高频沟槽叉指体声波换能器

本文介绍了一种由压电晶体沟槽表面上的叉指换能器构成的新型体声波换能器。制作在X切LiNbO_3,表面的横波换能器在213MHz时的一次换能损耗为3.8dB.     

线性调频叉指换能器辐射声功率流的不对称分配

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。     

用脉冲重叠法精确测定表面声波的传播速度

本文提出采用交叉触发脉冲重叠法来精确测定材料的表面声波相速度.在一块样品上制作相同的三个叉指换能器A、B、C,在B与C之间的样品表面镀上金属膜.分别依次由A或C发射表面声波,而由其它两个换能器接收,即可测定表面声波的速度和速度变化.本文对LiNbO,石英及压电陶瓷样品进行了测量,测量精度估计约为±2m/s.     

表面掠射体波(SSBW)

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     

叉指换能器激发表面声波的生长特性

本文利用暗场法和光探针技术对叉指换能器,特别是线性调频叉指换能器,激发表面声波的生长特性进行了观察和测量。并且利用有关的理论进行了计算。实验和理论结果一致表明在共振激发指对的中心位置,声强极小;离开中心位置,声强迅速增长。对于周期性叉指换能器,向两侧增长是对称的;而对于线性调频叉指换能器,向两侧增长是不对称的,向高频端的增长比向低频端的更强,因而形成线性调频叉指换能器向两端辐射的不对称性。但是在实验结果与理论结果的比较中,也出现一些问题,我们对此进行了初步的讨论。     

压电晶体-液体-固体声波导中叉指换能器对导波的激发研究

本文对压电晶体－液体－各向同性固体结构的声波导中叉指换能器所激发的导波进行了理论研究和数值分析,给出了导波的相速度、叉指换能器激发导波的机电耦合系数与液体层归一化厚度、晶体取向之间的关系曲线,同时,还探讨了声波导中的位移场和电势场分布。     

声表面波驱动的非接触式转动马达

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.     

物理学报第27卷1978年总目录

第l期光衍射法观测叉指换能器在石英晶体中激发的各种声波…………………………张淑仪 高学奎f 1)小注入下晶体管,c—yee特性的指数因子的研究…………………………………陈星弼易明觥(10)钕玻璃的光泵感应热畸变……………中国科学院上海光学精密机械研究所钕玻璃热畸变研究组(22)群表示论的物理方法(III)…………………………………………………陈金全王凡高美娟(31)晶体电光和非线性光学效应的离子基团理论(IV)……………………………………………陈创天(41)三维晶格统计模型的一种封闭的近似解…………………………………石赫许以超郝…     

声表面波在压电晶体表面上的聚焦特性

研究了压电晶体表面上圆弧形叉指换能器产生的声表面波的聚焦现象。用作者提出的压电晶体表面激发的严格矢量场理论来计算会聚的表面波声场,取代了比较流行的源于光学的标量角谱理论。理论分析表明介质的各向异性对声束的会聚特性有很大的影响,如焦长和焦点附近声场的对称性。在实验中可以用光学暗场法来观察声表面波场的会聚。尽管各向异性介质或各向异性压电晶体上表面波声场的会聚都非常复杂,实验的结果和理论分析比较一致。     

Implementation of GHz SAW filters using quasi-harmonic interdigital transducers

本文利用准谐频设计方法,在常规光刻工艺水平上,成功地实现了GHz级声表面波(SAW)器件。准谐频叉指换能器(QHIDT)的优点为其指条宽与指间隙可以比一般的单指换能器宽,克服了单指换能器内指间的多次反射,并且又较好地解决了普通谐频叉指换能器基频抑制不好的缺点。本文给出了制作在ST石英基片上,工作频率1128MHz的声表面波滤波器的实验结果。     

偶氮苯液晶薄膜相位共轭的光学记录研究

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     

Beam splitting, combining, and cross coupling through multiple superimposed volume-index gratings

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.     

Generalization of the Brewster phenomenon for the wave diffraction process

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.     

Novel spatial solitons in light-induced photonic bandgap structures

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.      

光盘光学系统的矢量衍射理论分析

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     

Isolated attosecond electron wave packet diffraction

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.     

Sharp diffraction peaks from chaotic structures

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.     

Method of Coupled Waves in the Theory of Diffraction of Light by Elastic Waves in Crystals

Diffraction of light by elastic waves in crystals is described by the method of coupled waves in a form different from that used by other researchers. The difference is determined by the treatment of two pairs of orthogonal coordinate systems whose principal axes are oriented along the directions of phase and energy transfer of two optical waves interacting on a sound wave. Due to this, the equations of coupled waves assume the most compact form, which was previously unknown for crystals. These equations are easily solved by the conventional methods in terms of quasi-plane waves and also admit of a wider class of solutions for bounded interaction regions. Two different diffraction regimes are compared in the present work, namely, the transmission and reflection diffraction. It is indicated that the suggested approach allows one to refine the parameters that define the efficiency of diffraction of light by elastic waves in crystals.     

半圆形金属光栅的矢量模态理论

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。     

散射光彩色数字全息光学系统及波面重建算法研究

令物体表面为散射面,参考光及重建光为球面波,详细研究了离轴数字全息物光场重建平面的光波场.导出物光、共轭物光及零级衍射光分布与光学系统参数的关系.根据彩色数字全息的特点,提出抑制零级衍射干扰的光学系统设计方法,并且对一种能够避免插值误差的波面重建算法进行了优化研究,给出了相应的实验证明.