离与参数获取。通过有限元仿真分析,在1~20kHz频率范围内,半径0.4m厚8mm的钢板对脉动圆管声源级分离测量引入误差在±0.6dB以内。     

The possibility of using the equivalent plane wave model to increase the efficiency of taking bearings of low-frequency signals in shallow water

The possibility of approximating the sound field in the region of interference maxima using the equivalent plane wave model with the actual amplitude and the average ??effective?? phase velocity calculated or measured by the phase gradient at the array aperture is discussed. The method is substantiated by studying the mode, interference, and phase structures of the low-frequency sound field along with the spatial responses of an extended linear array. For bottom-moored or towed geophysical arrays whose sizes are large compared to the wavelength, both the necessity and the possibility of reducing the error in taking the bearing of a sound source in a waveguide are justified. The use of the proposed model is recommended for approximate matching of the array to the transfer function of the waveguide to reduce the bearing error.