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双波长拍波干涉测长中拍波干涉条纹尾数的测量方法 总被引:2,自引:0,他引:2
描述在拍波干涉测长中使用的几种拍波干涉条纹尾数测量方法,提出一种拍波锁相型对准原理,介绍和比较拍波干涉仪的三个原理方案,讨论测量方法和测量精度等问题. 相似文献
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自然界中的昆虫和鸟类大都采用拍翼飞行的策略,其优越的气动表现使拍动飞行方式备受关注.值得注意的是,拍动飞行昆虫和鸟类在实现高机动性的同时,产生的噪音并不十分显著.因此,对拍翼飞行的流固声耦合问题进行研究,揭示其飞行动力学和声学特性,对于应用这类飞行技术具有重要的指导意义.文章采用一种浸入边界法对拍翼悬停时的流固声耦合问题进行数值模拟研究.具体针对刚性拍翼和不同刚度、质量比的柔性拍翼进行了数值模拟,分析了拍翼刚度和质量比对拍翼悬停时的升力和声学特性的影响.结果表明拍翼的转动能有效增加升力,提高效率并降低拍翼运动产生的声音;同时悬停拍翼的近场声受涡的影响明显,尤其是在较大的转动角度时;引入适当的弹性可有效提高拍翼在悬停时的气动表现,包括提高升力系数和效率;综合考虑气动和声学表现,可以看出当无量纲拍动频率在0.3~0.4时,低质量的拍翼(拍翼-流体质量比为1.0)产生的声音较小,同时又具备较高的效率. 相似文献
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将传统的"拍"现象演示装置与现代的计算机多媒体教学技术结合,用麦克风采集拍音信号,并通过音箱放大,同时将采集到的信号输入到计算机中,利用频谱分析软件进行实时分析,并将拍信号投影在大屏幕上,使学生全面、直观地认识、掌握拍的概念. 相似文献
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The beat spectrum between modes of a gas laser having a resonator with a plane-and-sphere mirror system was studied. Intense beats were detected in the 0–1.5 Mc range. It is shown that the presence of low-frequency beats can be associated with the nonideality of the resonator. The intensity of the beats was found to depend on their spectral composition and on the degree of beam limiting. This effect is related to the presence of antiphase oscillation zones in the laser beam for azimuthal modes and to the variation of the interference pattern with time when the beam is limited in the focus of the objective. 相似文献
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Fifth-order phase-sensitive detection of ultrafast polarization beats in cascade four-level system 下载免费PDF全文
We study the colour-locked twin-noisy-field correlation effects in the fifth-order nonlinear susceptibility of ultrafast polarization beats in a cascade four-level system. More importantly, the fifth-order phase-sensitive heterodyne detection of ultrafast polarization beats has been exploited. The fifth-order nonlinear optical response can be controlled and modified through the colour-locked correlation of twin noisy fields. Thus, this method with the phase dispersion information is a good way to measure the real and imaginary parts of the fifth-order nonlinear susceptibility. 相似文献
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For Λ-type three-level atomic systems we have clarified using diagram that (1) it is impossible to observe quantum beats due to the ground state sublevels by measuring the time dependence of the fluorescence intensity, and (2) why it is physically possible to observe and how we can observe quantum beats in the ground state sublevels by using fluorescence. Generalization of the results shows that we can determine from which state (the ground state or the excited state) the quantum beats are originated. Analytical result is shown for four-level atomic systems. 相似文献
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Interaction between forward bulk magnetostatic waves propagating in a structure consisting of two planar films separated by a nonmagnetic spacer is studied. When two modes are excited in the structure, a phase mismatch between them produces symmetric, asymmetric, and “forked” beats of the amplitudes of the magnetically coupled modes. It is shown that the parameters of the beats can be controlled by varying the magnetic field intensity and ration between the initial amplitudes of the modes excited in the structure. 相似文献
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Gilbert J. Perlow 《Hyperfine Interactions》1992,72(1-3):49-62
A discussion is given of the time-behavior of recoil-free γ-radiation passing through a resonant medium. The classical dispersion
theory of Hamermesh is extended to account for different linewidths in source or absorber so that a synchrotron-radiation
source can be simulated. A result, essentially the same as that of Kagan et al., follows in the limit of large source width.
A review is given of the quantum beats which result from the absorption of one line of a frequency-modulation spectrum. An
example is given of the measurement of second-order Doppler shift in Fe−Be by the method of quantum beats. Finally, there
is a discussion of the measurement by quantum beats of the very small energy shift in a57Co−Cu source by a magnetic field. 相似文献
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We report experimental studies of absorption quantum beats induced by electron spin coherence in GaAs quantum wells. Absorption quantum beats occur for strongly localized excitons, but nearly vanish for mobile excitons in the third order nonlinear optical response. Pronounced quantum beats for mobile excitons emerge in an unusual fifth order process. These results, along with a qualitative analysis based on the use of N-exciton eigenstates, elucidate how the manifestation of electron spin coherence in the excitonic nonlinear optical response can differ fundamentally from that in an atomic system. 相似文献
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O. Aoud P. Disseix J. Leymarie A. Vasson E. Aujol B. Beaumont 《Superlattices and Microstructures》2004,36(4-6):607
It is shown that excitonic transients of bulk GaN can be accurately measured by an interferometric correlation technique used in reflection geometry. This is demonstrated for resonantly excited excitons in high quality GaN epilayers. The interferograms exhibit a clear modulation of the signal due the quantum beats between A and B excitons. The period of these beats is in good agreement with the A–B exciton energy splitting measured by means of frequency-resolved reflectivity. The decrease of the overall signal is mainly connected to the crystal quality and strongly dependent on the inhomogeneous broadening which can be extracted from the correlation spectra. These results are in agreement with numerical calculations based on the Fourier transform determination of the time-resolved reflection coefficient in the framework of linear semi-classical theory carried out in order to obtain the autocorrelation response. 相似文献
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It is shown that coherence between nondegenerate sublevels of an atomic ground state is efficiently induced by means of a short resonant light pulse. The free precession of the coherence causes beats in forward stattering of a probe beam, which can sensitively be detected by a polarization technique. Zeeman beats on the 4f6 6s27 F1-4f6 6s6p 7F0 transition of samarium were observed. In sodium vapor transient ground state coherence was detected in a single-shot measurement. 相似文献