共查询到20条相似文献,搜索用时 187 毫秒
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利用声波引起的光衍射现象检测叉指换能器激发的声场分布的简单光探针技术,对YZ-LiNbO_3晶体表面几种不同参量的等指长线性调频叉指换能器向两端辐射声功率流的不对称分配进行了实验研究。并利用Smith等效电路模型,考虑叉指电极引起表面阻抗不连续而产生的指间多次反射效应,对上述问题进行了数值计算。实验测量和理论计算的结果基本上符合,并由此得出了几点简单的结论。同时也提出了值得进一步深入研究和改进的问题。 相似文献
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叉指换能器不仅是高效率的表面波换能器,而且往往也是有效的体波换能器。对表面波器件来说,这些体波将带来杂散影响,需加以抑制。与此相反,“表面掠射体波”(以下简称SSBW)器件,不是利用叉指激发的表面波,而正是利用它激发的体波来完成信号处理功能的。 这种体波由叉指换能器激发,形成紧沿表面传播的波束,其传播矢量几乎完全平行压电晶体表面,并满足表面边界条件。它的传播速度V_s与衰减基本上同于无限大介质中相同方向的体波。其同步频率满足下列关系 相似文献
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在研究摩擦力驱动的接触式转动马达的基础上,本文研制了一种由声表面波驱动的非接触式转动马达.这种马达的定子选用128°YX-LiNbO3晶体,在晶体表面光刻两对叉指换能器,由叉指换能器在定子表面激发两列平行而反向传播的声表面波.定子表面铺一层流体,转子就浮在流体表面.当定子表面有两列平行而反向的声表面波传播时,流体层中就会产生平行而反向的声流,这种黏性流体的声流运动就会驱动转子运动.实验上测定了马达的角速度随驱动电压,流体层厚度以及流体运动黏性系数变化的结果.同时,我们也发现,在相同工作频率下,非接触式转动马达的阈值电压远小于接触式. 相似文献
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偶氮苯液晶薄膜相位共轭的光学记录研究 总被引:1,自引:0,他引:1
利用间并四波混频研究了一种偶氮苯液昌聚合物的相位共轭和光学记录特性,在近共振条件下,用低功率Nd:YAG倍频激光得到高效率的相位共轭光和高阶衍射光,当光强达到10W/cm^2量级时,薄膜显示出光记录效应,即在撒掉写入光之后,相位共轭波并不消失,进一步大光强到10^3W/cm^2量级时,出现三组分别只与前向泵浦光,后向泵浦光和信号有关的高阶衍射光。其中观察到第三阶衍射光,且在撒掉任两束光后,所剩一束 相似文献
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We investigate the diffraction properties of multiple-superimposed index gratings from a vector synthetic viewpoint using coupled wave analysis with Bragg and non-Bragg readout. The vector synthetic gratings consist of two volume-index gratings with different grating wave vectors, which can be obtained in photorefractive materials, in optical fibers or in Bragg cells with two driving acoustic waves. This structure can realize beam splitting, beam combining, and beam cross coupling, etc. Analytic expressions for the diffraction efficiency as well as the amplitude of the waves involved are obtained. The results are presented and discussed. 相似文献
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Polarization anomalies of the Brewster type are considered for processes such as wave reflection, wave scattering, wave diffraction by surface grating and surface plasmon waves. Generalized conditions for Brewster anomalies in wave diffraction are written in analytical form. The application of the Brewster phenomenon for integrated optical polarizers is investigated numerically. 相似文献
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LOU Ci-bo TANG Li-qin SONG Dao-hong WANG Xiao-sheng XU Jing-jun CHEN Zhi-gang 《Frontiers of Physics》2008,3(1):1
The study of wave propagation in periodic systems is at the frontiers of physics, from fluids to condensed matter physics, and from photonic crystals to Bose-Einstein condensates. In optics, a typical example of periodic system is a closely-spaced waveguide array, in which collective behavior of wave propagation exhibits many intriguing phenomena that have no counterpart in homogeneous media. Even in a linear waveguide array, the diffraction property of a light beam changes due to evanescent coupling between nearby waveguide sites, leading to normal and anomalous discrete diffraction. In a nonlinear waveguide array, a balance between diffraction and self-action gives rise to novel localized states such as spatial “discrete solitons” in the semi-infinite (or total-internal-reflection) gap or spatial “gap solitons” in the Bragg reflection gaps. Recently, in a series of experiments, we have “fabricated” closely-spaced waveguide arrays (photonic lattices) by optical induction. Such photonic structures have attracted great interest due to their novel physics, link to photonic crystals, as well as potential applications in optical switching and navigation. In this review article, we present a brief overview on our experimental demonstrations of a number of novel spatial soliton phenomena in light-induced photonic bandgap structures, including self-trapping of fundamental discrete solitons and more sophisticated lattice gap solitons. Much of our work has direct impact on the study of similar discrete phenomena in systems beyond optics, including sound waves, water waves, and matter waves (Bose-Einstein condensates) propagating in periodic potentials. 相似文献
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光盘光学系统的矢量衍射理论分析 总被引:5,自引:3,他引:2
本文以完整的矢量衍射理论分析了光盘光学系统。首先将入射的聚焦光束分解为平面波谱 ,得到每个平面波的振幅矢量 ;然后计算光盘对每个平面波的衍射 ,得到衍射波的振幅矢量 ,从而得到了整个衍射波场的空间频谱 ;最后计算物镜光瞳上的能通量 ,得到光盘系统的读出信号。在衍射计算中 ,光盘被定义为二维金属光栅 ,根据信息符的不同模型 ,选用坐标变换方法、耦合波方法或模态方法。对于典型的 DVD光学系统来说 ,矢量理论的结论与标量理论相差甚远 ,要得到正确的结果就必须采用矢量衍射理论 相似文献
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Ci-bo LOU Li-qin TANG Dao-hong SONG Xiao-sheng WANG Jing-jun XU Zhi-gang CHEN 《Frontiers of Physics in China》2008,3(1):1-12
The study of wave propagation in periodic systems is at the frontiers of physics, from fluids to condensed matter physics,
and from photonic crystals to Bose-Einstein condensates. In optics, a typical example of periodic system is a closely-spaced
waveguide array, in which collective behavior of wave propagation exhibits many intriguing phenomena that have no counterpart
in homogeneous media. Even in a linear waveguide array, the diffraction property of a light beam changes due to evanescent
coupling between nearby waveguide sites, leading to normal and anomalous discrete diffraction. In a nonlinear waveguide array,
a balance between diffraction and self-action gives rise to novel localized states such as spatial “discrete solitons” in
the semi-infinite (or total-internal-reflection) gap or spatial “gap solitons” in the Bragg reflection gaps. Recently, in
a series of experiments, we have “fabricated” closely-spaced waveguide arrays (photonic lattices) by optical induction. Such
photonic structures have attracted great interest due to their novel physics, link to photonic crystals, as well as potential
applications in optical switching and navigation. In this review article, we present a brief overview on our experimental
demonstrations of a number of novel spatial soliton phenomena in light-induced photonic bandgap structures, including self-trapping
of fundamental discrete solitons and more sophisticated lattice gap solitons. Much of our work has direct impact on the study
of similar discrete phenomena in systems beyond optics, including sound waves, water waves, and matter waves (Bose-Einstein
condensates) propagating in periodic potentials.
相似文献
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Wave-particle duality is one of the most fundamental and mysterious natures of matters.Here,we present an interesting scheme of isolated electron wave packet diffraction with a few-cycle laser pulse and an extreme ultraviolet (XUV) pulse.The diffraction fringes are clearly present in the laser dressed XUV photoelectron spectra,strongly resembling the Airy diffraction pattern of optical waves.This phenomenon suggests a great potential of attosecond diffractometry.According to this scheme we also propose a simple method to determine the XUV pulse duration from the photoelectron spectra with a rather high resolution. 相似文献
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Recently various models for spatially chaotic structures have been proposed. We study the diffraction patterns produced by plane chaotic waves incident on one-dimensional chaotic point scatterers. The spacing between the scatterers and the dynamics of the incident wave are given by a logistic map or standard map. We find a sharp diffraction peak when the incident dynamics is produced by the same map as the structure of the spatial configuration. The diffraction pattern is symmetric about the incident direction only if the map dynamics is invertible. Diffraction patterns with chaotic incident waves have a large signal-to-noise ratio and are well suited for pattern identification. We discuss possible applications to the scattering of microwaves from aperiodic structures. (c) 1997 American Institute of Physics. 相似文献
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采用了Hansen矢量波函数理论研究半圆形金属光栅的衍射效率问题,该方法适用于任意入射方向,任意偏振态入射场衍射问题的研究,结果表明,当入射光为p或s型偏振光时,其结果与文献(1)的结果相同。 相似文献
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Noniterative phase retrieval from a single diffraction intensity pattern by use of an aperture array
Nakajima N 《Physical review letters》2007,98(22):223901
A noniterative method for retrieving the phase of a wave field from a diffraction intensity measurement in a coherent wave field is proposed. In this method, the phase can be calculated from analytic equations based on the properties of entire functions by use of Fourier transforms. This method requires only a single measurement of the intensity of a diffracted wave through an array filter of rectangular apertures and then does not need to use any lens systems and coherent reference waves. Therefore, it provides a potentially useful means for coherent imaging in a wide class of wave fields such as optical, x ray, electron, and atomic waves. 相似文献