四孔径衍射屏在近场形成的光强分布及拓扑荷

利用基尔霍夫衍射理论计算模拟了四圆孔径衍射屏在菲涅耳深区形成的衍射光场的强度、零值线和相位的分布,发现衍射光场亮斑关于中心呈对称分布,在距离衍射屏较近的观察面上,光强值为零的点组成光强零值线段,该线段上光强等值线的离心率都接近或等于1,其两侧的光强值变化非常剧烈。复振幅的实部和虚部零值线多为封闭的曲线,零值线交叉点的个数为偶数,并且正负相位奇异点的个数相等。特殊相位奇异点周围的相位不仅呈对称分布,而且该点的拓扑荷的值近似为零。随着光波的传播,在不同的观察面上光强零值线段逐渐变短,最终趋于一点。     

Three-dimensional images generated by quadrature interferometry

Quadrature detection techniques have been applied to images obtained from a Mach-Zehnder interferometer with differently polarized beams to yield the real and the imaginary parts of the diffracted fields simultaneously. This approach eliminates the need for phase retrieval by providing complete information on the complex amplitude of the diffracted signal. We present results in which we demonstrate our ability to reconstruct two- and three-dimensional microscopic objects from their complex diffraction patterns.     

The complex phase gradient method applied to leaky Lamb waves

The classical phase gradient method applied to the characterization of the angular resonances of an immersed elastic plate, i.e., the angular poles of its reflection coefficient R, was proved to be efficient when their real parts are close to the real zeros of R and their imaginary parts are not too large compared to their real parts. This method consists of plotting the partial reflection coefficient phase derivative with respect to the sine of the incidence angle, considered as real, versus incidence angle. In the vicinity of a resonance, this curve exhibits a Breit-Wigner shape, whose minimum is located at the pole real part and whose amplitude is the inverse of its imaginary part. However, when the imaginary part is large, this method is not sufficiently accurate compared to the exact calculation of the complex angular root. An improvement of this method consists of plotting, in 3D, in the complex angle plane and at a given frequency, the angular phase derivative with respect to the real part of the sine of the incidence angle, considered as complex. When the angular pole is reached, the 3D curve shows a clear-cut transition whose position is easily obtained.     

单模激光系统输入信号后的稳态平均光强相对涨落

研究了具有实虚部间关联的量子噪声和抽运噪声驱动的单模激光系统输入信号后的统计性质,采用线性化近似方法计算了系统的稳态平均光强相对涨落,分析了量子噪声实虚部间关联系数、量子噪声强度、抽运噪声强度、输入信号振幅和频率、净增益等对稳态平均光强相对涨落的影响,发现在量子噪声实虚部间弱关联、小噪声、远离阚值、信号振幅不大和频率较高的条件下激光场的统计涨落较小。     

散斑场相位涡旋及其传播特性的实验研究

用CCD记录散斑场和参考光的干涉图样, 利用傅里叶变换法实现了散斑场复振幅以及相位分布的实验提取, 在复振幅实部零值线和虚部零值线切点处出现一种新的相位奇点, 与两条零值线交点处的传统相位奇点周围单调螺旋变化的相位分布不同, 绕切点一周的相位具有先增大后减小几乎呈对称性分布的特性, 为了解释这种新的相位奇点,提出了准孪生相位涡旋的概念. 在理论研究散斑场强度的纵向自相关函数的基础上, 实验观察散斑场相位涡旋的传播, 发现在光强纵向相关长度范围内的不同传播距离处的观察面上, 复振幅实部和虚部随机变化而涡旋的 关键词： 相位涡旋 散斑 干涉     

Transverse magneto-optical Kerr effect of Fe at the 2p excitation threshold

The transverse magneto-optical Kerr effect (T-MOKE) was investigated for thin epitaxial Fe films grown on Ag(0 0 1) in the region of the 2p excitation threshold. The experimental reflectivity and asymmetry spectra are compared to those derived from the complex dielectric function tensor calculated by using the first-principles spin-polarized relativistic band theory. We found that the T-MOKE asymmetry in general is a mixture of both the real and imaginary parts of the off-diagonal element of the dielectric function tensor, depending sensitively on the relative magnitudes of real and imaginary parts of the diagonal element. For angles of incidence larger than about 5° the influence of the Ag-substrate is significant. The major features in experimental and calculated reflectivity and asymmetry spectra are in agreement.     

大散射角散斑场中有关相位奇异新特性的研究

利用散斑场和参考光的干涉提取散斑场复振幅和相位, 研究了不同散射角下散斑场相位的分布规律以及相位奇异处光波复振幅实部零值线和虚部零值线夹角、光强等值线离心率的统计特性. 在大散射角散斑中发现了一种新的相位奇异现象, 即相位奇异线; 研究了相位在跨越奇异线时的突变规律及涡旋状相位的分布特征, 发现在相位奇异线处存在着呈双曲线或抛物线状的光强等值线.     

On some peculiarities of the energy characteristics of the interference acoustic field in a shallow sea

The results of studies of the scalar and vector energy characteristics of a real acoustic interference field in a shallow sea are presented based on notions of monochromatic fields and common field vector ratios. The importance of the quantities under consideration is that they are the components of the energy-pulse tensor of the acoustic field. The horizontal components of the complex intensity vector are represented only by its real parts, i.e., the imaginary parts of the horizontal components of the intensity vector are equal to zero; the vertical component has both real and imaginary parts. The imaginary part of the vertical component of the complex intensity vector is related to the interference field of acoustic pressure (the potential energy). The energy characteristics of the acoustic field in a shallow sea obtained during a real experiment correspond to the common theoretical field ratios.     

Self-imaging by a volume grating

The self-image phenomenon by a volume grating is proposed and theoretically analyzed. A theoretical model based on a path integral formulation to describe wave propagation through the grating inhomogeneous medium is applied. A modified version of the scalar diffraction theory Fresnel propagator is obtained which allows calculating the diffracted field amplitude by the grating. The proposed model is applied to amplitude and/or phase volume gratings. Remarkable features appear, in particular at the fractional Talbot distance 0.125z_T. In this case, if an in-phase real and imaginary grating modulation is considered a self-image intensity profile is observed for determined values of the absorptive and refractive parameters. On the other hand, a spatial comb intensity profile for a near half period shift between the real and imaginary grating modulations is found.     

First-order probability density function of the laser speckle phase

An expression for the first-order probability density function of the laser speckle phase is analytically derived under the assumption that the speckle field obeys a non-circular, complex Gaussian, random process with a certain correlation between the real and imaginary parts of its complex amplitude. The probability density function of the speckle phase is actually evaluated for various cases and shown three-dimensionally as a function of the standard deviation of random object phase variations. The effect of random object phase variations on the probability density function is also investigated in detail.     

New amplitude equation of single—mode laser

The white-gain model and the white-loss model of a single-mode laser are investigated in the presence of cross-correlations between the real and imaginary parts of quantum noise as well as pump noise. It was found that, like the white cubic model (2001 Chin. Phys. Lett. 18 370), the amplitude equations are all decoupled from the phase equations for the two models, and the same novel term appears in the amplitude equations of the two models. So we can put the amplitude equations of all the models into a general form, that is, the new amplitude equation. We further use this new amplitude equation to study specifically the stationary properties of the laser intensity for the white-gain model.     

Complex resonance and complex-frequency spectroscopy

The response of a medium to radiation with a complex frequency corresponding to an exponential time decrease in the radiation amplitude has been analyzed. The effect of complex resonance has been demonstrated when the real and imaginary parts of the complex radiation frequency approach the real and imaginary parts of the complex frequency of damping natural oscillations of medium oscillators. In resonance itself, the absolute value of the refractive index is divergent and radiation is completely reflected from the medium boundary. It has been shown that scanning of not only the real part, but also the imaginary part of the probe radiation frequency expands the capabilities of spectroscopy and makes it possible to, e.g., distinguish resonances even with coinciding (real) frequencies and close (of the same order of magnitude) widths.     

Effects of correlations between the real and imaginary parts of quantum noise on intensity fluctuation for a saturation laser model

This paper studies the effects of cross-correlations between the real and imaginary parts of quantum noise on the laser intensity in a saturation laser model. It derives the analytic expressions of the intensity correlation function ${C(\tau)}$ and the associated relaxation time ${T({C})}$ in the case of a stable locked phase resulting from the cross-correlation ${\lambda_q}$ between the real and imaginary parts of quantum noise. Based on numerical computations it finds that the presence of cross correlations between the real and imaginary parts of quantum noise slow down the decay of intensity fluctuation, i.e., it causes the increase of intensity fluctuation.     

Effects of correlations between the real and imaginary parts of quantum noise on intensity fluctuation for a saturation laser model

This paper studies the effects of cross-correlations between the real and imaginary parts of quantum noise on the laser intensity in a saturation laser model. It derives the analytic expressions of the intensity correlation function C（τ） and the associated relaxation time T（C） in the case of a stable locked phase resulting from the cross-correlation λq between the real and imaginary parts of quantum noise. Based on numerical computations it finds that the presence of cross correlations between the real and imaginary parts of quantum noise slow down the decay of intensity fluctuation, i.e., it causes the increase of intensity fluctuation.     

强散射体产生的像面散斑对比度与随机表面及成像系统关系的研究

在对4f光学成像系统中强散射体形成的像面散斑的统计特性的研究中, 首先通过散斑场光波复振幅的一般形式和双重指数函数近似求出散斑光强的系综平均, 然后利用散斑场光波复振幅的实部和虚部的旋转变换法求出散斑光强的方差, 最后得出了散斑对比度与随机表面统计参量和系统参量的直接表达式. 本结果与现有文献中包含随机表面相关面积或散射粒子数目的隐含表达式相比具有明显的改进, 并对标定随机表面的散斑对比度法具有重要意义. 关键词： 随机表面 像面散斑 对比度     

存在球差和失焦下电子光学传递函数和脉冲响应函数

根据电子光学理论,球差和失焦引起附加相位移为γ,相干的振幅和相位衬度传递函数为cosγ和sinγ。它们的傅里叶逆变换给出脉冲响应函数的实部和虚部。本文讨论了cosγ和sinγ的零点和极值点,这些点将衍射平面划分为一系列环带。证明了当无量纲失焦量Δ=N^1/2(N为正整数)时各环带上cosγ,sinγ的积分相同,即对脉冲响应函数中心值的贡献相同。本文讨论了使cosγ或sinγ的积分取极大值或极小值,亦即使脉冲响应函数中心值或中心强度取极大值或极小值的条件。本文还讨论了脉冲响应函数最佳均方 关键词：     

Determination of displacement derivative in digital holographic interferometry

Digital holography (DH) and digital shearography (DS) both play an important role in non-destructive evaluation. In this paper, a novel method based on digital holographic interferometry (DHI) and complex phasor (CP) is proposed to determine displacement derivative. An algorithm is employed to filter the imaginary and real parts of complex values without the need of direct phase manipulation. Two-dimensional short time Fourier transform (STFT) is employed subsequently to process wrapped phase maps. An experiment is conducted to demonstrate the validity of the proposed method.     

Distribution characteristics of intensity and phase vortices of speckle fields produced by N-pinhole random screens

We analyze the distribution properties of phase and phase vortices in a speckle field generated by N-pinhole random screens, and find that the phase vortex distributions show similarity and clustering in local regions. The phase patterns have a lot of sets composed of two phase vortices with opposite signs or four phase vortices which are positive and negative vortices alternately. Cases are also found where two adjacent phase vortices have the same topological charges. The density of phase vortices becomes larger with the increase of the radius of circumference and the number of pinholes on screen.Then, the relative positions of phase vortices can be adjusted by changing the radius of circumference and the number of pinholes.     

Unitarisation and black-disk limit at the LHC in the presence of a hard pomeron

Recent models of soft diffraction include a hard pomeron pole besides the usual soft term. Such models violate the black-disk limit around Tevatron energies, so that they need to be supplemented by a unitarisation scheme. Two standard schemes are considered in this Letter, and we show that they lead to an uncertainty at the LHC much larger than previously estimated. We also examine the signature of unitarisation on various small-t observables, the slope in t of the elastic cross section, or the ratio of the real to imaginary parts of the scattering amplitude, and show that the existence of a unitarised hard pomeron in soft scattering may be confirmed by LHC data.     

Steady-State Analysis of a Two-Mode Laser System with Cross-Correlation Between Real and Imaginary Parts of Quantum Noise

An inhomogeneously broadened two-mode laser system with cross-correlations between the real and imag- inary parts of quantum noise is considered. The Fokker-Planek equation of the system is derived by the phase-locking method. The steady-state probability distribution, the mean light intensity, the normalization autocorrelation function, and cross correlation function are calculated. The results indicate that： （i） The cross-correlation between the real and imaginary parts of quantum noise can cause the stationary probability distribution from one peak structure to two extrema structure when the laser system is operated above threshold; （ii） The cross-correlation between the real and imaginary parts of quantum noise enhance the light intensity fluctuation and decrease the laser output when the laser system is operated below or near threshold; （iii） The effect of the cross-correlation between the real and imaginary parts of quantum noise is very weak on the stationary properties when the laser system is operated far above threshold.