Study on measurement technology of ultra-low brightness北大核心CSCD

光亮度是表征发光体的重要光度特性参数。提出了一种超低亮度计的设计方法,描述了超低亮度计的工作原理和组成;利用微弱光信号处理技术、非线性校准技术、制冷散热技术等实现了超低亮度的自动测量;根据亮度计的测量原理,对仪器进行了标定,测量不确定度达到5%。超低亮度计可适用于实验室和现场等测试场所,为微光夜视装备、显示系统、特种光源、发光材料等的性能评估测试和校准提供计量保障。     

Calculation algorithm of high-precision two-dimensional broadband laser warning parameters北大核心CSCD

High precision grating diffraction laser warning system is a photoelectric countermeasure equipment to judge and locate the incoming laser function. In order to improve the positioning accuracy, an improved algorithm for calculating and fitting the calculation parameters of the spot center was proposed. Firstly, the laser spot was preprocessed, and the center coordinates of the connected area were obtained by using the improved connected area marking algorithm and spot center extraction algorithm. Secondly, the azimuth angle and pitch angle were set, the images were collected and the spot center was calculated, and the pixel horizontal and vertical coordinates in x and y direction as well as fitting surfaces of laser parameters were fitted, so as to judge the azimuth angle, pitch angle and wavelength of the incoming laser. Finally, the improved connected area marking algorithm, spot center extraction algorithm and parameter fitting calculation results were compared with the traditional algorithm. The experimental results show that the pitch angle error between the fitting calculation results and the real data is less than 0.4°, and the azimuth angle error is less than 0.2°, which greatly improves the accuracy of laser direction recognition. Copyright ©2022 Journal of Applied Optics. All rights reserved.     

Definition and measurement of the beam propagation factor M~2 for chromatic laser beams

The concept of the beam propagation factor M2 is extended for chromatic laser beams. The definition of the beam propagation factor can be generalized with the weighted effective wavelength. Using the new definition of factor M2, the propagation of chromatic beams can be analyzed by the beam propagation factor M2 as same as that of monochromatic beams. A simple method to measure the chromatic beam factor M2 is demonstrated. The chromatic factor M2 is found invariable while the laser beam propagates through the dispersion-free ABCD system.     

Electron density measurement of laser-induced epoxy fiber reinforced polymer plasma北大核心CSCD

Interferograms of laser-induced epoxy fiber reinforced polymer plasmas are obtained through aMach-Zehnder interferometry system. An improved digital double-exposure Fourier method is applied to extractinitial wrapped phases from interferograms, and then an improved phase unwrapping algorithm based on a maskand a branch-cut method is proposed to solve the problem of phase unwrapping. After the inverse Abel transfor-mation of the unwrapped phase, spatial distributions of the electron density of laser-induced epoxy fiber rein-forced polymer plasma at various delays are acquired. Results show that the measured electron density of theplasma is mainly distributed on the order of 10^18 cm^3. The experiment also indicates that the total amount oflaser plasma electrons changes slightly within the recorded time and the change of the electron density is approx-imately inversely proportional to the change of the plasma volume.     

Role of beam propagation in Goos-Hänchen and Imbert-Fedorov shifts

We derive the polarization-dependent displacements parallel and perpendicular to the plane of incidence for a Gaussian light beam reflected from a planar interface, taking into account the propagation of the beam. Using a classical-optics formalism we show that beam propagation may greatly affect both Goos-H?nchen and Imbert-Fedorov shifts when the incident beam is focused.     

Sound propagation in ducts with spatially variant parameters

The one-dimensional theory of sound propagation in ducts isgeneralized and investigated in this paper.It can be assumed that anyduct system consists of two kinds of elementary structures:One is thepiped structure in which the characteristics,such as the acousticalparameter on the interior surface of the wall,the cross-section area andthe aerodynamic parameters of the flow,etc.,will vary continuously andslowly with distance along the axis of the duct.The other is the localstructure with discontinuity in which the characteristics will change abruptly.The acoustical properties of both structures are analysed in generalcases based upon the fundamental equations of aerodynamics,and theirtransmission matrixes are derived and discussed respectively.Two typicalexamples are analysed and discussed.     

Comparison between relay propagation and direct propagation of Gaussian-Schell-model beam in turbulent atmosphere along a slant path

The relay propagation of Gaussian-Schell-model in turbulent atmosphere along a slant path is studied in this paper. Based on the extended Huygens-Fresnel principle and a quadratic approximation, an analytical formula of average intensity for Gaussian-Schell-model beams in turbulent atmosphere along a slant path is derived, and some special cases are discussed. From the study and the comparison with the direct propagation, we can see that the relay propagation has an advantage over the direct propagation. When the altitude of the target is low, the peak intensity of relay propagation is much larger than that of direct propagation. However, because of the limitation of the relay system aperture for relay propagation and the variation of coherence length for direct propagation, the difference in peak intensity between the two propagations decreases with the increase of the target altitude.     

Differential confocal measurement method of linear scanning based on dual linear array camera北大核心CSCD

针对目前微观三维表面形貌测量技术中存在检测效率和测量范围较小的问题,提出一种基于双线阵相机的线扫描差动共聚焦三维形貌测量方法。采用线扫描光源,利用线扫描拼接算法,分别合成焦前和焦后图像;再利用差动算法获得样本位于测量区域的差动图像,结合预先刻度的轴向响应曲线,完成样本的三维形貌还原,实现大范围高效测量。实验结果证明:基于双线阵相机的线扫描差动共聚焦三维形貌测量方法在相同时间内测量范围和测量效率分别是白光干涉仪的16.48倍和6.59倍,并且该方法在测量过程中不需要停顿,只需实现一次对焦,就可以对样品进行连续不间断的扫描检测。研究成果为满足智能制造中在线在位、实时高效、大范围测量的检测需求提供依据。     

勘误北大核心CSCD

《强激光与粒子束》2019年31卷第2期020101论文:高功率半导体激光器倍频实现紫外光输出胡列懋,李志永,刘松阳,宁方晋,谭荣清(1.中国科学院电子学研究所高功率气体激光技术部,北京100190;2.中国科学院大学电子电气与通信工程学院,北京100049)     

更正北大核心CSCD

阵列设计作为多输入多输出(MIMO)雷达成像系统中的一项关键技术直接影响系统成像性能。通过分析MIMO雷达成像模型,探讨了基于等效阵列概念的MIMO阵列设计方法,并讨论了近场效应对成像结果的影响。基于所构建的MIMO雷达成像实验系统,进行了近场微小金属目标二维成像试验。实验结果表明:该阵列设计方法在120~150 GHz的适用性,验证了毫米波MIMO雷达近场成像能力。     

Upgrade of beam energy measurement system at BEPC-Ⅱ

The beam energy measurement system is of great importance for both BEPC-Ⅱ accelerator and BES-III detector. The system is based on measuring the energies of Compton back-scattered photons. In order to meet the requirements of data taking and improve the measurement accuracy, the system has continued to be upgraded, which involves the updating of laser and optics subsystems, replacement of a view-port of the laser to the vacuum insertion subsystem, the use of an electric cooling system for a high purity germanium detector, and improvement of the data acquisition and processing subsystem. The upgrade system guarantees the smooth and efficient measurement of beam energy at BEPC-II and enables accurate offline energy values for further physics analysis at BES-Ⅲ.     

Finite element beam propagation method for analysis of plasmonic waveguide

The basic idea of the finite element beam propagation method (FE-BPM) is described.It is applied to calculate the fundamental mode of a channel plasmonic polariton (CPP) waveguide to confirm its validity. Both the field distribution and the effective index of the fundamental mode are given by the method.The convergence speed shows the advantage and stability of this method.Then a plasmonic waveguide with a dielectric strip deposited on a metal substrate is investigated,and the group velocity is negative for the fundamental mode of this kind of waveguide.The numerical result shows that the power flow direction is reverse to that of phase velocity.     

Multi-path propagation of acoustical wave and time reversal field in a solid plate

The multi-path effect of the acoustical wave in a solid plate is studied. The multireflection and wave conversion of the cylindrical compressional and shear waves, which are excited by an infinite strip on a free surface of the solid plate, are analyzed thoroughly by the far-field approximation method. The concise analytical representations of the cylindrical waves are obtained. The time reversal processing is then applied to the propagation of the cylindrical waves and analyzed theoretically and experimentally. It is shown that the waves coming from different array elements and different paths all arrive at the original place after the time reversal operation. It indicates that the time reversal can compensate automatically the wave aberration caused by the multi-path effect. The self-adaptive focusing of the time reversal field is also analyzed quantificationally by the focusing gain and the ratio of the principal to the second lobe. The effects of the focus position and the aperture of the transducer array on the focused field are also investigated. It shows that theoretical and experimental results are consistent to each other very well.     

The determination of the parameters of “spherical” motion in a kerr field

The problem of the existence of class M geodesic motions on the surface r=const, all of whose mechanical parameters in the specified Kerr field are determined only from stability conditions, is posed and investigated. A system of equations which determines this class is derived and solved. It is shown that in the general case this motion does not cover the entire surface r=const and is restricted by the condition ₀ }- ₀. Simple algebraic expressions are found for all the parameters of these configurations-energy, momentum, radius, and the angle ₀-as functions of the specific angular momentuma of the Kerr field. It is shown that these motions can exist only in Kerr fields with a value of the parametera larger or equal to r_g/2. In a Kerr field with a fixed value ofa there exist only two configurations with the indicated properties. In conclusion, the properties of the M-solutions associated with the appearance of configurations with negative energies and negativeness of g₀₀ within the limits of some configurations and values ofa larger than r_g/2 are discussed. It is noted that the negative values of the energy occur only in those configurations within whose limits g₀₀ < 0. It is also pointed out that the Kerr field is free of pathological properties associated with the breakdown of causality whena > r_g/2 if one does not made the assumption, unnecessary within the framework of the problem under discussion, that the sources of the Kerr field are in the region r=0.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 17–25, May, 1979.The authors express their gratitude to A. A. Grib for useful discussions.     

Selection of near infrared spectral information based on section combination moving window partial least squares北大核心CSCD

Selection of near infrared spectral information is research focus on the application of NIR, which enable to simplify the model and improve accuracy of prediction. Aiming at selecting optimal modeling spectral width of near infrared spectroscopy, section combination moving window partial least squares (SCMWPLS) is proposed in this paper. This method selects continuous modeling screened interval.by continuously varying size of moving window and cross validation. Taking Glucose solution near-infrared spectroscopy as test specimen, near infrared prediction models are established respectively by proposed method, and traditional interval partial least squares (IPLS) and moving window partial least squares (MWPLS). Comparing proposed method with two traditional methods, squares prediction RMSE is decreased by 44% and 25% respectively. © 2017, Editorial Board, Journal of Applied Optics. All right reserved.     

Ultrasound Attenuation in s-wave Two-band Superconductors北大核心CSCD

s~±-波电子配对被认为很可能用于解释铁基超导体的配对机制.本文中,我们计算了s~±-波二带超导体的超声衰减系数,并利用T-矩阵近似研究了杂质的影响.我们的计算表明,当两带的能隙大小相当时,超声衰减-温度曲线中出现一个Hebel-Slichter峰.我们同时验证了核自旋弛豫率的研究中发现的低温下的共振束缚态效应.